OPTICAL SYSTEM

Abstract

The invention relates to an optical system (7) having an optical axis (OA), having a display unit (5) for displaying an image, having an eyepiece (6) for viewing the image, the eyepiece (6) comprising a lens unit (L1). The display unit (5) is designed in such away that a marginal ray light beam (9) emanates from an edge (8) of the display unit (5) and propagates to the lens unit (L1) in a light incidence direction (L). The display unit (5) is arranged first along the optical axis (OA) in the light incidence direction (L), followed by the lens unit (L1) arranged on the optical axis (OA). No further optical unit of the optical system (7) is arranged between the lens unit (L1) and a pupil of the eye (2). The marginal ray light beam (9) has a chief ray (HS). The chief ray (HS) propagates at a first chief ray height (H1) at the lens unit (L1) and at a second chief ray height (H2) at the display unit (5). The first chief ray height (H1) is at least level with the second chief ray height (H2).

Claims

1. An optical system (7), having: an optical axis (OA); a display unit (5) for displaying an image, the display unit (5) being arranged on the optical axis (OA) and having an edge (8), the edge (8) delimiting the display unit (5); an eyepiece (6) for viewing the image, the eyepiece (6) comprising a lens unit (L1); wherein the edge (8) of the display unit (5) is designed in such a way that a marginal ray light beam (9) emanates from the edge (8) of the display unit (5) and propagates to the lens unit (L1) in a light incidence direction (L), the marginal ray light beam (9) having a chief ray (HS); the display unit (5) is arranged first along the optical axis (OA) in the light incidence direction (L), followed by the lens unit (L1) arranged on the optical axis (OA); no further optical unit of the optical system (7) is arranged between the lens unit (L1) and a pupil of the eye (2); the optical system (7) is designed in such a way that the chief ray (HS) propagates at a first chief ray height (H1) at the lens unit (L1), the first chief ray height (H1) being a first distance between the optical axis (OA) and the chief ray (HS) at the lens unit (L1); the display unit (5) is designed in such a way that the chief ray (HS) propagates at a second chief ray height (H2) at the display unit (5), the second chief ray height (H2) being a second distance between the optical axis (OA) and the chief ray (HS) at the display unit (5), characterized by one of the following features: (i) the first chief ray height (H1) is at least level with the second chief ray height (H2); (ii) the first chief ray height (H1) has a greater value than the second chief ray height (H2).

2. The optical system (7) as claimed in claim 1, characterized in that at least one of the following features is present: (i) the first distance is the length of a first straight line which is aligned perpendicular to the optical axis (OA) and connects a first point (P1) on the optical axis (OA) to a second point (P2) on the chief ray (HS) at the lens unit (L1); (ii) the second distance is the length of a second straight line which is aligned perpendicular to the optical axis (OA) and connects a third point (P3) on the optical axis (OA) to a fourth point (P4) on the chief ray (HS) at the display unit (5).

3. The optical system (7) as claimed in claim 2, characterized in that at least one of the following features is present: (i) the lens unit (L1) has a first surface (surface 2) and a second surface (surface 3), the first surface (surface 2) of the lens unit (L1) being arranged on a first side of the lens unit (L1) facing away from the display unit (5), the second surface (surface 3) of the lens unit (L1) being arranged on a second side of the lens unit (L1) facing the display unit (5), a first plane being arranged on the first surface (surface 2) of the lens unit (L1), and the first straight line being located in the first plane; (ii) the display unit (5) has a surface (surface 10, surface 13, surface 15, surface 17, surface 24), the surface (surface 10, surface 13, surface 15, surface 17, surface 24) of the display unit (5) being arranged on a side of the display unit (5) facing the lens unit (L1), a second plane being arranged on the surface (surface 10, surface 13, surface 15, surface 17, surface 24) of the display unit (5), and the second straight line being located in the second plane.

4. The optical system (7) as claimed in claim 1, characterized in that the optical system (7) comprises at least two identical lenses (L1, L4) which have an aspheric form.

5. The optical system (7) as claimed in claim 1, characterized in that the optical system (7) comprises a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4), a fifth lens (L5), and a sixth lens (L6), with the first lens (L1) being arranged first along the optical axis (OA) as seen counter to the light incidence direction (L), followed by the second lens (L2), then the third lens (L3), then the fourth lens (L4), then the fifth lens (L5), and then the sixth lens (L6), the first lens (L1) having positive refractive power, the second lens (L2) having negative refractive power, the third lens (L3) having positive refractive power, the fourth lens (L4) having positive refractive power, the fifth lens (L5) having positive refractive power, and the sixth lens (L6) having negative refractive power.

6. The optical system (7) as claimed in claim 5, characterized in that the optical system (7) has at least one of the following features: (i) the optical system (7) comprises at least one cemented member (L1, L2); (ii) the first lens (L1) has a surface (surface 2) directed at the pupil of the eye, the surface (surface 2) having an aspheric form; (iii) the sixth lens (L6) has a surface (surface 12) directed at the display unit (5), the surface (surface 12) having an aspheric form.

7. The optical system (7) as claimed in claim 1, characterized in that the optical system (7) has at least one intermediate image (ZB).

8. The optical system (7) as claimed in claim 7, characterized in that the optical system (7) has one of the following features: (i) a first concave lens surface (surface 5) and a second concave lens surface (surface 6), the intermediate image (ZB) being arranged between the first concave lens surface (surface 5) and the second concave lens surface (surface 6); (ii) a first meniscus-shaped lens (L2) with a first concave lens surface (surface 5) and a second meniscus-shaped lens (L3) with a second concave lens surface (surface 6), the intermediate image (ZB) being arranged between the first concave lens surface (surface 5) and the second concave lens surface (surface 6); (iii) a first meniscus-shaped cemented member (L8, L9) with a first concave lens surface (surface 16) and a second meniscus-shaped cemented member (L11, L12) with a second concave lens surface (surface 22), a pupil being arranged between the first concave lens surface (surface 16) and the second concave lens surface (surface 22).

9. The optical system (7) as claimed in claim 7, characterized in that exactly one lens (L1) is arranged between the pupil of the eye (2) and the intermediate image (ZB).

10. The optical system (7) as claimed in claim 9, characterized in that the exactly one lens (L1) has a bi-aspheric form.

11. The optical system (7) as claimed in claim 7, characterized in that the optical system (7) has the following features: (i) the eyepiece (6) comprises a first lens group (LG1) and a second lens group (LG2, LG2′); (ii) as seen counter to the light incidence direction (L), the first lens group (LG1) is arranged first along the optical axis (OA), followed by the second lens group (LG2, LG2′); (iii) the intermediate image (ZB) is arranged between the first lens group (LG1) and the second lens group (LG2, LG2′).

12. The optical system (7) as claimed in claim 11, characterized in that the optical system (7) comprises a third lens group (LG3′), and in that as seen counter to the light incidence direction (L), the first lens group (LG1) is arranged first along the optical axis (OA), followed by the second lens group (LG2′) and then the third lens group (LG3′).

13. The optical system (7) as claimed in claim 11, characterized in that the first lens group (LG1) comprises the lens unit (L1).

14. The optical system (7) as claimed in claim 11, characterized in that the optical system (7) has the following features: (i) the first lens group (LG1) comprises a first lens (L1), a second lens (L2), a third lens (L3), and a fourth lens (L4), with, as seen counter to the light incidence direction (L), the first lens (L1) being arranged first along the optical axis (OA), followed by the second lens (L2), then the third lens (L3), and then the fourth lens (L4), the first lens (L1) having positive refractive power, the second lens (L2) having positive refractive power, the third lens (L3) having positive refractive power, and the fourth lens (L4) having negative refractive power; (ii) the second lens group (LG2) comprises a fifth lens (L5), a sixth lens (L6), a seventh lens (L7), an eighth lens (L8), a ninth lens (L9), a tenth lens (L10), an eleventh lens (L11), and a twelfth lens (L12), with, as seen counter to the light incidence direction (L), the fifth lens (L5) being arranged first along the optical axis (OA), followed by the sixth lens (L6), then the seventh lens (L7), then the eighth lens (L8), then the ninth lens (L9), then the tenth lens (L10), then the eleventh lens (L11), and then the twelfth lens (L12), the fifth lens (L5) having positive refractive power, the sixth lens (L6) having positive refractive power, the seventh lens (L7) having negative refractive power, the eighth lens (L8) having negative refractive power, the ninth lens (L9) having positive refractive power, the tenth lens (L10) having positive refractive power, the eleventh lens (L11) having positive refractive power, and the twelfth lens (L12) having negative refractive power.

15. The optical system (7) as claimed in claim 14, characterized in that the optical system (7) has at least one of the following features: (i) the second lens group (LG2) comprises at least one meniscus-shaped cemented member (L8, L9, L11, L12); (ii) the second lens group (LG2) comprises at least one meniscus-shaped cemented member (L8, L9, L11, L12) comprising a crown lens and a flint lens; (iii) the second lens group (LG2) comprises at least one meniscus-shaped cemented member (L8, L9, L11, L12) having a concave side (surface 16, surface 21), the concave side (surface 16, surface 21) being directed at a pupil arranged in the optical system (7); (iv) the eighth lens (L8) of the second lens group (LG2) and the ninth lens (L9) of the second lens group (LG2) form a first meniscus-shaped cemented member; (v) the eleventh lens (L11) of the second lens group (LG2) and the twelfth lens (L12) of the second lens group (LG2) form a second meniscus-shaped cemented member; (vi) the seventh lens (L7) of the second lens group (LG2) is in the form of a meniscus lens.

16. The optical system (7) as claimed in claim 11, characterized in that the optical system (7) has the following features: (i) the first lens group (LG1) comprises a first lens (L1) and a second lens (L2), with, as seen counter to the light incidence direction (L), the first lens (L1) being arranged first along the optical axis (OA), followed by the second lens (L2), the first lens (L1) having positive refractive power and the second lens (L2) having negative refractive power; (ii) the second lens group (LG2) comprises a third lens (L3), a fourth lens (L4), a fifth lens (L5), a sixth lens (L6), and a seventh lens (L7), with, as seen counter to the light incidence direction (L), the third lens (L3) being arranged first along the optical axis (OA), followed by the fourth lens (L4), then the fifth lens (L5), then the sixth lens (L6), and then the seventh lens (L7), the third lens (L3) having negative refractive power, the fourth lens (L4) having positive refractive power, the fifth lens (L5) having negative refractive power, the sixth lens (L6) having positive refractive power, and the seventh lens (L7) having positive refractive power.

17. The optical system (7) as claimed in claim 16, characterized in that the optical system (7) has at least one of the following features: (i) the first lens (L1) has a bi-aspheric form; (ii) the second lens (L2) is in the form of a meniscus lens; (iii) the third lens (L3) is in the form of a meniscus lens; (iv) the fourth lens (L4) has a bi-aspheric form; (v) the fifth lens (L5) and the sixth lens (L6) form a cemented member.

18. The optical system (7) as claimed in claim 11, characterized in that the optical system (7) has the following features: (i) the first lens group (LG1) comprises a first lens (L1) and a second lens (L2), with, as seen counter to the light incidence direction (L), the first lens (L1) being arranged first along the optical axis (OA), followed by the second lens (L2), the first lens (L1) having a bi-aspheric form and the second lens (L2) being in the form of a meniscus lens; (ii) the second lens group (LG2) comprises a third lens (L3), a fourth lens (L4), a fifth lens (L5), a sixth lens (L6), a seventh lens (L7), and an eighth lens (L8), with, as seen counter to the light incidence direction (L), the third lens (L3) being arranged first along the optical axis (OA), followed by the fourth lens (L4), then the fifth lens (L5), then the sixth lens (L6), then the seventh lens (L7), and then the eighth lens (L8), the third lens (L3) being in the form of a meniscus lens, the fourth lens (L4) having a bi-aspheric form, and the seventh lens (L7) and the eighth lens (L8) forming a cemented member.

19. The optical system (7) as claimed in claim 18, characterized in that the optical system (7) has one of the following features: (i) the first lens (L1) has positive refractive power and the second lens (L2) has negative refractive power; (ii) the first lens (L1) has positive refractive power and the second lens (L2) has positive refractive power; (iii) the third lens (L3) has positive refractive power, the fourth lens (L4) has positive refractive power, the fifth lens (L5) has negative refractive power, the sixth lens (L6) has positive refractive power, the seventh lens (L7) has negative refractive power, and the eighth lens (L8) has positive refractive power; (iv) the third lens (L3) has positive refractive power, the fourth lens (L4) has positive refractive power, the fifth lens (L5) has negative refractive power, the sixth lens (L6) has positive refractive power, the seventh lens (L7) has positive refractive power, and the eighth lens (L8) has negative refractive power.

20. The optical system (7) as claimed in claim 11, characterized in that the optical system (7) has the following features: (i) the first lens group (LG1) comprises a single lens in the form of a first lens (L1), the first lens (L1) having positive refractive power; (ii) the second lens group (LG2) comprises a second lens (L2), a third lens (L3), a fourth lens (L4), a fifth lens (L5), and a sixth lens (L6), with, as seen counter to the light incidence direction (L), the second lens (L2) being arranged first along the optical axis (OA), followed by the third lens (L3), then the fourth lens (L4), then the fifth lens (L5), and then the sixth lens (L6), the second lens (L2) having positive refractive power, the third lens (L3) having negative refractive power, the fourth lens (L4) having positive refractive power, the fifth lens (L5) having positive refractive power, and the sixth lens (L6) having negative refractive power.

21. The optical system (7) as claimed in claim 20, characterized in that the optical system (7) has at least one of the following features: (i) the first lens (L1) has a bi-aspheric form; (ii) the second lens (L2) has a bi-aspheric form; (iii) the third lens (L3) is in the form of a meniscus lens; (iv) the fifth lens (L5) and the sixth lens (L6) form a cemented member.

22. The optical system (7) as claimed in claim 11, characterized in that the optical system (7) has the following features: (i) the first lens group (LG1) comprises a single lens in the form of a first lens (L1), the first lens (L1) having positive refractive power; (ii) the second lens group (LG2) comprises a second lens (L2), a third lens (L3), and a fourth lens (L4), with, as seen counter to the light incidence direction (L), the second lens (L2) being arranged first along the optical axis (OA), followed by the third lens (L3), and then the fourth lens (L4), the second lens (L2) having positive refractive power, the third lens (L3) having positive refractive power, and the fourth lens (L4) having negative refractive power.

