CATADIOPTRIC EYEPIECE SYSTEM, EYEPIECE SYSTEM AND OPTICAL SYSTEM

Abstract

Catadioptric eyepiece system having an exit pupil, comprising a display having a surface disposed in an object plane; optics providing a beam path from the display to the exit pupil and being configured to image a portion of the object plane into an intermediate image formed in a curved intermediate image plane; wherein the optics comprise: a lens system of positive optical power comprising at least one lens, wherein the lens system is disposed in the beam path downstream of the display and upstream of the intermediate image; a concave first mirror disposed in the beam path downstream of the intermediate image and upstream of the exit pupil; and a first beam splitter disposed in the beam path between the lens system and the first mirror and between the first mirror and the exit pupil.

Claims

1. A catadioptric eyepiece system having an exit pupil, comprising: a display having a surface disposed in an object plane; optics providing a beam path from the display to the exit pupil and being configured to image a portion of the object plane into an intermediate image formed in a curved intermediate image plane; wherein the optics comprise: a lens system of positive optical power comprising at least one lens, wherein the lens system is disposed in the beam path downstream of the display and upstream of the intermediate image; a concave first mirror disposed in the beam path downstream of the intermediate image and upstream of the exit pupil; and a first beam splitter disposed in the beam path between the lens system and the first mirror and between the first mirror and the exit pupil.

2. The catadioptric eyepiece system according to claim 1, wherein a focal plane of the first mirror coincides with the curved intermediate image plane if the optics are set for an emmetropic eye.

3. The catadioptric eyepiece system according to claim 1, wherein the curved intermediate image plane has a radius of curvature less than 200 mm, in particular less than 80 mm, more in particular less than 20 mm.

4. The catadioptric eyepiece system according to claim 1, wherein the intermediate image is a real image.

5. The catadioptric eyepiece system according to claim 1, wherein the first mirror has a radius of curvature less than 180 mm, in particular less than 90 mm, more in particular less than 50 mm.

6. The catadioptric eyepiece system according to claim 1, wherein at least a portion of the intermediate image is formed within a first beam splitter element containing the first beam splitter.

7. The catadioptric eyepiece system according to claim 1, wherein at least one of the display and the at least one lens are displaceable relative to each other along an optical axis for diopter compensation.

8. The catadioptric eyepiece system according to claim 1, wherein the first mirror and the first beam splitter are configured to generate an eye relief being greater than 10 mm, in particular greater than 20 mm, more particular greater than 30 mm.

9. The catadioptric eyepiece system according to claim 1, wherein the first mirror is one of a front surface mirror, a back surface mirror and a mirror sharing a common surface with a first beam splitter element containing the first beam splitter, wherein the common surface is disposed in the beam path.

10. The catadioptric eyepiece system according to claim 1, wherein the first beam splitter is configured to direct rays of the beam path emerging from the intermediate image to the first mirror and to direct rays emerging from the first mirror to the exit pupil.

11. The catadioptric eyepiece system according to claim 1, wherein the lens system and the first mirror are configured to compensate for each other's Petzval curvature.

12. The catadioptric eyepiece system according to claim 11, wherein the lens system and the first mirror are configured so that an absolute value of a Petzval radius of curvature of the catadioptric eyepiece system is greater than 150 mm, in particular greater than 200 mm, more in particular greater than 250 mm.

13. The catadioptric eyepiece system according to claim 1, wherein the optics further comprise a second mirror disposed in the beam path downstream of the lens system and upstream of the intermediate image.

14. The catadioptric eyepiece system according to claim 13, wherein the optics further comprise a second beam splitter disposed in the beam path between the lens system and the second mirror.

15. The catadioptric eyepiece system according to claim 1, wherein the optics are further configured to form an intermediate pupil in the beam path upstream of the intermediate image.

16. The catadioptric eyepiece system according to claim 1, wherein the at least one lens comprises at least one of a cemented lens element, a lens having an aspheric surface and a meniscus lens, wherein at least one surface of the meniscus lens is concentric to a center of the intermediate pupil.

17. The catadioptric eyepiece system according to claim 1, wherein the optics are further configured to form the intermediate pupil outside of the lens system.