23. The optical system (7) as claimed in claim 22, characterized in that the optical system (7) has at least one of the following features: (i) the first lens (L1) has a bi-aspheric form; (ii) the second lens (L2) has a bi-aspheric form; (iii) the third lens (L3) has a bi-aspheric form.

24. The optical system (7) as claimed in claim 11, characterized in that the optical system (7) has the following features: (i) the first lens group (LG1) comprises a single lens in the form of a first lens (L1), the first lens (L1) having positive refractive power; (ii) the second lens group (LG2) comprises a second lens (L2), a third lens (L3), a fourth lens (L4), a fifth lens (L5), and a sixth lens (L6), with, as seen counter to the light incidence direction (L), the second lens (L2) being arranged first along the optical axis (OA), followed by the third lens (L3), then the fourth lens (L4), then the fifth lens (L5), and then the sixth lens (L6), the second lens (L2) having positive refractive power, the third lens (L3) having negative refractive power, the fourth lens (L4) having negative refractive power, the fifth lens (L5) having positive refractive power, and the sixth lens (L6) having positive refractive power.

25. The optical system (7) as claimed in claim 24, characterized in that the optical system (7) has at least one of the following features: (i) the first lens (L1) has a bi-aspheric form; (ii) the second lens (L2) has a bi-aspheric form; (iii) the sixth lens (L6) has an aspheric form; (iv) the fourth lens (L4) and the fifth lens (L5) form a cemented member.

26. The optical system (7) as claimed in claim 11, characterized in that the optical system (7) has the following features: (i) the first lens group (LG1) comprises a single lens in the form of a first lens (L1), the first lens (L1) having positive refractive power; (ii) the second lens group (LG2) comprises a second lens (L2), a third lens (L3), a fourth lens (L4), a fifth lens (L5), a sixth lens (L6), and a seventh lens (L7), with, as seen counter to the light incidence direction (L), the second lens (L2) being arranged first along the optical axis (OA), followed by the third lens (L3), then the fourth lens (L4), then the fifth lens (L5), then the sixth lens (L6), and then the seventh lens (L7), the second lens (L2) having positive refractive power, the third lens (L3) having negative refractive power, the fourth lens (L4) having negative refractive power, the fifth lens (L5) having positive refractive power, the sixth lens (L6) having positive refractive power, and the seventh lens (L7) having positive refractive power.

27. The optical system (7) as claimed in claim 26, characterized in that the optical system (7) has at least one of the following features: (i) the first lens (L1) has a bi-aspheric form; (ii) the second lens (L2) has a bi-aspheric form; (iii) the fourth lens (L4) and the fifth lens (L5) form a cemented member.

28. The optical system (7) as claimed in claim 1, characterized in that the optical system (7) is in the form of a dioptric system.

29. The optical system (7) as claimed in claim 1, characterized in that the optical system (7) has one of the following features: (i) a distance from the pupil of the eye (2) to the lens unit (L1) is greater than one focal length of the optical system (7); (ii) a distance from the pupil of the eye (2) to the lens unit (L1) is at least 1.25 times greater than one focal length of the optical system (7); (iii) a distance from the pupil of the eye (2) to the lens unit (L1) is at least 1.5 times greater than one focal length of the optical system (7); (iv) a distance from the pupil of the eye (2) to the lens unit (L1) is 1.7 times greater than one focal length of the optical system (7).

Description

[0071] Further practical embodiments and advantages of the invention are described below in conjunction with the drawings, in which:

[0072] FIG. 1 shows a schematic representation of a piece of night vision equipment having an optical system according to the invention;

[0073] FIG. 2 shows a schematic representation of a first embodiment of an optical system according to the invention;

[0074] FIG. 3 shows system data of the optical system in accordance with FIG. 2;

[0075] FIG. 4 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system in accordance with FIGS. 2 and 3;

[0076] FIG. 5 shows a schematic representation of a second embodiment of an optical system according to the invention;

[0077] FIG. 6 shows system data of the optical system in accordance with FIG. 5;

[0078] FIG. 7 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system in accordance with FIGS. 5 and 6;

[0079] FIG. 8 shows a schematic representation of a third embodiment of an optical system according to the invention;

[0080] FIG. 9 shows system data of the optical system in accordance with FIG. 8;

[0081] FIG. 10 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system in accordance with FIGS. 8 and 9;

[0082] FIG. 11 shows a schematic representation of a fourth embodiment of an optical system according to the invention;

[0083] FIG. 12 shows system data of the optical system in accordance with FIG. 11;

[0084] FIG. 13 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system in accordance with FIGS. 11 and 12;

[0085] FIG. 14 shows a schematic representation of a fifth embodiment of an optical system according to the invention;

[0086] FIG. 15 shows system data of the optical system in accordance with FIG. 14;

[0087] FIG. 16 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system in accordance with FIGS. 14 and 15;

[0088] FIG. 17 shows a schematic representation of a sixth embodiment of an optical system according to the invention;

[0089] FIG. 18 shows system data of the optical system in accordance with FIG. 17;

[0090] FIG. 19 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system in accordance with FIGS. 17 and 18;

[0091] FIG. 20 shows a schematic representation of a seventh embodiment of an optical system according to the invention;

[0092] FIG. 21 shows system data of the optical system in accordance with FIG. 20;

[0093] FIG. 22 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system in accordance with FIGS. 20 and 21;

[0094] FIG. 23 shows a schematic representation of an eighth embodiment of an optical system according to the invention;

[0095] FIG. 24 shows system data of the optical system in accordance with FIG. 23;

[0096] FIG. 25 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system in accordance with FIGS. 23 and 24;

[0097] FIG. 26 shows a schematic representation of a ninth embodiment of an optical system according to the invention;

[0098] FIG. 27 shows system data of the optical system in accordance with FIG. 26;

[0099] FIG. 28 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system in accordance with FIGS. 26 and 27;

[0100] FIG. 29 shows a schematic representation of an embodiment of a further optical system according to the invention;

[0101] FIG. 30 shows a schematic representation of an aperture aberration, of image surface positions, and of the relative distortion for an optical system according to FIG. 29 with a maximum spatial region;

[0102] FIG. 31 shows a schematic representation of an aperture aberration, of image surface positions, and of the relative distortion for an optical system according to FIG. 29 with a centered pupil of the eye with a diameter of 3 mm;

[0103] FIG. 32 shows a schematic representation of the transverse aberrations for a centered pupil of the eye with a diameter of 3 mm in the case of an optical system according to FIG. 29;

[0104] FIG. 33 shows a schematic representation of the transverse aberrations for a pupil of the eye with a diameter of 3 mm, laterally off-centered relative to the optical axis by 1 mm, in the case of an optical system according to FIG. 29;

[0105] FIG. 34 shows a schematic representation of the transverse aberrations for a pupil of the eye with a diameter of 3 mm, laterally off-centered relative to the optical axis by 2 mm, in the case of an optical system according to FIG. 29;

[0106] FIG. 35 shows curves of a modulation transfer function in the case of an optical system according to FIG. 29 with a centered pupil of the eye with a diameter of 3 mm;

[0107] FIG. 36 shows curves of a modulation transfer function in the case of an optical system according to FIG. 29 with a pupil of the eye with a diameter of 3 mm, laterally off-centered relative to the optical axis by 1 mm;

[0108] FIG. 37 shows curves of a modulation transfer function in the case of an optical system according to FIG. 29 with a pupil of the eye with a diameter of 3 mm, laterally off-centered relative to the optical axis by 2 mm;

[0109] FIG. 38 shows system data of the optical system in accordance with FIG. 29; and

[0110] FIG. 39 shows a sphere coefficients for surfaces of the optical system in accordance with FIG. 29.

[0111] The optical system according to the invention will now be explained in more detail using a piece of night vision equipment. Explicit reference is made to the fact that the invention is not restricted to the use in night vision equipment. Instead, the invention can be used for any optical equipment for which the invention is suitable. By way of example, the optical system according to the invention is arranged in a pair of field glasses, in a refractor, in a telescope, in a spotting scope, or in a light microscope.

[0112] FIG. 1 shows a schematic representation of a piece of night vision equipment 1, by means of which a user of the piece of night vision equipment 1 can observe an object O by placing an eye 2 against the piece of night vision equipment 1. The piece of night vision equipment 1 comprises an objective 3 and a detector 4. The detector 4 detects light rays which pass from the object O through the objective 3 and generates detection signals. These detection signals are electronically converted in such a way that they are presented as an image on a display unit 5. Further, the piece of night vision equipment 1 comprises an eyepiece 6, by means of which the user of the piece of night vision equipment 1 can observe the image presented on the display unit 5.

[0113] By way of example, the detector 4 can be in the form of a CCD detector or CMOS detector. However, the invention is not restricted to the aforementioned embodiment. Rather, the detector 4 can be any detector suitable for the invention.

[0114] By way of example, a field emission visual display unit, a liquid crystal visual display unit, a thin film transistor visual display unit, a plasma visual display unit, an SED (surface conduction electron emitter display), or a visual display unit containing organic light-emitting diodes can be used as a display unit 5. The above enumeration is not exhaustive. Rather, any display unit suitable for the invention can be used as display unit 5.

[0115] As depicted in FIG. 1, the light rays originating from the object O enter the piece of night vision equipment 1 in a light incidence direction L. Therefore, the light rays initially pass through the objective 3 and are subsequently detected by the detector 4.

[0116] By way of example, the arrangement of the abovementioned units of the piece of night vision equipment 1 along an optical axis OA of the piece of night vision equipment 1 can be described as follows: As seen counter to the light incidence direction L, that is to say as seen from the eye 2 in the direction of the object O, the eyepiece 6 is arranged first along the optical axis OA of the piece of night vision equipment 1, followed by the display unit 5, then the detector 4, and then the objective 3.

[0117] An optical system according to the invention is depicted using dashed lines in FIG. 1 and provided with reference sign 7. The optical system 7 according to the invention comprises the eyepiece 6 and the display unit 5.

[0118] Embodiments of the optical system 7 according to the invention are explained in more detail below.

[0119] FIG. 2 shows a first embodiment of the optical system 7 according to the invention, which has an optical axis OA that corresponds to the optical axis OA of the piece of night vision equipment 1. The eyepiece 6 of the optical system 7 according to the invention comprises a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6.

[0120] As seen counter to the light incidence direction L, the first lens L1 is arranged first along the optical axis OA, followed by the second lens L2, then the third lens L3, then the fourth lens L4, then the fifth lens L5, and then the sixth lens L6. The first lens L1 has positive refractive power. The second lens L2 has negative refractive power. The third lens L3 has positive refractive power. The fourth lens L4 has positive refractive power. The fifth lens L5 has positive refractive power and the sixth lens L6 has negative refractive power. The first lens L1 and the second lens L2 form a cemented member.

[0121] The first lens L1 forms the aforementioned lens unit of the optical system 7 according to the invention. As seen in the light incidence direction L, the display unit 5 is arranged first along the optical axis OA, followed by the first lens L1 along the optical axis OA. No further optical unit of the optical system 7 is arranged between the first lens L1 and an eye pupil of the eye 2.

[0122] A marginal ray light beam 9 emanates from an edge 8 of the display unit 5 and propagates to the first lens L1 in the light incidence direction L. The marginal ray light beam 9 has a multiplicity of light rays which form the marginal ray light beam 9. One of the light rays is a chief ray HS of the marginal ray light beam 9. The chief ray HS is a ray of the marginal ray light beam 9 which represents the marginal ray light beam 9 when an aperture of the optical system 7 is reduced to almost 0. The chief ray HS propagates at a first chief ray height H1 at the first lens L1, the first chief ray height H1 being a first distance between the optical axis OA and the chief ray HS at the first lens L1. For example, the first distance is the length of a first straight line which is aligned perpendicular to the optical axis OA and connects a first point P1 on the optical axis OA to a second point P2 on the chief ray HS at the first lens L1. In particular, the first distance can also be given as follows: As will be explained further below, the first lens L1 has a first surface and a second surface. The first surface is arranged on a first side of the first lens L1 facing away from the display unit 5. Further, the second surface is arranged on a second side of the first lens L1 facing the display unit 5. A first plane is arranged on the first surface of the first lens L1, the first straight line being located in the first plane. By way of example, the first plane is in contact with the first surface at at least one point. The chief ray HS propagates at a second chief ray height H2 at the display unit 5, the second chief ray height H2 being a second distance between the optical axis OA and the chief ray HS at the display unit 5. For example, the second distance is the length of a second straight line which is aligned perpendicular to the optical axis OA and connects a third point P3 on the optical axis OA to a fourth point P4 on the chief ray HS at the display unit 5. In particular, the second distance can also be given as follows: As will be explained further below, the display unit 5 has a surface. The surface of the display unit 5 is arranged on a side of the display unit 5 facing the first lens L1. Further, a second plane is arranged on the surface of the display unit 5. The second straight line is located in the second plane. By way of example, the second plane is in contact with the surface of the display unit 5 at at least one point.

[0123] The first chief ray height H1 has a greater value than the second chief ray height H2. By way of example, the first chief ray height H1 is approximately 12 mm and the second chief ray height H2 is approximately 10 mm. The invention is not restricted to the aforementioned magnitudes of the first chief ray height H1 and the second chief ray height H2. Rather, any first chief ray height H1 and any second chief ray height H2 which are suitable for the invention can be used for the invention.

[0124] The system data of the embodiment of the optical system 7 according to the invention in accordance with FIG. 2 emerge from the upper table in FIG. 3. The upper table in FIG. 3 is based on an incoming beam radius of 2.5 mm, an entrance angle of 27°, and an effective focal length of the optical system 7 according to the invention of 10.814 mm. The surface 0 denotes a surface at an infinite distance in front of the optical system 7 on the side of the eye 2 so that light can enter the optical system 7 in collimated fashion. The surface 1 denotes the surface of the eye pupil of the eye 2. The first lens L1 has a surface 2 directed at the eye 2. The second lens L2 has a surface 3 directed at the eye 2 and a surface 4 directed at the display unit 5. The third lens L3 has a surface 5 directed at the eye 2 and a surface 6 directed at the display unit 5. The fourth lens L4 has a surface 7 directed at the eye 2 and a surface 8 directed at the display unit 5. The fifth lens L5 has a surface 9 directed at the eye 2 and a surface 10 directed at the display unit 5. Further, the sixth lens L6 has a surface 11 directed at the eye 2 and a surface 12 directed at the display unit 5. The surface 13 denotes the surface of the display unit 5. Further, the upper table in FIG. 3 specifies the radii of the individual surfaces and the thicknesses of the individual lenses of the optical system 7 according to the invention in accordance with FIG. 2, with the thickness of a lens being defined as the distance between a first vertex at the optical axis OA of a surface of the lens directed at the eye 2 and a second vertex at the optical axis OA of a surface of the lens directed at the display unit 5. A thickness between two of the aforementioned lenses denotes the distance between two vertices of two adjacent surfaces of two lenses.

[0125] The upper table in FIG. 3 specifies the material of the individual lenses, the material specification corresponding to the nomenclature as used by the company OHARA. Moreover, the refractive indices are given for three different wavelengths of the light rays originating from the object O, specifically a wavelength 1 of 587.6 nm, a wavelength 2 of 435.8 nm, and a wavelength 3 of 643.8 nm. Further, the half diameters of the individual lenses and the refractive powers of the individual lenses are specified in the upper table in FIG. 3.

[0126] The first lens L1 has the surface 2 directed at the eye pupil of the eye 2. The surface 2 has an aspheric form. Further, the sixth lens L6 has the surface 12 directed at the display unit 5. The surface 12 has an aspheric form. The aspheric form of the two aforementioned surfaces is determined by the asphere formula, which is given by

[00001]$\begin{array}{cc}z\left(h\right)=\frac{h^2}{R.Math.\left(1+\sqrt{1-\left(1+k\right).Math.\frac{h^2}{R^2}}\right)}+{.Math.}_{i=2}^M{C}_{i-1}{h}^{2i}& \left[1\right]\end{array}$

where [0127] (i) z is the surface sagitta value, [0128] (ii) h is the height of incidence of a light ray on the aspheric surface of the lens, [0129] (iii) k is the conic constant, [0130] (iv) R is the vertex radius of the surface, and [0131] (v) C.sub.i are asphere coefficients

[0132] The asphere coefficients and the conic constant are specified in the lower table in FIG. 3.

[0133] FIG. 4 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system 7 according to the invention in accordance with FIGS. 2 and 3. Shown are a sagittal contrast curve S (shown in solid lines) and a tangential contrast curve T (shown in dashed lines) for 20 line pairs per millimeter, 40 line pairs per millimeter, and 60 line pairs per millimeter.

[0134] The embodiment of the optical system 7 according to the invention in accordance with FIGS. 2 to 4 allows the first chief ray height H1 to be able to be for example 9 mm in the case of a pupil distance of for example 18 mm between the eye pupil of the eye 2 and the first lens L1. If use is made of a display unit 5 whose display height is less than 9 mm, this may necessitate large negative refractive power immediately when the light from the display unit 5 enters the eyepiece 6. Such a negative refractive power leads to a divergence of the chief ray away from the optical axis OA. However, the negative refractive power initially has practically no effect on the marginal ray light beam 9. In order to ensure the convergence of the chief ray HS to the pupil of the eye, a strong positive refractive power must be introduced into the optical system 7 downstream. This strong positive refractive power, for instance in the form of the third lens L3, the fourth lens L4, and the fifth lens L5, leads to a strong shortening of the optical system 7, since the strong positive refractive power now has a strong effect on the marginal ray light beam 9 and thus very quickly collimates the light emanating from the display unit 5. As a result, the optical system 7 is shortened. Finally, on account of this short installation length, it is difficult to introduce correction units, for example in the form of lenses, into the optical system 7. The embodiments of the optical system 7 according to the invention explained below have a longer installation length than the embodiment of the optical system 7 according to the invention described in FIGS. 2 to 4, and so this disadvantage can be avoided.

[0135] FIG. 5 shows a second embodiment of the optical system 7 according to the invention, which has an optical axis OA that corresponds to the optical axis OA of the piece of night vision equipment 1. An eyepiece 6 comprises a first lens group LG1 and a second lens group LG2. As seen counter to the light incidence direction L, the first lens group LG1 is arranged first along the optical axis OA, followed by the second lens group LG2. An intermediate image ZB is arranged between the first lens group LG1 and the second lens group LG2.

[0136] The first lens group LG1 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 5 comprises a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4. As seen counter to the light incidence direction L, the first lens L1 is arranged first along the optical axis OA, followed by the second lens L2, then the third lens L3, and then the fourth lens L4, the first lens L1 having positive refractive power, the second lens L2 having positive refractive power, the third lens L3 having positive refractive power, and the fourth lens L4 having negative refractive power.

[0137] The second lens group LG2 of the embodiment of the optical system 7 according to the invention in FIG. 5 comprises a fifth lens L5, a sixth lens L6, a seventh lens L7, an eighth lens L8, a ninth lens L9, a tenth lens L10, an eleventh lens L11, and a twelfth lens L12. As seen counter to the light incidence direction L, the fifth lens L5 is arranged first along the optical axis OA, followed by the sixth lens L6, then the seventh lens L7, then the eighth lens L8, then the ninth lens L9, then the tenth lens L10, then the eleventh lens L11, and then the twelfth lens L12, the fifth lens L5 having positive refractive power, the sixth lens L6 having positive refractive power, the seventh lens L7 having negative refractive power, the eighth lens L8 having negative refractive power, the ninth lens L9 having positive refractive power, the tenth lens L10 having positive refractive power, the eleventh lens L11 having positive refractive power, and the twelfth lens L12 having negative refractive power.

[0138] The seventh lens L7 is meniscus shaped. Further, the eighth lens L8 and the ninth lens L9 form a first meniscus-shaped cemented member. Moreover, the eleventh lens L11 and the twelfth lens L12 form a second meniscus-shaped cemented member. At least one of the aforementioned cemented members may have a concave side. The concave side is directed at a pupil arranged in the optical system 7 according to the invention. The pupil arranged in the optical system 7 according to the invention is arranged on the optical axis OA where a chief ray HS of a marginal ray light beam 9 intersects the optical axis OA.

[0139] In the embodiment of the optical system 7 according to the invention of FIG. 5, too, the first lens L1 forms the aforementioned lens unit of the optical system 7 according to the invention. As seen in the light incidence direction L, the display unit 5 is arranged first along the optical axis OA, followed by the first lens L1 along the optical axis OA. No further optical unit of the optical system 7 is arranged between the first lens L1 and an eye pupil of the eye 2.

[0140] The marginal ray light beam 9 emanates from an edge 8 of the display unit 5 and propagates to the first lens L1 in the light incidence direction L. The marginal ray light beam 9 has a multiplicity of light rays which form the marginal ray light beam 9. One of the light rays is the chief ray HS of the marginal ray light beam 9. The chief ray HS propagates at a first chief ray height H1 at the first lens L1, the first chief ray height H1 being a first distance between the optical axis OA and the chief ray HS at the first lens L1. For example, the first distance is the length of a first straight line which is aligned perpendicular to the optical axis OA and connects a first point P1 on the optical axis OA to a second point P2 on the chief ray HS at the first lens L1. In particular, the first distance can also be given as follows: As will be explained further below, the first lens L1 has a first surface and a second surface. The first surface is arranged on a first side of the first lens L1 facing away from the display unit 5. Further, the second surface is arranged on a second side of the first lens L1 facing the display unit 5. A first plane is arranged on the first surface of the first lens L1, the first straight line being located in the first plane. By way of example, the first plane is in contact with the first surface at at least one point. The chief ray HS propagates at a second chief ray height H2 at the display unit 5, the second chief ray height H2 being a second distance between the optical axis OA and the chief ray HS at the display unit 5. For example, the second distance is the length of a second straight line which is aligned perpendicular to the optical axis OA and connects a third point P3 on the optical axis OA to a fourth point P4 on the chief ray HS at the display unit 5. In particular, the second distance can also be given as follows: As will be explained further below, the display unit 5 has a surface. The surface of the display unit 5 is arranged on a side of the display unit 5 facing the first lens L1. Further, a second plane is arranged on the surface of the display unit 5. The second straight line is located in the second plane. By way of example, the second plane is in contact with the surface of the display unit 5 at at least one point.

[0141] The first chief ray height H1 has a greater value than the second chief ray height H2. By way of example, the first chief ray height H1 is approximately 10 mm and the second chief ray height H2 is approximately 5.3 mm. The invention is not restricted to the aforementioned magnitudes of the first chief ray height H1 and the second chief ray height H2. Rather, any first chief ray height H1 and any second chief ray height H2 which are suitable for the invention can be used for the invention.

[0142] The system data of the embodiment of the optical system 7 according to the invention in accordance with FIG. 5 emerge from the table in FIG. 6. The table in FIG. 6 is based on an incoming beam radius of 2.5 mm, an entrance angle of 27°, and an effective focal length of the optical system 7 according to the invention of −10.914 mm. The surface 0 denotes a surface at an infinite distance in front of the optical system 7 on the side of the eye 2 so that light can enter the optical system 7 in collimated fashion. Further, the surface 1 denotes the surface of the eye pupil of the eye 2. The first lens L1 has a surface 2 directed at the eye 2 and a surface 3 directed at the display unit 5. The second lens L2 has a surface 4 directed at the eye 2 and a surface 5 directed at the display unit 5. The third lens L3 has a surface 6 directed at the eye 2 and a surface 7 directed at the display unit 5. The fourth lens L4 has a surface 8 directed at the eye 2 and a surface 9 directed at the display unit 5. The fifth lens L5 has a surface 10 directed at the eye 2 and a surface 11 directed at the display unit 5. Further, the sixth lens L6 has a surface 12 directed at the eye 2 and a surface 13 directed at the display unit 5. The seventh lens L7 has a surface 14 directed at the eye 2 and a surface 15 directed at the display unit 5. The eighth lens L8 has a surface 16 directed at the eye 2. The ninth lens L9 has a surface 17 directed at the eye 2 and a surface 18 directed at the display unit 5. The tenth lens L10 has a surface 19 directed at the eye 2 and a surface 20 directed at the display unit 5. The eleventh lens L11 has a surface 21 directed at the eye 2. Further, the twelfth lens L12 has a surface 22 directed at the eye 2 and a surface 23 directed at the display unit 5. The surface 24 denotes the surface of the display unit 5. Further, the table in FIG. 6 specifies the radii of the individual surfaces and the thicknesses of the individual lenses of the optical system 7 according to the invention in accordance with FIG. 5, with the thickness of a lens being defined as the distance between a first vertex at the optical axis OA of a surface of the lens directed at the eye 2 and a second vertex at the optical axis OA of a surface of the lens directed at the display unit 5. A thickness between two of the aforementioned lenses denotes the distance between two vertices of two adjacent surfaces of two lenses.

[0143] The table in FIG. 6 specifies the material of the individual lenses, the material specification corresponding to the nomenclature as used by the company OHARA. Moreover, the refractive indices are given for three different wavelengths of the light rays originating from the object O, specifically a wavelength 1 of 587.6 nm, a wavelength 2 of 435.8 nm, and a wavelength 3 of 643.8 nm. Further, the half diameters of the individual lenses and the refractive powers of the individual lenses are specified in the table in FIG. 6.

[0144] FIG. 7 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system 7 according to the invention in accordance with FIGS. 5 and 6. Shown are a sagittal contrast curve S (shown in solid lines) and a tangential contrast curve T (shown in dashed lines) for 20 line pairs per millimeter, 40 line pairs per millimeter, and 60 line pairs per millimeter.

[0145] The embodiment of the optical system 7 according to the invention in accordance with FIGS. 5 to 7 is a purely spherical embodiment. In principle, this embodiment is a combination of an optical unit in the form of the first lens group LG1 with a relay system in the form of the second lens group LG2, with the relay system imaging the image of the object O displayed on the display unit 5 onto the intermediate image ZB. The pupil plane is arranged between the seventh lens L7 and the eighth lens L8 and is conjugate paraxially to the pupil of the eye. The fourth lens L4, the eighth lens L8, and the twelfth lens L12, each having negative refractive power, are made of a flint glass, for example. All further lenses of this embodiment of the optical system 7 according to the invention are formed from a crown glass, for example. In this embodiment of the optical system 7 according to the invention, the Petzval sum is corrected, for example, by the fourth lens L4 with negative refractive power and by the seventh lens L7 embodied as a meniscus lens, by the meniscus-shaped cemented member consisting of the eighth lens L8 and the ninth lens L9, and by the meniscus-shaped cemented member consisting of the eleventh lens L11 and the twelfth lens L12. In order to minimize the overall refractive power of the aforementioned individual lenses, the image plane on the display unit 5 deviates significantly from telecentricity. There is therefore a negative exit pupil position, that is to say the exit pupil is located within the optical system 7 according to the invention with a strongly divergent chief ray HS at the display unit 5. The significant deviation from telecentricity therefore also substantially distinguishes this embodiment of the optical system 7 according to the invention from an eyepiece that is used on a refractor or a pair of field glasses of the prior art.

[0146] FIG. 8 shows a third embodiment of the optical system 7 according to the invention, which has an optical axis OA that corresponds to the optical axis OA of the piece of night vision equipment 1. An eyepiece 6 comprises a first lens group LG1 and a second lens group LG2. As seen counter to the light incidence direction L, the first lens group LG1 is arranged first along the optical axis OA, followed by the second lens group LG2. An intermediate image ZB is arranged between the first lens group LG1 and the second lens group LG2. More precisely, the intermediate image ZB is arranged on a surface of a lens of the first lens group LG1, as will be explained further below.

[0147] The first lens group LG1 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 8 comprises a first lens L1 and a second lens L2. As seen counter to the light incidence direction L, the first lens L1 is arranged first along the optical axis OA, followed by the second lens L2. The first lens L1 has positive refractive power. The second lens L2 has negative refractive power.