18. The catadioptric eyepiece system according to claim 1, further comprising: a light source configured to emit illumination light; a third beam splitter disposed in a beam path between the light source and the display, wherein the third beam splitter is configured to direct the illumination light onto the flat surface and to direct light reflected by the display into the beam path of the optics; wherein the display is a reflective display, in particular one of a liquid crystal on silicon display and a digital micromirror device.

19. The catadioptric eyepiece system according to claim 18, wherein a working distance between the object plane and a first surface of the optics is greater than 30 mm, in particular greater than 35 mm, more in particular greater than 40 mm.

20. The catadioptric eyepiece system according to claim 1, wherein the display is a light emitting display.

21. The catadioptric eyepiece system according to claim 1, wherein the exit pupil has a diameter being greater than 5 mm, in particular greater than 9 mm, more in particular greater than 14 mm.

22. The catadioptric eyepiece system according to claim 1, further comprising an aperture stop disposed in the beam path between the first beam splitter and the display.

23. The catadioptric eyepiece system according to claim 1, further comprising a polarizer disposed upstream of the first beam splitter and a waveplate disposed between the first beam splitter and the first mirror and wherein transmission and reflection of the first beam splitter are polarization dependent.

24. The catadioptric eyepiece system according to claim 1, wherein the first beam splitter is configured to direct infrared light emitted by an analysis apparatus for analyzing a patient's eye to the exit pupil.

25. An eyepiece system comprising at least two catadioptric eyepiece systems according to claim 1, wherein the first beam splitters of the at least two catadioptric eyepiece systems are portions of a single beam splitter.

26. The eyepiece system according to claim 25, wherein the lens system, the first mirror and the exit pupil of the at least two catadioptric eyepiece systems are displaceable relative to each other in a direction parallel to a long side of the single beam splitter.

27. The eyepiece system according to claim 25, wherein the first mirrors of the at least two catadioptric eyepiece systems are located on different sides of the single beam splitter.

28. An optical system having an eyepiece system according to claim 1, wherein the optical system comprises at least one of an optical microscope, a surgical microscope, a viewfinder, a charged particle beam microscope and a head-mounted display.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The forgoing as well as other advantageous features of the disclosure will be more apparent from the following detailed description of exemplary embodiments with reference to the accompanying drawings. It is noted that not all possible embodiments necessarily exhibit each and every, or any, of the advantages identified herein.

[0051] FIG. 1 shows a schematic illustration of an exemplary embodiment of a catadioptric eyepiece system;

[0052] FIG. 2 shows a schematic illustration of another exemplary embodiment of a catadioptric eyepiece system;

[0053] FIG. 3 shows a schematic illustration of another exemplary embodiment of a catadioptric eyepiece system;

[0054] FIG. 4 shows a schematic illustration of another exemplary embodiment of a catadioptric eyepiece system;

[0055] FIG. 5 shows a schematic illustration of another exemplary embodiment of a catadioptric eyepiece system; and

[0056] FIG. 6 shows a schematic illustration of an embodiment of an eyepiece system.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0057] In the exemplary embodiments described below, components that are alike in function and structure are designated as far as possible by alike reference numerals. Therefore, to understand the features of the individual components of a specific embodiment, the descriptions of other embodiments and of the summary of the disclosure should be referred to.

[0058] FIG. 1 shows an embodiment of a catadioptric eyepiece system 1. The catadioptric eyepiece system 1 comprises a display 3 having a flat surface 5. The display 3 is configured to generate the light image on the flat surface 5. The display 3, in particular the flat surface 5, is disposed in an object plane 7. In case of the embodiment shown in FIG. 1, the display 3 is a reflective display such as a liquid crystal on silicone display which, together with an illumination system 9, may generate bright images as compared to light emitting displays. The illumination system 9 comprises a light source 11 and a condenser lens 13 configured to direct illumination light 15 towards the display 3, in particular onto the flat surface 5. A third beam splitter 17 is disposed in a beam path between the illumination system 9, in particular the light source 11, and the display 3. The third beam splitter 17 is configured to direct the illumination light 15 onto the flat surface 5 of the display 3. In particular, according to the embodiment illustrated in FIG. 1, the third beam splitter 17 is configured to transmit the illumination light 15 to the flat surface 5.