[0148] The second lens group LG2 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 8 comprises a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. As seen counter to the light incidence direction L, the third lens L3 is arranged first along the optical axis OA, followed by the fourth lens L4, then the fifth lens L5, then the sixth lens L6, and then the seventh lens L7. The third lens L3 has negative refractive power. The fourth lens L4 has positive refractive power. The fifth lens L5 has negative refractive power. The sixth lens L6 has positive refractive power and the seventh lens L7 has positive refractive power.

[0149] The first lens L1 has a bi-aspheric form. Further, the second lens L2 and the third lens L3 each are in the form of a meniscus lens. Moreover, the fourth lens L4 has a bi-aspheric form. The fifth lens L5 and the sixth lens L6 form a cemented member.

[0150] In the embodiment of the optical system 7 according to the invention in accordance with FIG. 8, too, the first lens L1 forms the aforementioned lens unit of the optical system 7 according to the invention. As seen in the light incidence direction L, the display unit 5 is arranged first along the optical axis OA, followed by the first lens L1 along the optical axis OA. No further optical unit of the optical system 7 is arranged between the first lens L1 and an eye pupil of the eye 2.

[0151] A marginal ray light beam 9 emanates from an edge 8 of the display unit 5 and propagates to the first lens L1 in the light incidence direction L. The marginal ray light beam 9 has a multiplicity of light rays which form the marginal ray light beam 9. One of the light rays is a chief ray HS of the marginal ray light beam 9. The chief ray HS propagates at a first chief ray height H1 at the first lens L1, the first chief ray height H1 being a first distance between the optical axis OA and the chief ray HS at the first lens L1. For example, the first distance is the length of a first straight line which is aligned perpendicular to the optical axis OA and connects a first point P1 on the optical axis OA to a second point P2 on the chief ray HS at the first lens L1. In particular, the first distance can also be given as follows: As will be explained further below, the first lens L1 has a first surface and a second surface. The first surface is arranged on a first side of the first lens L1 facing away from the display unit 5. Further, the second surface is arranged on a second side of the first lens L1 facing the display unit 5. A first plane is arranged on the first surface of the first lens L1, the first straight line being located in the first plane. By way of example, the first plane is in contact with the first surface at at least one point. The chief ray HS propagates at a second chief ray height H2 at the display unit 5, the second chief ray height H2 being a second distance between the optical axis OA and the chief ray HS at the display unit 5. For example, the second distance is the length of a second straight line which is aligned perpendicular to the optical axis OA and connects a third point P3 on the optical axis OA to a fourth point P4 on the chief ray HS at the display unit 5. In particular, the second distance can also be given as follows: As will be explained further below, the display unit 5 has a surface. The surface of the display unit 5 is arranged on a side of the display unit 5 facing the first lens L1. Further, a second plane is arranged on the surface of the display unit 5. The second straight line is located in the second plane. By way of example, the second plane is in contact with the surface of the display unit 5 at at least one point.

[0152] The first chief ray height H1 has a greater value than the second chief ray height H2. By way of example, the first chief ray height H1 is approximately 10.9 mm and the second chief ray height H2 is approximately 5.3 mm. The invention is not restricted to the aforementioned magnitudes of the first chief ray height H1 and the second chief ray height H2. Rather, any first chief ray height H1 and any second chief ray height H2 which are suitable for the invention can be used for the invention.

[0153] The system data of the embodiment of the optical system 7 according to the invention in accordance with FIG. 8 emerge from the upper table in FIG. 9. The upper table in FIG. 9 is based on an incoming beam radius of 2.5 mm, an entrance angle of 27°, and an effective focal length of the optical system 7 according to the invention of −10.842 mm. The surface 0 denotes a surface at an infinite distance in front of the optical system 7 on the side of the eye 2 so that light can enter the optical system 7 in collimated fashion. Further, the surface 1 denotes the surface of the eye pupil of the eye 2. The first lens L1 has a surface 2 directed at the eye 2 and a surface 3 directed at the display unit 5. The second lens L2 has a surface 4 directed at the eye 2 and a surface 5 directed at the display unit 5. The third lens L3 has a surface 6 directed at the eye 2 and a surface 7 directed at the display unit 5. The fourth lens L4 has a surface 8 directed at the eye 2 and a surface 9 directed at the display unit 5. The fifth lens L5 has a surface 10 directed at the eye 2. Further, the sixth lens L6 has a surface 11 directed at the eye 2 and a surface 12 directed at the display unit 5. The seventh lens L7 has a surface 13 directed at the eye 2 and a surface 14 directed at the display unit 5. The surface 15 denotes the surface of the display unit 5. Further, the upper table in FIG. 9 specifies the radii of the individual surfaces and the thicknesses of the individual lenses of the optical system 7 according to the invention in accordance with FIG. 8, with the thickness of a lens being defined as the distance between a first vertex at the optical axis OA of a surface of the lens directed at the eye 2 and a second vertex at the optical axis OA of a surface of the lens directed at the display unit 5. A thickness between two of the aforementioned lenses denotes the distance between two vertices of two adjacent surfaces of two lenses.

[0154] The intermediate image ZB is arranged on the surface 5 of the second lens L2.

[0155] The upper table in FIG. 9 specifies the material of the individual lenses, the material specification corresponding to the nomenclature as used by the company OHARA. Moreover, the refractive indices are given for three different wavelengths of the light rays originating from the object O, specifically a wavelength 1 of 587.6 nm, a wavelength 2 of 435.8 nm, and a wavelength 3 of 643.8 nm. Further, the half diameters of the individual lenses and the refractive powers of the individual lenses are specified in the upper table in FIG. 9.

[0156] The surfaces 2 and 3 of the first lens L1 have an aspheric form. Further, the surfaces 8 and 9 of the fourth lens L4 have an aspheric form. The aspheric form of the aforementioned surfaces is given by the asphere formula [1] mentioned above. The asphere coefficients and the conic constant are specified in the lower table in FIG. 9.

[0157] FIG. 10 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system 7 according to the invention in accordance with FIGS. 8 and 9. Shown are a sagittal contrast curve S (shown in solid lines) and a tangential contrast curve T (shown in dashed lines) for 20 line pairs per millimeter, 40 line pairs per millimeter, and 60 line pairs per millimeter.

[0158] The embodiment of the optical system 7 according to the invention in accordance with FIGS. 8 to 10 has a reduced number of lenses—specifically seven lenses—in comparison with the embodiment of the optical system 7 according to the invention explained further above. In this embodiment of the optical system 7 according to the invention, too, the intermediate image ZB is arranged between the first lens group LG1 and the second lens group LG2. Once again, the intermediate image ZB is generated by the second lens group LG2, which is essentially designed as a relay system. As mentioned above, the second lens L2 and the third lens L3 are in the form of a meniscus lens. The second lens L2 and the third lens L3 are arranged so that the intermediate image ZB is arranged between the second lens L2 and the third lens L3, with no further optical unit of the optical system 7 according to the invention being arranged between firstly the second lens L2 and the intermediate image ZB and secondly the third lens L3 and the intermediate image ZB. The second lens L2 in the form of a meniscus lens and the third lens L3 in the form of a meniscus lens serve to correct the Petzval sum, and thus contribute to flattening of the image field.

[0159] The first lens L1 and the fourth lens L4 have a bi-aspheric form. This makes it possible to implement a beam deflection using lenses with a high refractive power. In the process, arising aberrations, in particular spherical aberrations, are corrected on account of the aspheric form of the first lens L1 and the fourth lens L4. It is consequently possible to use a smaller number of lenses in the optical system 7 according to the invention in comparison with the embodiment of the optical system 7 according to the invention explained further above. This applies in particular to the first lens group LG1, which in this embodiment of the optical system 7 according to the invention comprises only two lenses, specifically the first lens L1 and the second lens L2, on account of the bi-aspheric form of the first lens L1 and the fourth lens L4. In addition, it is advantageous that a longitudinal chromatic aberration can be corrected by the cemented member, which is formed by the fifth lens L5 and the sixth lens L6. The aforementioned cemented member is an achromatic cemented member, for example. In particular, provision is made for the fifth lens L5 to be made of a flint glass and for the sixth lens L6 to be made of a crown glass. The further lenses of this embodiment of the optical system 7 according to the invention are formed from a crown glass, for example.

[0160] FIG. 11 shows a fourth embodiment of the optical system 7 according to the invention, which has an optical axis OA that corresponds to the optical axis OA of the piece of night vision equipment 1. An eyepiece 6 comprises a first lens group LG1 and a second lens group LG2. As seen counter to the light incidence direction L, the first lens group LG1 is arranged first along the optical axis OA, followed by the second lens group LG2. An intermediate image ZB is arranged between the first lens group LG1 and the second lens group LG2. More precisely, the intermediate image ZB is arranged on a surface of a lens of the first lens group LG1, as will be explained further below.

[0161] The first lens group LG1 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 11 comprises a first lens L1 and a second lens L2. As seen counter to the light incidence direction L, the first lens L1 is arranged first along the optical axis OA, followed by the second lens L2. The first lens L1 has positive refractive power. The second lens L2 has negative refractive power.

[0162] The second lens group LG2 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 11 comprises a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8. As seen counter to the light incidence direction L, the third lens L3 is arranged first along the optical axis OA, followed by the fourth lens L4, then the fifth lens L5, then the sixth lens L6, then the seventh lens L7, and then the eighth lens L8. The third lens L3 has positive refractive power. The fourth lens L4 has positive refractive power. The fifth lens L5 has negative refractive power. The sixth lens L6 has positive refractive power. The seventh lens L7 has negative refractive power and the eighth lens L8 has positive refractive power.

[0163] The first lens L1 has a bi-aspheric form. The second lens L2 and the third lens L3 are in the form of a meniscus lens. The fourth lens L4 has a bi-aspheric form. Further, the seventh lens L7 and the eighth lens L8 form a cemented member.

[0164] In the embodiment of the optical system 7 according to the invention in accordance with FIG. 11, too, the first lens L1 forms the aforementioned lens unit of the optical system 7 according to the invention. As seen in the light incidence direction L, the display unit 5 is arranged first along the optical axis OA, followed by the first lens L1 along the optical axis OA. No further optical unit of the optical system 7 according to the invention is arranged between the first lens L1 and an eye pupil of the eye 2.

[0165] A marginal ray light beam 9 emanates from an edge 8 of the display unit 5 and propagates to the first lens L1 in the light incidence direction L. The marginal ray light beam 9 has a multiplicity of light rays which form the marginal ray light beam 9. One of the light rays is a chief ray HS of the marginal ray light beam 9. The chief ray HS propagates at a first chief ray height H1 at the first lens L1, the first chief ray height H1 being a first distance between the optical axis OA and the chief ray HS at the first lens L1. For example, the first distance is the length of a first straight line which is aligned perpendicular to the optical axis OA and connects a first point P1 on the optical axis OA to a second point P2 on the chief ray HS at the first lens L1. In particular, the first distance can also be given as follows: As will be explained further below, the first lens L1 has a first surface and a second surface. The first surface is arranged on a first side of the first lens L1 facing away from the display unit 5. Further, the second surface is arranged on a second side of the first lens L1 facing the display unit 5. A first plane is arranged on the first surface of the first lens L1, the first straight line being located in the first plane. By way of example, the first plane is in contact with the first surface at at least one point. The chief ray HS propagates at a second chief ray height H2 at the display unit 5, the second chief ray height H2 being a second distance between the optical axis OA and the chief ray HS at the display unit 5. For example, the second distance is the length of a second straight line which is aligned perpendicular to the optical axis OA and connects a third point P3 on the optical axis OA to a fourth point P4 on the chief ray HS at the display unit 5. In particular, the second distance can also be given as follows: As will be explained further below, the display unit 5 has a surface. The surface of the display unit 5 is arranged on a side of the display unit 5 facing the first lens L1. Further, a second plane is arranged on the surface of the display unit 5. The second straight line is located in the second plane. By way of example, the second plane is in contact with the surface of the display unit 5 at at least one point.

[0166] The first chief ray height H1 has a greater value than the second chief ray height H2. By way of example, the first chief ray height H1 is approximately 10.1 mm and the second chief ray height H2 is approximately 5.3 mm. The invention is not restricted to the aforementioned magnitudes of the first chief ray height H1 and the second chief ray height H2. Rather, any first chief ray height H1 and any second chief ray height H2 which are suitable for the invention can be used for the invention.

[0167] The system data of the embodiment of the optical system 7 according to the invention in accordance with FIG. 11 emerge from the upper table in FIG. 12. The upper table in FIG. 12 is based on an incoming beam radius of 2.5 mm, an entrance angle of 27°, and an effective focal length of the optical system 7 according to the invention of −10.863 mm. The surface 0 denotes a surface at an infinite distance in front of the optical system 7 on the side of the eye 2 so that light can enter the optical system 7 in collimated fashion. Further, the surface 1 denotes the surface of the eye pupil of the eye 2. The first lens L1 has a surface 2 directed at the eye 2 and a surface 3 directed at the display unit 5. The second lens L2 has a surface 4 directed at the eye 2 and a surface 5 directed at the display unit 5. The third lens L3 has a surface 6 directed at the eye 2 and a surface 7 directed at the display unit 5. The fourth lens L4 has a surface 8 directed at the eye 2 and a surface 9 directed at the display unit 5. The fifth lens L5 has a surface 10 directed at the eye 2 and a surface 11 directed at the display unit 5. Further, the sixth lens L6 has a surface 12 directed at the eye 2 and a surface 13 directed at the display unit 5. The seventh lens L7 has a surface 14 directed at the eye 2. The eighth lens L8 has a surface 15 directed at the eye 2 and a surface 16 directed at the display unit 5. The surface 17 denotes the surface of the display unit 5. Further, the upper table in FIG. 12 specifies the radii of the individual surfaces and the thicknesses of the individual lenses of the optical system 7 according to the invention in accordance with FIG. 11, with the thickness of a lens being defined as the distance between a first vertex at the optical axis OA of a surface of the lens directed at the eye 2 and a second vertex at the optical axis OA of a surface of the lens directed at the display unit 5. A thickness between two of the aforementioned lenses denotes the distance between two vertices of two adjacent surfaces of two lenses.

[0168] The intermediate image ZB is arranged on the surface 5 of the second lens L2.

[0169] The upper table in FIG. 12 specifies the material of the individual lenses, the material specification corresponding to the nomenclature as used by the company OHARA. Moreover, the refractive indices are given for three different wavelengths of the light rays originating from the object O, specifically a wavelength 1 of 587.6 nm, a wavelength 2 of 435.8 nm, and a wavelength 3 of 643.8 nm. Further, the half diameters of the individual lenses and the refractive powers of the individual lenses are specified in the upper table in FIG. 12.

[0170] The surfaces 2 and 3 of the first lens L1 have an aspheric form. Further, the surfaces 8 and 9 of the fourth lens L4 have an aspheric form. The aspheric form of the aforementioned surfaces is determined by the asphere formula [1] mentioned above. The asphere coefficients and the conic constant are specified in the lower table in FIG. 12.

[0171] FIG. 13 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system 7 according to the invention in accordance with FIGS. 11 and 12. Shown are a sagittal contrast curve S (shown in solid lines) and a tangential contrast curve T (shown in dashed lines) for 20 line pairs per millimeter, 40 line pairs per millimeter, and 60 line pairs per millimeter.

[0172] In the embodiment of the optical system 7 according to the invention in accordance with FIGS. 11 to 13, the first lens L1 and the fourth lens L4, which each have a bi-aspheric form, have identical surface shapes. However, the first lens L1 and the fourth lens L4 are arranged on the optical axis OA rotated relative to one another along the optical axis OA. In other words, the first lens L1 is arranged on the optical axis OA with a first alignment and the fourth lens L4 is arranged on the optical axis OA with a second alignment. By way of example, the first alignment is rotated 180° with respect to the second alignment. In other words, the first alignment of the first lens L1 is a reflection of the second alignment of the fourth lens L4 in a straight line, which is aligned perpendicular to the optical axis OA in particular. The use of two identical lenses, specifically the first lens L1 and the fourth lens L4, reduces, for example, the production costs of the optical system 7 according to the invention, especially if this relates to aspheric lenses with high tooling costs.

[0173] In the embodiments of the optical system 7 according to the invention explained above, the intermediate image ZB in each case is in the immediate vicinity—for example at a distance of a few millimeters, in particular less than 3 mm—or even on an optical surface of one of the lenses of the embodiments of the optical system 7 according to the invention explained above. However, in a fifth embodiment of the optical system 7 according to the invention depicted in FIG. 14, it is possible to expose the intermediate image ZB, and so the latter is arranged neither in the direct vicinity of, nor on, an optical surface of any one of the lenses of the optical system 7 according to the invention. This significantly relaxes the cleanliness requirements with regard to possible scratches, inclusions and/or contamination on the lenses and lens surfaces adjacent to the intermediate image ZB.

[0174] The embodiment of the optical system 7 according to the invention in accordance with FIG. 14 has an optical axis OA, which corresponds to the optical axis OA of the piece of night vision equipment 1. An eyepiece 6 comprises a first lens group LG1 and a second lens group LG2. As seen counter to the light incidence direction L, the first lens group LG1 is arranged first along the optical axis OA, followed by the second lens group LG2. The intermediate image ZB is arranged between the first lens group LG1 and the second lens group LG2. Alternatively, the optical system 7 according to the invention in accordance with FIG. 14 can also be divided into three lens groups, specifically the first lens group LG1, a second lens group LG2′, and a third lens group LG3′. The second lens group LG2′ and the third lens group LG3′ are depicted with dashed lines in FIG. 14. As seen counter to the light incidence direction L, the first lens group LG1 is arranged first along the optical axis OA, followed by the second lens group LG2′ and then the third lens group LG3′. The intermediate image ZB is arranged between the first lens group LG1 and the second lens group LG2′.

[0175] The first lens group LG1 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 14 comprises a single lens in the form of a first lens L1. Consequently, no further optical units are provided in the first lens group LG1. The first lens L1 has positive refractive power.

[0176] The second lens group LG2 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 14 comprises a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6. As seen counter to the light incidence direction L, the second lens L2 is arranged first along the optical axis OA, followed by the third lens L3, then the fourth lens L4, then the fifth lens L5, and then the sixth lens L6. The second lens L2 has positive refractive power. The third lens L3 has negative refractive power. The fourth lens L4 has positive refractive power. The fifth lens L5 has positive refractive power and the sixth lens L6 has negative refractive power.

[0177] In the alternative embodiment of the optical system 7 according to the invention in accordance with FIG. 14, the second lens group LG2′ comprises the second lens L2 and the third lens L3. The third lens group LG3′ comprises the fourth lens L4, the fifth lens L5, and the sixth lens L6.

[0178] The first lens L1 and the second lens L2 have a bi-aspheric form. The third lens L3 is in the form of a meniscus lens. The fifth lens L5 and the sixth lens L6 form a cemented member.

[0179] In the embodiment of the optical system 7 according to the invention in accordance with FIG. 14, too, the first lens L1 forms the aforementioned lens unit of the optical system 7 according to the invention. As seen in the light incidence direction L, the display unit 5 is arranged first along the optical axis OA, followed by the first lens L1. No further optical unit of the optical system 7 according to the invention is arranged between the first lens L1 and an eye pupil of the eye 2.

[0180] A marginal ray light beam 9 emanates from an edge 8 of the display unit 5 and propagates to the first lens L1 in the light incidence direction L. The marginal ray light beam 9 has a multiplicity of light rays which form the marginal ray light beam 9. One of the light rays is a chief ray HS of the marginal ray light beam 9. The chief ray HS propagates at a first chief ray height H1 at the first lens L1, the first chief ray height H1 being a first distance between the optical axis OA and the chief ray HS at the first lens L1. For example, the first distance is the length of a first straight line which is aligned perpendicular to the optical axis OA and connects a first point P1 on the optical axis OA to a second point P2 on the chief ray HS at the first lens L1. In particular, the first distance can also be given as follows: As will be explained further below, the first lens L1 has a first surface and a second surface. The first surface is arranged on a first side of the first lens L1 facing away from the display unit 5. Further, the second surface is arranged on a second side of the first lens L1 facing the display unit 5. A first plane is arranged on the first surface of the first lens L1, the first straight line being located in the first plane. By way of example, the first plane is in contact with the first surface at at least one point. The chief ray HS propagates at a second chief ray height H2 at the display unit 5, the second chief ray height H2 being a second distance between the optical axis OA and the chief ray HS at the display unit 5. For example, the second distance is the length of a second straight line which is aligned perpendicular to the optical axis OA and connects a third point P3 on the optical axis OA to a fourth point P4 on the chief ray HS at the display unit 5. In particular, the second distance can also be given as follows: As will be explained further below, the display unit 5 has a surface. The surface of the display unit 5 is arranged on a side of the display unit 5 facing the first lens L1. Further, a second plane is arranged on the surface of the display unit 5. The second straight line is located in the second plane. By way of example, the second plane is in contact with the surface of the display unit 5 at at least one point.

[0181] The first chief ray height H1 has a greater value than the second chief ray height H2. By way of example, the first chief ray height H1 is approximately 9.7 mm and the second chief ray height H2 is approximately 5.3 mm. The invention is not restricted to the aforementioned magnitudes of the first chief ray height H1 and the second chief ray height H2. Rather, any first chief ray height H1 and any second chief ray height H2 which are suitable for the invention can be used for the invention.

[0182] The system data of the embodiment of the optical system 7 according to the invention in accordance with FIG. 14 emerge from the upper table in FIG. 15. The upper table in FIG. 15 is based on an incoming beam radius of 2.5 mm, an entrance angle of 27°, and an effective focal length of the optical system 7 according to the invention of −10.849 mm. The surface 0 denotes a surface at an infinite distance in front of the optical system 7 on the side of the eye 2 so that light can enter the optical system 7 in collimated fashion. Further, the surface 1 denotes the surface of the eye pupil of the eye 2. The first lens L1 has a surface 2 directed at the eye 2 and a surface 3 directed at the display unit 5. The second lens L2 has a surface 4 directed at the eye 2 and a surface 5 directed at the display unit 5. The third lens L3 has a surface 6 directed at the eye 2 and a surface 7 directed at the display unit 5. The fourth lens L4 has a surface 8 directed at the eye 2 and a surface 9 directed at the display unit 5. The fifth lens L5 has a surface 10 directed at the eye 2. Further, the sixth lens L6 has a surface 11 directed at the eye 2 and a surface 12 directed at the display unit 5. The surface 13 denotes the surface of the display unit 5. Further, the upper table in FIG. 15 specifies the radii of the individual surfaces and the thicknesses of the individual lenses of the optical system 7 according to the invention in accordance with FIG. 14, with the thickness of a lens being defined as the distance between a first vertex at the optical axis OA of a surface of the lens directed at the eye 2 and a second vertex at the optical axis OA of a surface of the lens directed at the display unit 5. A thickness between two of the aforementioned lenses denotes the distance between two vertices of two adjacent surfaces of two lenses.

[0183] The upper table in FIG. 15 specifies the material of the individual lenses, the material specification corresponding to the nomenclature as used by the company OHARA. Moreover, the refractive indices are given for three different wavelengths of the light rays originating from the object O, specifically a wavelength 1 of 587.6 nm, a wavelength 2 of 435.8 nm, and a wavelength 3 of 643.8 nm. Further, the half diameters of the individual lenses and the refractive powers of the individual lenses are specified in the upper table in FIG. 15.

[0184] The surfaces 2 and 3 of the first lens L1 have an aspheric form. Further, the surfaces 4 and 5 of the second lens L2 have an aspheric form. The aspheric form of the aforementioned surfaces is determined by the asphere formula [1] mentioned above. The asphere coefficients and the conic constant are specified in the lower table in FIG. 15.

[0185] FIG. 16 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system 7 according to the invention in accordance with FIGS. 14 and 15. Shown are a sagittal contrast curve S (shown in solid lines) and a tangential contrast curve T (shown in dashed lines) for 20 line pairs per millimeter, 40 line pairs per millimeter, and 60 line pairs per millimeter.

[0186] It is advantageous in the embodiment of the optical system 7 according to the invention in accordance with FIGS. 14 to 16 that, as seen counter to the light incidence direction L, the third lens L3, which is in the form of a meniscus lens, is arranged behind the second lens L2, which has a bi-aspheric form. This third lens L3 adopts the correction of the Petzval sum. This makes it possible for the Petzval sum to be no longer corrected by optical units located in the vicinity of the intermediate image ZB. Consequently, the intermediate image ZB can be exposed. The installation length of this embodiment of the optical system 7 according to the invention is 100 mm, for example. This makes it possible not to use any strongly refractive meniscus lenses between which the intermediate image ZB is arranged. Rather, it is sufficient to use the third lens L3 in the form of a meniscus lens, the latter adopting the correction of the Petzval sum.

[0187] FIG. 17 shows a sixth embodiment of the optical system 7 according to the invention. This embodiment of the optical system 7 according to the invention has an optical axis OA, which corresponds to the optical axis OA of the piece of night vision equipment 1. An eyepiece 6 comprises a first lens group LG1 and a second lens group LG2. As seen counter to the light incidence direction L, the first lens group LG1 is arranged first along the optical axis OA, followed by the second lens group LG2. The intermediate image ZB is arranged between the first lens group LG1 and the second lens group LG2.

[0188] The first lens group LG1 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 17 comprises a first lens L1 and a second lens L2. As seen counter to the light incidence direction, the first lens L1 is arranged first along the optical axis OA, followed by the second lens L2. The first lens L1 has positive refractive power. The second lens L2 has positive refractive power.

[0189] The second lens group LG2 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 17 comprises a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8. As seen counter to the light incidence direction L, the third lens L3 is arranged first along the optical axis OA, followed by the fourth lens L4, then the fifth lens L5, then the sixth lens L6, then the seventh lens L7, and then the eighth lens L8. The third lens L3 has positive refractive power. The fourth lens L4 has positive refractive power. The fifth lens L5 has negative refractive power. The sixth lens L6 has positive refractive power. The seventh lens L7 has positive refractive power and the eighth lens L8 has negative refractive power.

[0190] The first lens L1 has a bi-aspheric form. The second lens L2 and the third lens L3 are in the form of a meniscus lens. The fourth lens L4 has a bi-aspheric form. Further, the seventh lens L7 and the eighth lens L8 form a cemented member.

[0191] In the embodiment of the optical system 7 according to the invention in accordance with FIG. 17, too, the first lens L1 forms the aforementioned lens unit of the optical system 7 according to the invention. As seen in the light incidence direction L, the display unit 5 is arranged first along the optical axis OA, followed by the first lens L1 along the optical axis OA. No further optical unit of the optical system 7 according to the invention is arranged between the first lens L1 and an eye pupil of the eye 2.

[0192] A marginal ray light beam 9 emanates from an edge 8 of the display unit 5 and propagates to the first lens L1 in the light incidence direction L. The marginal ray light beam 9 has a multiplicity of light rays which form the marginal ray light beam 9. One of the light rays is a chief ray HS of the marginal ray light beam 9. The chief ray HS propagates at a first chief ray height H1 at the first lens L1, the first chief ray height H1 being a first distance between the optical axis OA and the chief ray HS at the first lens L1. For example, the first distance is the length of a first straight line which is aligned perpendicular to the optical axis OA and connects a first point P1 on the optical axis OA to a second point P2 on the chief ray HS at the first lens L1. In particular, the first distance can also be given as follows: As will be explained further below, the first lens L1 has a first surface and a second surface. The first surface is arranged on a first side of the first lens L1 facing away from the display unit 5. Further, the second surface is arranged on a second side of the first lens L1 facing the display unit 5. A first plane is arranged on the first surface of the first lens L1, the first straight line being located in the first plane. By way of example, the first plane is in contact with the first surface at at least one point. The chief ray HS propagates at a second chief ray height H2 at the display unit 5, the second chief ray height H2 being a second distance between the optical axis OA and the chief ray HS at the display unit 5. For example, the second distance is the length of a second straight line which is aligned perpendicular to the optical axis OA and connects a third point P3 on the optical axis OA to a fourth point P4 on the chief ray HS at the display unit 5. In particular, the second distance can also be given as follows: As will be explained further below, the display unit 5 has a surface. The surface of the display unit 5 is arranged on a side of the display unit 5 facing the first lens L1. Further, a second plane is arranged on the surface of the display unit 5. The second straight line is located in the second plane. By way of example, the second plane is in contact with the surface of the display unit 5 at at least one point.