[0059] The catadioptric eyepiece system 1 further comprises optics 19 providing a beam path 21 from the display 3 to an exit pupil 23 of the catadioptric eyepiece system 1. An infinite conjugate image of the image generated by the display 3 is formed by the optics 19. The exit pupil 23 disposed in an aperture plane 45 is given by the image of an aperture stop that may be disposed at an intermediate pupil 35, seen from the observer's side.

[0060] The optics 19 are configured to image a portion of the object plane 7 into an intermediate image 24 formed in a curved intermediate image plane 25. For this, the optics 19 comprise a lens system 27, wherein the lens system 27 provides a positive refractive power. In the embodiment illustrated in FIG. 1, the lens system 27 comprises five lenses L1, L2, L3, L4 and L5. The lens L4 is a doublet such as cemented lens element comprising lens elements L4-1 and L4-2. The lens system 27 may comprise spherical lenses, aspheric lenses, i.e. lenses having an aspheric surface, and/or a lens with a diffractive optical surface. The individual lenses L1, L2, L3, L4 and L5 may be selected as to reduce aberrations such as spherical aberration, astigmatism, etc. as well as color aberrations of the catadioptric eyepiece system.

[0061] The lens system 27 may be configured to provide a sufficiently large working distance in order to allow disposing the third beam splitter 17 in the beam path between the object plane 7 and a first surface 33 of the optics. The first surface is a surface, i.e. an optical interface between media having different refractive indices, which is first crossed by the beam path 21. Alternatively, the first surface may be regarded as a surface of the lens system 27 first crossed by the beam path 21. The optics 19, in particular the lens system 27, is configured to form an intermediate pupil 35 in the beam path 21 upstream of the intermediate image 24. The optics 19, in particular the lens system 27, is configured to image an aperture stop disposed at the intermediate pupil 35 to infinity when seen from the display's side. Thus, the system is telecentric, i. e. the principal rays at the display are parallel to the optical axis. Light rays emerging from the object plane 7 in a same direction, i.e. parallel rays emerging from the object plane 7, cross the intermediate pupil 35 at a same location but at different angles relative to the intermediate pupil 35. Furthermore, rays emerging from the object plane 7 into different directions but from a same point on the object plane 7 cross the intermediate pupil 35 at different locations within the intermediate pupil 35. In the embodiment illustrated in FIG. 1, the intermediate pupil 35 is located outside of the lens system 27 and, in particular, outside of one of the lenses L1, L2, L3, L4 and L5 of the lens system 27.

[0062] Note that a portion of the intermediate image 24 is formed within the first beam splitter element 41.

[0063] The optics 19 further comprise a concave first mirror 37 which is a front surface mirror and a first beam splitter 39. The first mirror 37 is disposed in the beam path 21 downstream of the intermediate image 24 and upstream of the exit pupil 23. In particular, the first mirror 37 may be a spherical mirror. Note that some of the rays illustrated in FIG. 1 run above and below the paper plane of FIG. 1. These rays are projected onto the paper plane, which is the reason why not all of the illustrated rays are drawn up to a surface 38 of the mirror 37.

[0064] The first beam splitter 39 is disposed in the beam path 21 disposed in the beam path 21 between the lens system 27 and the first mirror 37 and between the first mirror 37 and the exit pupil 23. In particular, the beam splitter 39 is disposed in the beam path 21 between the intermediate image 24 and the first mirror 37.

[0065] The optics may comprise displaceable elements, for example the display 3. This embodiment is well suited for compensation of ametropia of the observer by moving display 3 along the optical axis for the following reason. Since the eyepiece is telecentric at display's side, the principal rays are parallel to the optical axis. Therefore, by shifting the display 3 along an optical axis ametropia of observer's eye can be corrected for whereas the magnification does not change. Especially when two eyepieces are used for two eyes of the observer, a constant magnification ensures that both images appear under the same magnification which mitigates unwanted effects such as binocular rivalry. Alternatively, also the lenses L1 and/or L2 and/or L3 and/or L4 and/or L5 of the lens system 27 and/or the display 3 may be displaceable relative to each other in order to allow for a diopter compensation, i.e. a compensation for an ametropia of an observer's eye. When the optics 19, in particular the display 3 and the lens system 27, are set for an emmetropic eye, the first mirror 37 and the beam splitter 39 as well as a first beam splitter element 41 containing the first beam splitter 39 are configured to generate an infinite conjugate image of the intermediate image 24 which can be observed by an observer's eye when the pupil of the eye intersects the exit pupil 23.