[0193] The first chief ray height H1 has a greater value than the second chief ray height H2. By way of example, the first chief ray height H1 is approximately 9.7 mm and the second chief ray height H2 is approximately 5.3 mm. The invention is not restricted to the aforementioned magnitudes of the first chief ray height H1 and the second chief ray height H2. Rather, any first chief ray height H1 and any second chief ray height H2 which are suitable for the invention can be used for the invention.

[0194] The system data of the embodiment of the optical system 7 according to the invention in accordance with FIG. 17 emerge from the upper table in FIG. 18. The upper table in FIG. 18 is based on an incoming beam radius of 2.5 mm, an entrance angle of 27°, and an effective focal length of the optical system 7 according to the invention of −10.83 mm. The surface 0 denotes a surface at an infinite distance in front of the optical system 7 on the side of the eye 2 so that light can enter the optical system 7 in collimated fashion. Further, the surface 1 denotes the surface of the eye pupil of the eye 2. The first lens L1 has a surface 2 directed at the eye 2 and a surface 3 directed at the display unit 5. The second lens L2 has a surface 4 directed at the eye 2 and a surface 5 directed at the display unit 5. The third lens L3 has a surface 6 directed at the eye 2 and a surface 7 directed at the display unit 5. The fourth lens L4 has a surface 8 directed at the eye 2 and a surface 9 directed at the display unit 5. The fifth lens L5 has a surface 10 directed at the eye 2 and a surface 11 directed at the display unit 5. Further, the sixth lens L6 has a surface 12 directed at the eye 2 and a surface 13 directed at the display unit 5. The seventh lens L7 has a surface 14 directed at the eye 2. Moreover, the eighth lens L8 has a surface 15 directed at the eye 2 and a surface 16 directed at the display unit 5. The surface 17 denotes the surface of the display unit 5. Further, the upper table in FIG. 18 specifies the radii of the individual surfaces and the thicknesses of the individual lenses of the optical system 7 according to the invention in accordance with FIG. 17, with the thickness of a lens being defined as the distance between a first vertex at the optical axis OA of a surface of the lens directed at the eye 2 and a second vertex at the optical axis OA of a surface of the lens directed at the display unit 5. A thickness between two of the aforementioned lenses denotes the distance between two vertices of two adjacent surfaces of two lenses.

[0195] The upper table in FIG. 18 specifies the material of the individual lenses, the material specification corresponding to the nomenclature as used by the company OHARA. Moreover, the refractive indices are given for three different wavelengths of the light rays originating from the object O, specifically a wavelength 1 of 587.6 nm, a wavelength 2 of 435.8 nm, and a wavelength 3 of 643.8 nm. Further, the half diameters of the individual lenses and the refractive powers of the individual lenses are specified in the upper table in FIG. 18.

[0196] The surfaces 2 and 3 of the first lens L1 have an aspheric form. Further, the surfaces 8 and 9 of the fourth lens L4 have an aspheric form. The aspheric form of the aforementioned surfaces is determined by the asphere formula [1] mentioned above. The asphere coefficients and the conic constant are specified in the lower table in FIG. 18.

[0197] FIG. 19 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system 7 according to the invention in accordance with FIGS. 17 and 18. Shown are a sagittal contrast curve S (shown in solid lines) and a tangential contrast curve T (shown in dashed lines) for 20 line pairs per millimeter, 40 line pairs per millimeter, and 60 line pairs per millimeter.

[0198] The embodiment of the optical system 7 according to the invention in accordance with FIGS. 17 to 19 makes it possible to reduce the installation length of the embodiments of the optical system 7 according to the invention explained above from for example 100 mm to an installation length of for example 80 mm in this embodiment of the optical system 7 according to the invention, the installation length being measured from the pupil of the eye 2 to the display unit 5. On account of the shorter installation length, the individual lenses of the embodiment of the optical system 7 according to the invention in accordance with FIGS. 17 to 19 can have a greater refractive power than the lenses of the embodiments of the optical system 7 according to the invention explained further above. This could make it more difficult to correct the Petzval sum. However, the latter is corrected, for example, by virtue of the second lens L2 and the third lens L3 each being in the form of a meniscus lens, between which the intermediate image ZB is arranged. The shortened installation length of this embodiment of the optical system 7 according to the invention leads to an increased number of lenses, specifically the eight lenses L1 to L8 mentioned above, of which two lenses have a bi-aspheric form, specifically the first lens L1 and the fourth lens L4.

[0199] The number of lenses should sometimes be minimized in an optical system 7 according to the invention. This is possible with a seventh embodiment in accordance with FIG. 20 of the optical system 7 according to the invention. In this embodiment of the optical system 7 according to the invention, the intermediate image ZB is exposed, and so the latter is arranged neither in the direct vicinity of, nor on, an optical surface of any one of the lenses of the optical system 7 according to the invention. The embodiment of the optical system 7 according to the invention in accordance with FIG. 20 has an optical axis OA, which corresponds to the optical axis OA of the piece of night vision equipment 1. An eyepiece 6 comprises a first lens group LG1 and a second lens group LG2. As seen counter to the light incidence direction L, the first lens group LG1 is arranged first along the optical axis OA, followed by the second lens group LG2. The intermediate image ZB is arranged between the first lens group LG1 and the second lens group LG2.

[0200] The first lens group LG1 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 20 comprises a single lens in the form of a first lens L1. Consequently, no further optical units are provided in the first lens group LG1. The first lens L1 has positive refractive power.

[0201] The second lens group LG2 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 20 comprises a second lens L2, a third lens L3, and a fourth lens L4. As seen counter to the light incidence direction L, the second lens L2 is arranged first along the optical axis OA, followed by the third lens L3 and then the fourth lens L4. The second lens L2 has positive refractive power. The third lens L3 has positive refractive power. The fourth lens L4 has negative refractive power.

[0202] The embodiment of the optical system 7 according to the invention in accordance with FIG. 20 has a total of only 4 lenses. The first lens L1, the second lens L2, and the third lens L3 have a bi-aspheric form.

[0203] In the embodiment of the optical system 7 according to the invention in accordance with FIG. 20, too, the first lens L1 forms the aforementioned lens unit of the optical system 7 according to the invention. As seen in the light incidence direction L, the display unit 5 is arranged first along the optical axis OA, followed by the first lens L1. No further optical unit of the optical system 7 is arranged between the first lens L1 and an eye pupil of the eye 2.

[0204] A marginal ray light beam 9 emanates from an edge 8 of the display unit 5 and propagates to the first lens L1 in the light incidence direction L. The marginal ray light beam 9 has a multiplicity of light rays which form the marginal ray light beam 9. One of the light rays is a chief ray HS of the marginal ray light beam 9. The chief ray HS propagates at a first chief ray height H1 at the first lens L1, the first chief ray height H1 being a first distance between the optical axis OA and the chief ray HS at the first lens L1. For example, the first distance is the length of a first straight line which is aligned perpendicular to the optical axis OA and connects a first point P1 on the optical axis OA to a second point P2 on the chief ray HS at the first lens L1. In particular, the first distance can also be given as follows: As will be explained further below, the first lens L1 has a first surface and a second surface. The first surface is arranged on a first side of the first lens L1 facing away from the display unit 5. Further, the second surface is arranged on a second side of the first lens L1 facing the display unit 5. A first plane is arranged on the first surface of the first lens L1, the first straight line being located in the first plane. By way of example, the first plane is in contact with the first surface at at least one point. The chief ray HS propagates at a second chief ray height H2 at the display unit 5, the second chief ray height H2 being a second distance between the optical axis OA and the chief ray HS at the display unit 5. For example, the second distance is the length of a second straight line which is aligned perpendicular to the optical axis OA and connects a third point P3 on the optical axis OA to a fourth point P4 on the chief ray HS at the display unit 5. In particular, the second distance can also be given as follows: As will be explained further below, the display unit 5 has a surface. The surface of the display unit 5 is arranged on a side of the display unit 5 facing the first lens L1. Further, a second plane is arranged on the surface of the display unit 5. The second straight line is located in the second plane. By way of example, the second plane is in contact with the surface of the display unit 5 at at least one point.

[0205] The first chief ray height H1 has a greater value than the second chief ray height H2. By way of example, the first chief ray height H1 is approximately 13.4 mm and the second chief ray height H2 is approximately 5.3 mm. The invention is not restricted to the aforementioned magnitudes of the first chief ray height H1 and the second chief ray height H2. Rather, any first chief ray height H1 and any second chief ray height H2 which are suitable for the invention can be used for the invention.

[0206] The system data of the embodiment of the optical system 7 according to the invention in accordance with FIG. 20 emerge from the upper table in FIG. 21. The upper table in FIG. 21 is based on an incoming beam radius of 2.5 mm, an entrance angle of 27°, and an effective focal length of the optical system 7 according to the invention of −10.931 mm. The surface 0 denotes a surface at an infinite distance in front of the optical system 7 on the side of the eye 2 so that light can enter the optical system 7 in collimated fashion. Further, the surface 1 denotes the surface of the eye pupil of the eye 2. The first lens L1 has a surface 2 directed at the eye 2 and a surface 3 directed at the display unit 5. The second lens L2 has a surface 4 directed at the eye 2 and a surface 5 directed at the display unit 5. The third lens L3 has a surface 6 directed at the eye 2 and a surface 7 directed at the display unit 5. The fourth lens L4 has a surface 8 directed at the eye 2 and a surface 9 directed at the display unit 5. The surface 10 denotes the surface of the display unit 5. Further, the upper table in FIG. 21 specifies the radii of the individual surfaces and the thicknesses of the individual lenses of the optical system 7 according to the invention in accordance with FIG. 20, with the thickness of a lens being defined as the distance between a first vertex at the optical axis OA of a surface of the lens directed at the eye 2 and a second vertex at the optical axis OA of a surface of the lens directed at the display unit 5. A thickness between two of the aforementioned lenses denotes the distance between two vertices of two adjacent surfaces of two lenses.

[0207] The upper table in FIG. 21 specifies the material of the individual lenses, the material specification corresponding to the nomenclature as used by the company OHARA. Moreover, the refractive indices are given for three different wavelengths of the light rays originating from the object O, specifically a wavelength 1 of 587.6 nm, a wavelength 2 of 435.8 nm, and a wavelength 3 of 643.8 nm. Further, the half diameters of the individual lenses and the refractive powers of the individual lenses are specified in the upper table in FIG. 21.

[0208] The surfaces 2 and 3 of the first lens L1 have an aspheric form. Further, the surfaces 4 and 5 of the second lens L2 have an aspheric form. Moreover, the surfaces 6 and 7 of the third lens L3 have an aspheric form. The aspheric form of the aforementioned surfaces is determined by the asphere formula [1] mentioned above. The asphere coefficients and the conic constant are specified in the lower table in FIG. 21.

[0209] FIG. 22 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system 7 according to the invention in accordance with FIGS. 20 and 21. Shown are a sagittal contrast curve S (shown in solid lines) and a tangential contrast curve T (shown in dashed lines) for 20 line pairs per millimeter, 40 line pairs per millimeter, and 60 line pairs per millimeter.

[0210] The installation length of the embodiment of the optical system 7 according to the invention in accordance with FIGS. 20 to 22 is 200 mm, for example. On account of this installation length, the provision of high refractive powers for the individual lenses is no longer mandatory. This allows a simple correction of the Petzval sum. By way of example, the correction of the Petzval sum is provided by the fourth lens L4. In addition or as an alternative thereto, provision is made for the fourth lens L4 to carry out a correction of the longitudinal chromatic aberration. In particular, provision is made for the fourth lens L4 to be formed from a flint glass.

[0211] In order to use the optical system 7 according to the invention, for example in a refractor or in a pair of field glasses, it is desirable to generate, for example, a telecentric embodiment of an image space. In other words, the chief rays of all light beams should propagate parallel to the optical axis OA. This can be provided, for example, by an eighth embodiment of the optical system 7 according to the invention in accordance with FIG. 23.

[0212] The embodiment of the optical system 7 according to the invention in accordance with FIG. 23 has an optical axis OA, which corresponds to the optical axis OA of the piece of night vision equipment 1. An eyepiece 6 comprises a first lens group LG1 and a second lens group LG2. As seen counter to the light incidence direction L, the first lens group LG1 is arranged first along the optical axis OA, followed by the second lens group LG2. The intermediate image ZB is arranged between the first lens group LG1 and the second lens group LG2.

[0213] The first lens group LG1 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 23 comprises a single lens in the form of a first lens L1. Consequently, no further optical units are provided in the first lens group LG1. The first lens L1 has positive refractive power.

[0214] The second lens group LG2 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 23 comprises a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens L6. As seen counter to the light incidence direction L, the second lens L2 is arranged first along the optical axis OA, followed by the third lens L3, then the fourth lens L4, then the fifth lens L5, and then the sixth lens L6. The second lens L2 has positive refractive power. The third lens L3 has negative refractive power. The fourth lens L4 has negative refractive power. The fifth lens L5 has positive refractive power. The sixth lens L6 also has positive refractive power.

[0215] In the embodiment of the optical system 7 according to the invention in accordance with FIG. 23, the first lens L1 and the second lens L2 have a bi-aspheric form. Further, a surface of the sixth lens L6 has an aspheric form. The fourth lens L4 and the fifth lens L5 form a cemented member.

[0216] In the embodiment of the optical system 7 according to the invention in accordance with FIG. 23, too, the first lens L1 forms the aforementioned lens unit of the optical system 7 according to the invention. As seen in the light incidence direction L, the display unit 5 is arranged first along the optical axis OA, followed by the first lens L1. No further optical unit of the optical system 7 according to the invention is arranged between the first lens L1 and an eye pupil of the eye 2.

[0217] A marginal ray light beam 9 emanates from an edge 8 of the display unit 5 and propagates to the first lens L1 in the light incidence direction L. The marginal ray light beam 9 has a multiplicity of light rays which form the marginal ray light beam 9. One of the light rays is a chief ray HS of the marginal ray light beam 9. The chief ray HS propagates at a first chief ray height H1 at the first lens L1, the first chief ray height H1 being a first distance between the optical axis OA and the chief ray HS at the first lens L1. For example, the first distance is the length of a first straight line which is aligned perpendicular to the optical axis OA and connects a first point P1 on the optical axis OA to a second point P2 on the chief ray HS at the first lens L1. In particular, the first distance can also be given as follows: As will be explained further below, the first lens L1 has a first surface and a second surface. The first surface is arranged on a first side of the first lens L1 facing away from the display unit 5. Further, the second surface is arranged on a second side of the first lens L1 facing the display unit 5. A first plane is arranged on the first surface of the first lens L1, the first straight line being located in the first plane. By way of example, the first plane is in contact with the first surface at at least one point. The chief ray HS propagates at a second chief ray height H2 at the display unit 5, the second chief ray height H2 being a second distance between the optical axis OA and the chief ray HS at the display unit 5. For example, the second distance is the length of a second straight line which is aligned perpendicular to the optical axis OA and connects a third point P3 on the optical axis OA to a fourth point P4 on the chief ray HS at the display unit 5. In particular, the second distance can also be given as follows: As will be explained further below, the display unit 5 has a surface. The surface of the display unit 5 is arranged on a side of the display unit 5 facing the first lens L1. Further, a second plane is arranged on the surface of the display unit 5. The second straight line is located in the second plane. By way of example, the second plane is in contact with the surface of the display unit 5 at at least one point.

[0218] The first chief ray height H1 has a greater value than the second chief ray height H2. By way of example, the first chief ray height H1 is approximately 9.1 mm and the second chief ray height H2 is approximately 5.3 mm. The invention is not restricted to the aforementioned magnitudes of the first chief ray height H1 and the second chief ray height H2. Rather, any first chief ray height H1 and any second chief ray height H2 which are suitable for the invention can be used for the invention.

[0219] The system data of the embodiment of the optical system 7 according to the invention in accordance with FIG. 23 emerge from the upper table in FIG. 24. The upper table in FIG. 24 is based on an incoming beam radius of 2.5 mm, an entrance angle of 27°, and an effective focal length of the optical system 7 according to the invention of −10.849 mm. The surface 0 denotes a surface at an infinite distance in front of the optical system 7 on the side of the eye 2 so that light can enter the optical system 7 in collimated fashion. Further, the surface 1 denotes the surface of the eye pupil of the eye 2. The first lens L1 has a surface 2 directed at the eye 2 and a surface 3 directed at the display unit 5. The second lens L2 has a surface 4 directed at the eye 2 and a surface 5 directed at the display unit 5. The third lens L3 has a surface 6 directed at the eye 2 and a surface 7 directed at the display unit 5. The fourth lens L4 has a surface 8 directed at the eye 2. The fifth lens L5 has a surface 9 directed at the eye 2 and a surface 10 directed at the display unit 5. The sixth lens L6 has a surface 11 directed at the eye 2 and a surface 12 directed at the display unit 5. The surface 13 denotes the surface of the display unit 5. Further, the upper table in FIG. 24 specifies the radii of the individual surfaces and the thicknesses of the individual lenses of the optical system 7 according to the invention in accordance with FIG. 23, with the thickness of a lens being defined as the distance between a first vertex at the optical axis OA of a surface of the lens directed at the eye 2 and a second vertex at the optical axis OA of a surface of the lens directed at the display unit 5. A thickness between two of the aforementioned lenses denotes the distance between two vertices of two adjacent surfaces of two lenses.

[0220] The upper table in FIG. 24 specifies the material of the individual lenses, the material specification corresponding to the nomenclature as used by the company OHARA. Moreover, the refractive indices are given for three different wavelengths of the light rays originating from the object O, specifically a wavelength 1 of 587.6 nm, a wavelength 2 of 435.8 nm, and a wavelength 3 of 643.8 nm. Further, the half diameters of the individual lenses and the refractive powers of the individual lenses are specified in the upper table in FIG. 24.

[0221] The surfaces 2 and 3 of the first lens L1 have an aspheric form. Further, the surfaces 4 and 5 of the second lens L2 have an aspheric form. Moreover, the surface 11 of the sixth lens L6 has an aspheric form. The aspheric form of the aforementioned surfaces is determined by the asphere formula [1] mentioned above. The asphere coefficients and the conic constant are specified in the lower table in FIG. 24.

[0222] The Petzval sum is corrected by the meniscus-shaped third lens L3 and the meniscus-shaped cemented member consisting of the fourth lens L4 and the fifth lens L5.

[0223] FIG. 25 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system 7 according to the invention in accordance with FIGS. 23 and 24. Shown are a sagittal contrast curve S (shown in solid lines) and a tangential contrast curve T (shown in dashed lines) for 20 line pairs per millimeter, 40 line pairs per millimeter, and 60 line pairs per millimeter.

[0224] A ninth embodiment of the optical system 7 according to the invention, which is used for example in a refractor or in a pair of field glasses, is depicted in FIG. 26. This embodiment of the optical system 7 according to the invention also generates a telecentric embodiment of an image space.

[0225] The embodiment of the optical system 7 according to the invention in accordance with FIG. 26 has an optical axis OA, which corresponds to the optical axis OA of the piece of night vision equipment 1. An eyepiece 6 comprises a first lens group LG1 and a second lens group LG2. As seen counter to the light incidence direction L, the first lens group LG1 is arranged first along the optical axis OA, followed by the second lens group LG2. The intermediate image ZB is arranged between the first lens group LG1 and the second lens group LG2.

[0226] The first lens group LG1 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 26 comprises a single lens in the form of a first lens L1. Consequently, no further optical units are provided in the first lens group LG1. The first lens L1 has positive refractive power.

[0227] The second lens group LG2 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 26 comprises a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. As seen counter to the light incidence direction L, the second lens L2 is arranged first along the optical axis OA, followed by the third lens L3, then the fourth lens L4, then the fifth lens L5, then the sixth lens L6, and then the seventh lens L7. The second lens L2 has positive refractive power. The third lens L3 has negative refractive power. The fourth lens L4 has negative refractive power. The fifth lens L5 has positive refractive power. The sixth lens L6 has positive refractive power. The seventh lens L7 also has positive refractive power.

[0228] In the embodiment of the optical system 7 according to the invention in accordance with FIG. 26, the first lens L1 and the second lens L2 have a bi-aspheric form. The fourth lens L4 and the fifth lens L5 form a cemented member.

[0229] In the embodiment of the optical system according to the invention in accordance with FIG. 26, too, the first lens L1 forms the aforementioned lens unit of the optical system 7 according to the invention. As seen in the light incidence direction L, the display unit 5 is arranged first along the optical axis OA, followed by the first lens L1 along the optical axis OA. No further optical unit of the optical system 7 according to the invention is arranged between the first lens L1 and an eye pupil of the eye 2.

[0230] A marginal ray light beam 9 emanates from an edge 8 of the display unit 5 and propagates to the first lens L1 in the light incidence direction L. The marginal ray light beam 9 has a multiplicity of light rays which form the marginal ray light beam 9. One of the light rays is a chief ray HS of the marginal ray light beam 9. The chief ray HS propagates at a first chief ray height H1 at the first lens L1, the first chief ray height H1 being a first distance between the optical axis OA and the chief ray HS at the first lens L1. For example, the first distance is the length of a first straight line which is aligned perpendicular to the optical axis OA and connects a first point P1 on the optical axis OA to a second point P2 on the chief ray HS at the first lens L1. In particular, the first distance can also be given as follows: As will be explained further below, the first lens L1 has a first surface and a second surface. The first surface is arranged on a first side of the first lens L1 facing away from the display unit 5. Further, the second surface is arranged on a second side of the first lens L1 facing the display unit 5. A first plane is arranged on the first surface of the first lens L1, the first straight line being located in the first plane. By way of example, the first plane is in contact with the first surface at at least one point. The chief ray HS propagates at a second chief ray height H2 at the display unit 5, the second chief ray height H2 being a second distance between the optical axis OA and the chief ray HS at the display unit 5. For example, the second distance is the length of a second straight line which is aligned perpendicular to the optical axis OA and connects a third point P3 on the optical axis OA to a fourth point P4 on the chief ray HS at the display unit 5. In particular, the second distance can also be given as follows: As will be explained further below, the display unit 5 has a surface. The surface of the display unit 5 is arranged on a side of the display unit 5 facing the first lens L1. Further, a second plane is arranged on the surface of the display unit 5. The second straight line is located in the second plane. By way of example, the second plane is in contact with the surface of the display unit 5 at at least one point.

[0231] The first chief ray height H1 has a greater value than the second chief ray height H2. By way of example, the first chief ray height H1 is approximately 9.3 mm and the second chief ray height H2 is approximately 5.3 mm. The invention is not restricted to the aforementioned magnitudes of the first chief ray height H1 and the second chief ray height H2. Rather, any first chief ray height H1 and any second chief ray height H2 which are suitable for the invention can be used for the invention.

[0232] The system data of the embodiment of the optical system 7 according to the invention in accordance with FIG. 26 emerge from the upper table in FIG. 27. The upper table in FIG. 27 is based on an incoming beam radius of 2.5 mm, an entrance angle of 27°, and an effective focal length of the optical system 7 according to the invention of −10.882 mm. The surface 0 denotes a surface at an infinite distance in front of the optical system 7 on the side of the eye 2 so that light can enter the optical system 7 in collimated fashion. Further, the surface 1 denotes the surface of the eye pupil of the eye 2. The first lens L1 has a surface 2 directed at the eye 2 and a surface 3 directed at the display unit 5. The second lens L2 has a surface 4 directed at the eye 2 and a surface 5 directed at the display unit 5. The third lens L3 has a surface 6 directed at the eye 2 and a surface 7 directed at the display unit 5. The fourth lens L4 has a surface 8 directed at the eye 2. The fifth lens L5 has a surface 9 directed at the eye 2 and a surface 10 directed at the display unit 5. The sixth lens L6 has a surface 11 directed at the eye 2 and a surface 12 directed at the display unit 5. The seventh lens L7 has a surface 13 directed at the eye 2 and a surface 14 directed at the display unit 5. The surface 15 denotes the surface of the display unit 5. Further, the upper table in FIG. 27 specifies the radii of the individual surfaces and the thicknesses of the individual lenses of the optical system 7 according to the invention in accordance with FIG. 26, with the thickness of a lens being defined as the distance between a first vertex at the optical axis OA of a surface of the lens directed at the eye 2 and a second vertex at the optical axis OA of a surface of the lens directed at the display unit 5. A thickness between two of the aforementioned lenses denotes the distance between two vertices of two adjacent surfaces of two lenses.

[0233] The upper table in FIG. 27 specifies the material of the individual lenses, the material specification corresponding to the nomenclature as used by the company OHARA. Moreover, the refractive indices are given for three different wavelengths of the light rays originating from the object O, specifically a wavelength 1 of 587.6 nm, a wavelength 2 of 435.8 nm, and a wavelength 3 of 643.8 nm. Further, the half diameters of the individual lenses and the refractive powers of the individual lenses are specified in the upper table in FIG. 27.

[0234] The surfaces 2 and 3 of the first lens L1 have an aspheric form. Further, the surfaces 4 and 5 of the second lens L2 have an aspheric form. The aspheric form of the aforementioned surfaces is determined by the asphere formula [1] mentioned above. The asphere coefficients and the conic constant are specified in the lower table in FIG. 27.

[0235] The correction of the Petzval sum is provided by the seventh lens L7.

[0236] FIG. 28 shows curves of the modulation transfer function (MTF) as a function of the object height for the embodiment of the optical system 7 according to the invention in accordance with FIGS. 26 and 27. Shown are a sagittal contrast curve S (shown in solid lines) and a tangential contrast curve T (shown in dashed lines) for 20 line pairs per millimeter, 40 line pairs per millimeter, and 60 line pairs per millimeter.

[0237] The above-described embodiments of the optical system 7 according to the invention are designed as a dioptric system. In other words, the optical system 7 according to the invention comprises only lenses. Additionally or alternatively, provision can be made for the optical system 7 according to the invention to comprise at least one planar folding mirror, which in particular has no optical refractive power. Thus, this embodiment of the optical system 7 according to the invention likewise is a dioptric system.

[0238] In the above-described embodiments of the optical system 7 according to the invention, the distance between the eye pupil of the eye 2 and the first lens L1 is greater than the focal length of the corresponding optical system 7 according to the invention. By way of example, the distance from the eye pupil of the eye 2 to the first lens L1 is at least 1.25 times greater than the focal length of the optical system 7 according to the invention. As an alternative thereto, the distance from the eye pupil of the eye 2 to the first lens L1 is at least 1.5 times greater than the focal length of the optical system 7 according to the invention. Further additionally or in an alternative thereto, the distance from the eye pupil of the eye 2 to the first lens L1 is at least 1.7 times greater than one focal length of the optical system 7 according to the invention.

[0239] The embodiments of the optical system 7 according to the invention enable comfortable viewing, in particular for a spectacle wearer, since the eyepiece 6 of the optical system 7 according to the invention has both a large pupil distance (for example, approx. 18 mm) for a pupil of the eye with a diameter of 5 mm and a large half field angle (for example, approx. 27°). Further, the optical system 7 according to the invention enables an erection of an image without the arrangement of a further inversion system in the optical system 7 according to the invention being mandatory.

[0240] FIG. 29 shows a further embodiment of the optical system 7 according to the invention, which has an optical axis OA that corresponds to the optical axis OA of the piece of night vision equipment 1. However, by all means, this embodiment of the optical system 7 can also be used in a light microscope, a refractor, a pair of field glasses or in a piece of medical operation equipment. An eyepiece 6 comprises a first lens group LG1 and a second lens group LG2. As seen counter to the light incidence direction L, the first lens group LG1 is arranged first along the optical axis OA, followed by the second lens group LG2. An intermediate pupil ZP is arranged between the first lens group LG1 and the second lens group LG2.

[0241] The first lens group LG1 of the embodiment of the optical system 7 according to the invention in accordance with FIG. 29 comprises a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7. As seen counter to the light incidence direction L, the first lens L1 is arranged first along the optical axis OA, followed by the second lens L2, then the third lens L3, then the fourth lens L4, then the fifth lens L5, then the sixth lens L6, and then the seventh lens L7.