[0066] As the lens system 27 provides a positive optical power, the lens system 27 has a positive Petzval curvature. Similarly, the concave first mirror 37 provides a positive optical power, however this results in a negative Petzval curvature. Therefore, by appropriately selecting the optical properties of the lens system 27 and the concave first mirror 37, the Petzval curvatures may compensate each other so that an essentially vanishing Petzval curvature is achieved for the beam path 21.

[0067] As described above, the catadioptric eyepiece system 1 provides a diopter compensation by providing displaceable components of the optics 19. FIG. 1 shows the catadioptric eyepiece system 1 wherein the optics 19 are set for an emmetropic eye. Therefore, a focal plane of the first mirror 37 coincides with the curved intermediate image plane 25 so that the first mirror 37 generates an infinite conjugate image of the intermediate image 24 which can be observed by an observer's eye intersecting the exit pupil 23.

[0068] The first mirror 37 and the first beam splitter 39, and in particular the first beam splitter element 41, are configured to generate a convenient eye relief. The eye relief is the distance between the exit pupil 23 and a last surface 43 of the optics 19 crossed by the beam path 21. In particular, the eye relief is the distance between the exit pupil 23 and the last surface 43 of the first beam splitter element 41 crossed by the beam path 21. The eye relief is indicated by a distance d and convenient values of the eye relief may amount to values greater than 12 mm.

[0069] Another aspect of the catadioptric eyepiece system 1 is the available field of view FOV. The field of view may be represented by an angle of view θ between the optical axis 44 and an oblique ray 46 transmitted through the eyepiece system 1. By appropriately selecting the focal length of the optics 19 and the size of the display 3, the angle θ may amount to a value of at least 20° in a horizontal plane and at least 15° in a vertical plane.

[0070] Detailed information on parameters of lenses and mirrors, such as the type and optical power of the lenses and the radius of curvature of the mirror are listed in Table 1.

TABLE-US-00001 TABLE 1 # Type Optical Power (diopter) L1 Glas Sumita KGFK68 +12.700 L2 Glas Ohara SFPL53 +13.690 L3 Glas Schott NBK7 +15.362 L4-1 Glas Ohara SFPL53 +11.697 L4-2 Glas Schott NKZFS8 −29.558 L5 Gas Schott NBK7 +24.811 Radius of Curvature (mm) 41 Schott SF10 — 37 — 67

[0071] FIG. 2 shows a schematic illustration of another exemplary embodiment of a catadioptric eyepiece system 1A which is similar to the system 1 illustrated in FIG. 1. In contrast to the system 1 illustrated in FIG. 1, the lens system 27A of the catadioptric eyepiece system 1A illustrated in FIG. 2 comprises four lenses L1A, L2A, L3A and L4A, wherein L3A is a doublet of the lens elements L3A-1 and L3A-2.

[0072] In contrast to the system 1 of FIG. 1, the display 3A is configured to emit light actively. As an example, the display 3A could be a transmissive LCD display which is illuminated from the back side by parallel bundles of light which enclose a certain maximum angle with the normal to the flat surface 5A. As a consequence, each pixel of the display emits a cone of light with a given numerical aperture NA and with an axis being perpendicular to the flat surface 5A of the display 3A Thus, the principal rays which are similar to the axes of the light cones perpendicular to the flat surface 5A. The system 1A illustrated in FIG. 2 also forms an intermediate pupil 35A where the principal rays converge. However the intermediate pupil 35A is not accessible as it is located within the lens L4A.

[0073] Detailed information on parameters of the lenses are listed in Table 2 wherein the radii and center-thicknesses are given in units of mm. “DIST” denotes a distance in mm between respective lenses. Surfaces of the lenses are enumerated in the order the beam path passes them from the display 3A to the exit pupil 23A.

[0074] The distance between the first beam splitter element 41A and L4A amounts to 21 mm.

[0075] The edge length of the first beam splitter element 41A amounts to 48 mm and it consists of SF10. The first mirror 37A is disposed at a distance of 13 mm from the first beam splitter element 41A.