[0242] The second lens group LG2 of the embodiment of the optical system 7 according to the invention in FIG. 29 comprises an eighth lens L8, a ninth lens L9, a tenth lens L10, an eleventh lens L11, a twelfth lens L12, a thirteenth lens L13, and a fourteenth lens L14. As seen counter to the light incidence direction L, the eighth lens L8 is arranged first along the optical axis OA, followed by the ninth lens L9, then the tenth lens L10, then the eleventh lens L11, then the twelfth lens L12, then the thirteenth lens L13, and then the fourteenth lens L14.

[0243] The first lens group LG1 may also be referred to as a pupil relay unit. The second lens group LG2 may also be referred to as further optical assembly. A lens group is understood to mean a group containing at least one optical assembly, for example in the form of a lens. In particular, provision is made for the lens group to comprise only a single lens or a plurality of lenses.

[0244] No further optical unit of the optical system 7 is arranged between the first lens L1 and an eye pupil of the eye 2. The distance between the pupil of the eye and the first lens L1 is approx. 18.4 mm. Here, this value has been chosen so that a particularly preferred distance of approx. 18 mm also arises at the edge of the slightly concavely shaped front side of the first lens L1.

[0245] In this embodiment of the optical system 7, the display unit 5 is designed so that, for a display with a visual field with a diameter of 9.6 mm, a large apparent visual field diameter of 600 arises. By way of example, the display unit 5 comprises a 1 inch display with a resolution of 2096×2096 pixels, into which it is possible to write a circular field of vision with a diameter of 18.4 mm. This means that the display can display an image circle with a radius of 9.2 mm, with the remaining pixels being blanked. The image circle is imaged by the eyepiece 6 into the circular apparent field of vision of the observer with 600 diameter, possibly taking account of a pincushion distortion.

[0246] The paraxial focal length of the eyepiece 6 in this embodiment of the optical system 7 is 17.55 mm. Further, a pre-definable spatial region B is arranged at the eyepiece 6, in which spatial region the eye 2 is able to move in such a way without a pre-definable threshold value of an image quality of an image representation of the image produced by the eyepiece 6 being undershot. The pre-definable region B is the eye box, which has already been defined above. As seen in the direction of the spatial region B starting from the display unit 5, the display unit 5 is arranged first in the light incidence direction L, followed by the eyepiece 6 and then the spatial region B.

[0247] As already explained above, the intermediate pupil ZP is arranged between the first lens group LG1 and the second lens group LG2. The second lens group LG2 is designed to image the image displayed by the display unit 5 into the intermediate pupil ZP. Moreover, the first lens group LG1 is designed to image the image arranged in the intermediate pupil ZP into the spatial region B. The intermediate pupil ZP and the spatial region B are conjugate to one another.

[0248] An aperture unit BE is arranged at the intermediate pupil ZP. In other words, the aperture unit BE is arranged at the location of the intermediate pupil ZP. Expressed differently yet again, the aperture unit BE is arranged in a plane at the location of the intermediate pupil ZP. By way of example, the aperture unit BE is embodied as a mechanical aperture unit. In particular, provision is made for the aperture unit BE to be provided with a circular aperture, with a size of the aperture being fixedly predetermined or adjustable. In addition or as an alternative thereto, provision is made for the aperture unit BE to be provided with an elliptical aperture, with a size of the aperture being fixedly predetermined or adjustable. An elliptical aperture is advantageous for the provision of an eye box which has different extents vertically and horizontally. In the case of equipment for binocular observation (e.g., a pair of field glasses or a microscope with a binocular eyepiece) in particular, an eye box with a horizontal (lateral) extent that is greater than the vertical extent of the eye box is often advantageous since, in addition to the unavoidable head movement of the observer, additional play is desirable for taking account of the interpupillary distances, which are different for different people, between a right eye and a left eye. Explicit reference is made to the fact that the invention is not restricted to the aforementioned aperture shapes. Instead, the aperture may have any shape that is suitable for the invention and/or required for a desired shape of the eye box.

[0249] The first lens group LG1 has an intermediate caustic ZB, which is arranged between the third lens L3 and the fourth lens L4 in this embodiment of the further optical system 7 according to the invention. The intermediate caustic ZB may be a plane and corrected intermediate image. However, the intermediate caustic ZB need not be in the form of the above-described intermediate image. The intermediate caustic can facilitate the design of an eyepiece 6 with a large eye box and, at the same time, a short focal length.

[0250] The embodiment of the further optical system 7 according to FIG. 29 is designed for a maximum eye box with a 7 mm diameter. This means that the observer with an assumed eye pupil with a 3 mm diameter (the assumption being that of an eye adapted to moderate brightness) can move an eye position arranged on the optical axis OA by up to 2 mm to each side before any vignetting occurs. To this end, the aperture unit BE has a circular aperture with a diameter of approx. 20 mm. A smaller aperture can also be used in further embodiments, in order to admit less vignetting for a laterally off-centered eye pupil.

[0251] The system data of the embodiment of the further optical system 7 according to the invention in accordance with FIG. 29 emerge from the table in FIG. 38. The surface 0 denotes a surface at an infinite distance in front of the optical system 7 on the side of the eye 2 so that light can enter the optical system 7 in collimated fashion. Further, the surface 1 denotes the surface of the eye pupil of the eye 2. The first lens L1 has a surface 2 directed at the eye 2 and a surface 3 directed at the display unit 5. The second lens L2 has a surface 4 directed at the eye 2 and a surface 5 directed at the display unit 5. The third lens L3 has a surface 6 directed at the eye 2 and a surface 7 directed at the display unit 5. The intermediate caustic is denoted by the surface 8. The fourth lens L4 has a surface 9 directed at the eye 2 and a surface 10 directed at the display unit 5. The fifth lens L5 has a surface 11 directed at the eye 2 and a surface 12 directed at the display unit 5. Further, the sixth lens L6 has a surface 13 directed at the eye 2 and a surface 14 directed at the display unit 5. The seventh lens L7 has a surface 15 directed at the eye 2 and a surface 16 directed at the display unit 5. The intermediate pupil is denoted by the surface 17. The eighth lens L8 has a surface 18 directed at the eye 2 and a surface 19 directed at the display unit 5. The ninth lens L9 has a surface 20 directed at the eye 2. The tenth lens L10 has a surface 21 directed at the eye 2 and a surface 22 directed at the display unit 5. The eleventh lens L11 has a surface 23 directed at the eye 2. Further, the twelfth lens L12 has a surface 24 directed at the eye 2 and a surface 25 directed at the display unit 5. The thirteenth lens L13 has a surface 26 directed at the eye 2 and a surface 27 directed at the display unit 5. Further, the fourteenth lens L14 has a surface 28 directed at the eye 2 and a surface 29 directed at the display unit 5. The surface 30 denotes the surface of the display unit 5.

[0252] Further, the table in FIG. 38 specifies the radii of the individual surfaces and the thicknesses of the individual lenses of the further optical system 7 according to the invention in accordance with FIG. 29, with the thickness of a lens being defined as the distance between a first vertex at the optical axis OA of a surface of the lens directed at the eye 2 and a second vertex at the optical axis OA of a surface of the lens facing the display unit 5. A thickness between two of the aforementioned lenses denotes the distance between two vertices of two adjacent surfaces of two lenses.

[0253] The table in FIG. 38 specifies the material of the individual lenses, the material specification corresponding to the nomenclature as used by the company OHARA. However, the fifth lens L5 and the sixth lens L6 are formed from a material from the company Schott. Further, the half diameter of the individual lenses is specified in the table in FIG. 38. Some surfaces have an aspheric form. The aspheric form of these surfaces is determined by the asphere formula [1] mentioned above. The asphere coefficients and the conic constant are specified in the table in FIG. 39.

[0254] For the further optical system 7 according to the invention with a maximum eye box with a diameter of 7 mm, FIG. 30 shows a schematic representation of the aperture aberration (longitudinal spherical aberration), the tangential and sagittal image surface positions (astigmatic field curves), and the relative distortion. For the further optical system 7 according to the invention with a centered eye pupil with a diameter of 3 mm, FIG. 31, by contrast, shows a schematic representation of the aperture aberration (longitudinal spherical aberration), the tangential and sagittal image surface positions (astigmatic field curves), and the relative distortion.

[0255] For the further optical system 7 according to the invention with a centered eye pupil with a diameter of 3 mm, FIG. 32 shows a schematic representation of the transverse aberrations. For the further optical system 7 according to the invention with an eye pupil with a diameter of 3 mm off-centered relative to the optical axis OA by 1 mm, FIG. 33, by contrast, shows a schematic representation of the transverse aberrations. For the further optical system 7 according to the invention with an eye pupil with a diameter of 3 mm off-centered relative to the optical axis OA by 2 mm, FIG. 34 further shows a schematic representation of the transverse aberrations.

[0256] FIG. 35 shows curves of the modulation transfer function (MTF) of the eyepiece 6 up to 80 line pairs/mm at the display unit 5 for different visual field angles for a centered pupil of the eye with a diameter of 3 mm. By contrast, FIG. 36 shows curves of the modulation transfer function (MTF) of the eyepiece 6 up to 80 line pairs/mm at the display unit 5 for different visual field angles for a pupil of the eye with a diameter of 3 mm laterally off-centered relative to the optical axis OA by 1 mm. Further, FIG. 37 shows curves of the modulation transfer function (MTF) of the eyepiece 6 up to 80 line pairs/mm at the display unit 5 for different visual field angles for a pupil of the eye with a diameter of 3 mm laterally off-centered to the optical axis OA by 2 mm.

[0257] In view of the use in field glasses, the eyepiece 6 may have a pincushion distortion of 5.3% at the edge of the visual field. This value of the distortion and the curve over the image field have been chosen such that the “globe effect” (cf. publication by H. Merlitz, “Distortion of binoculars revisited: Does the sweet spot exist?”, J. Opt. Soc. Am. A/Volume 27, No. 1/January 2010) is minimized in the case of lateral panning. The “globe effect” is a known and empirically well-validated effect, which is however still discussed in relation to its precise physiological and perception-psychological causes, in the case of which the visual impression of the observer would carry out a type of rolling movement on a spherical surface when a pair of field glasses are panned laterally, for example when inspecting the night sky. Observing what is known as the Merlitz condition, which is under discussion in the publication above, with an empirically determined Merlitz parameter of k=0.7, likewise discussed in the aforementioned publication, leads to a pincushion distortion of 5.3% to be used at the edge of the visual field for the specified visual field of +/−30°. This is observed by the embodiment of the further optical system 7 according to the invention under discussion here. Hence, the globe effect is avoided to the best possible extent.

[0258] In an even further embodiment of the further optical system 7 according to the invention, provision is made for a first beam to propagate from a first location on the display unit 5 in the light incidence direction L, for a second beam to propagate from a second location on the display unit 5 in the light incidence direction L, and for at least 70% or at least 80% or at least 90% of the first beam and the second beam to overlap at the intermediate pupil ZP. In other words, this embodiment of the further optical system 7 according to the invention provides for the first beam to propagate from the first location on the display unit 5 in the light incidence direction L, for the second beam to propagate from the second location on the display unit 5 in the light incidence direction L, and for the second lens group LG2 to be designed such that at least 70% or at least 80% or at least 90% of the first beam and the second beam overlap at the intermediate pupil ZP. The aforementioned embodiment ensures that the intermediate pupil ZP is imaged by the first lens group LG1 into the spatial region B (the eye box) without significant imaging aberrations, with the result that a one-to-one correspondence between the positions in the eye box B and the corresponding positions in the conjugate intermediate pupil ZP is maintained. All beams emanating from the various regions of the display unit 5 are uniformly vignetted by the aperture unit BE arranged in the plane of the intermediate pupil ZP. This ensures that the observer, when the pupil of their eye is laterally offset, perceives a reduction in the image brightness that occurs uniformly over the entire region of the display unit before, ultimately, there is complete trimming of the image.

[0259] The further optical system 7 according to the invention is advantageous in that it basically provides a conjugate equipment pupil. This allows the observer to directly and intuitively perceive their eye position departing from the admissible region of the eye box B. Further, the observer is provided with feedback regarding the direction and distance that they should move their eye laterally relative to the optical axis OA of the further optical system 7 according to the invention, in order to be sufficiently centered again with respect to the optical axis OA of the further optical system 7 according to the invention.

[0260] Individual or multiple features of the further optical system 7 can be implemented on at least one of the optical systems 7 described above.

[0261] The features of the invention disclosed in the present description, in the drawings and in the claims may be essential for the realization of the invention in the various embodiments thereof both individually and in arbitrary combinations. The invention is not restricted to the described embodiments. It can be varied within the scope of the claims and taking into account the knowledge of the relevant person skilled in the art.

LIST OF REFERENCE SIGNS

[0262] 1 Piece of night vision equipment [0263] 2 Eye [0264] 3 Objective [0265] 4 Detector [0266] 5 Display unit [0267] 6 Eyepiece [0268] 7 Optical system [0269] 8 Edge of the display unit [0270] 9 Marginal ray light beam [0271] B Spatial region (eye box) [0272] BE Aperture unit [0273] H1 First chief ray height [0274] H2 Second chief ray height [0275] HS Chief ray [0276] L Light incidence direction [0277] L1 First lens [0278] L2 Second lens [0279] L3 Third lens [0280] L4 Fourth lens [0281] L5 Fifth lens [0282] L6 Sixth lens [0283] L7 Seventh lens [0284] L8 Eighth lens [0285] L9 Ninth lens [0286] L10 Tenth lens [0287] L11 Eleventh lens [0288] L12 Twelfth lens [0289] L13 Thirteenth lens [0290] L14 Fourteenth lens [0291] LG1 First lens group [0292] LG2 Second lens group [0293] LG2′ Second lens group [0294] LG3′ Third lens group [0295] O Object [0296] OA Optical axis [0297] P1 First point [0298] P2 Second point [0299] P3 Third point [0300] P4 Fourth point [0301] S Sagittal contrast curves [0302] T Tangential contrast curves [0303] ZB Intermediate image [0304] ZP Intermediate pupil