TABLE-US-00002 TABLE 2 Center- Optical Power Radius Thickness # Type (diopter) Surface [mm] [mm] L1A NLASF41 17.7 1 ∞ 7 2 47.438 DIST 0.1 L2A SPHM52 18.0 3 34.479 8.2 4 ∞ DIST 0.1 L3A-1 NSK5 22.1 5 23.447 11.4 6 58.504 L3A-2 NSF6 −39.5 7 58.504 3 8 13.914 DIST 2.8 L4A STIM5 34.0 9 23.673 16 10  54.596

[0076] In contrast to the embodiment illustrated in FIG. 1, the catadioptric eyepiece system 1A further comprises a polarizer 81A and a waveplate 83A and the reflection and transmission of the first beam splitter element 41A are polarization dependent. In particular, the polarizer 81A is disposed between the first beam splitter element 41A and the lens system 27A and is configured to transmit light polarized in a first direction only. However, the polarizer may be included in the third beam splitter 17A, for example. The waveplate is a quarter-wave plate disposed between the first beam splitter element 41A and the first mirror 37A and is configured to convert linearly polarized light into circularly polarized light and vice versa. The first beam splitter element 41A is a MacNeille beam splitting cube or a wire grid beamsplitter.

[0077] For example, the first beam splitter 39A provided by the first beam splitter element 41A may configured to reflect almost 100% of light polarized in the first direction and to transmit almost 100% of light polarized in a second direction orthogonal to the first direction.

[0078] As a consequence, light entering the first beam splitter element 41A from the polarizer 81A is linearly polarized in the first direction and almost 100% of this light is reflected at the first beam splitter 39A towards the first mirror 37A. Subsequently, the light linearly polarized in the first direction is converted into circularly polarized light by the waveplate 83A. Upon reflection at the first mirror 37A, the handiness of the circularly polarized light is inverted. Subsequently, the circularly polarized light having the inverted handiness is converted into light linearly polarized in the second direction by the waveplate 83A. As the first direction is orthogonal to the second direction, the first beam splitter element can transmit almost 100% of the light being linearly in the second direction coming from the first mirror 37A.

[0079] As a consequence, downstream of the polarizer 81A, nearly no light is reflected into the upstream direction which, in turn, reduces stray light and enhances the contrast at the exit pupil.

[0080] Assuming that unpolarized light is incident onto the polarizer 81A, about 50% of the unpolarized light is lost for the imaging due to the polarizer 81A. However, as nearly no light is lost downstream of the polarizer 81A, a total of 50% of the light incident onto the polarizer 81A can be received at the exit pupil. In contrast to that, without providing the polarizer, waveplate and polarization dependent properties of the first beam splitter and assuming a 50/50-beam splitter as the first beam splitter, only 25% of the light entering the first beam splitter element from the lens system can be provided at the exit pupil.

[0081] In case a transmissive LCD display is used in combination with FIG. 2, the polarizer 81A could be omitted since the light transmitted by the LCD display in the direction of the eyepiece optics is already linearly polarized.

[0082] In case an LCoS display is used in combination with FIG. 2, the third beamsplitter 17A may be a polarization beam splitter. In this case, the polarizer 81A could be omitted since the light reflected at the beamsplitter 17A is already linearly polarized.

[0083] Although only the embodiment illustrated in FIG. 2 is equipped with the polarizer, waveplate and polarization dependent first beam splitter in the description, the concept may be employed in the other embodiments described herein without additional effort.

[0084] FIG. 3 shows a schematic illustration of another exemplary embodiment of a catadioptric eyepiece system 1B. Similarly to the embodiment illustrated in FIG. 1, the catadioptric eyepiece system 1B illustrated in FIG. 3 also comprises a display 3B having a flat surface 5B disposed in an object plane 7B. The catadioptric eyepiece system 1B further comprises optics 19B comprising a lens system 27B, a concave first mirror 37B and a first beam splitter 39B. The lens system 27B comprises four lenses L1B, L2B, L3B and L4B. Furthermore, the catadioptric eyepiece system 1B has an exit pupil 23B.

[0085] The optics 19B are configured to image a portion of the object plane 7B into an intermediate image 24B formed in a curved intermediate image plane 25B.

[0086] In contrast to the reflective display 3 of the embodiment illustrated in FIG. 1, the catadioptric eyepiece system 1B has a light emitting display. The light emitting display 3B may be configured to generate an image on the flat surface 5B by actively emitting light. Four exemplary rays 47B, 49B, 51B and 53B emerge from the display 3B into a beam path 21B from the display 3B to the exit pupil 23B. The rays are first incident onto a first surface 33B of the first system 27B. Note that some of the rays illustrated in FIG. 3 run above and below the paper plane of FIG. 3.

[0087] The optics 19B, in particular the lens system 27B, is configured to generate an intermediate pupil 35B upstream of the intermediate image 24B. Rays 47B and 51B parallely emerging from the object plane 7B pass the intermediate pupil 35B at a same location 52B.

[0088] Note that the lens system 27B is configured to generate the intermediate pupil 35B within the lens system 27B, in particular within the lens L4B of the lens system 27B.

[0089] Furthermore, the lens system 27B comprises a meniscus lens 55B as L3B, i. e. curvatures of two surfaces 57B of the meniscus lens 55B opposite to each other have the same sign which means that the curvature of said surfaces are directed into a same direction. In particular, the surfaces 57B of the meniscus lens 55B may be concentric to a center 59B of the intermediate pupil 35B, i. e. a point located at the intersection of an optical axis 61B of the optics 19B, in particular the lens system 27B, and the intermediate pupil 35B. That is, at least a portion of each of the surfaces 57B coincides with a surface of a virtual sphere centered at the center 59B of the intermediate pupil 35B, wherein the radius of the virtual sphere corresponds to the radii of curvature of the surfaces 57B, respectively. Simultaneously, the center 59B may be an intermediate pupil for the first mirror 37B. In this case, the meniscus lens 55B can compensate spherical aberrations of all field bundles generated by the first mirror 37B.

[0090] The first beam splitter 39B contained in a first beam splitter element 41B is configured to transmit the beam path 21B emerging from the lens system 27B to the first mirror 37B and to reflect light emerging from the first mirror 37B to the exit pupil 23B. The first mirror 37B is a front surface mirror. As the lens system 27B has positive optical power resulting in a positive Petzval curvature and the first mirror 37B, the first beam splitter 39B and the first beam splitter element 41B together have a positive optical power resulting in a negative Petzval curvature, the Petzval curvatures may compensate each other. Therefore, the Petzval curvature of the optics 19B may be reduced resulting in high quality imaging.

[0091] The catadioptric eyepiece system 1B may be configured to provide a diopter compensation by providing displaceable components of the optics 19B. In particular, the display 3B and at least one lens of the lens system 27B may be displaceable relative to each other in order to provide the diopter compensation. When the catadioptric eyepiece system 1B is set for an emmetropic eye, an infinite conjugate image of the image generated by the display 3B is formed at the exit pupil 23B, i. e. rays emerging from a same location of the object plane 7B are parallel to each other at the exit pupil 23B and rays emerging from the object plane 7B at different locations but at same inclinations relative to the object plane 7B are located at a same location in the exit pupil 23B. In particular, the rays 47B and 51B parallely emerging from the object plane 7B pass the exit pupil 23B at a same location 60B. The rays 47B and 49B emerging at different inclinations relative to the object plane 7B from a same location on the object plane 7B are parallel to each other at the exit pupil 23B.

[0092] FIG. 4 shows a schematic illustration of another catadioptric eyepiece system 1C. The catadioptric eyepiece system 1C comprises a display 3C having a flat surface 5C. The flat surface is disposed in an object plane 7C. The catadioptric eyepiece system has an exit pupil 23C and comprises optics 19C providing a beam path 21C from the display 3C to the exit pupil 23C. The optics 19C, in particular a lens system 27C comprising a lens L1C together with a second mirror 67C, are configured to image a portion of the object plane 7C into an intermediate image 24C formed in a curved intermediate image plane 25C. The second mirror 63C is a back surface mirror. Therefore, the second mirror 63C comprises a refractive element 69C and a reflective surface 67C attached to a surface of the refractive element 69C opposite to a second beam splitter 65C. The back surface mirror 63C and a second beam splitter element containing the second beam splitter 65C may provide additional degrees of freedom which may be used to compensate for various aberrations. As the portion of the optics upstream of the intermediate image 24C is catadioptric system itself, the configuration of this portion may be compact, i. e. its size may be small, in particular compared to the configuration of the catadioptric eyepiece systems 1, 1B. Also, a mirror does not introduce color aberrations which additionally simplifies the optical layout.

[0093] Note that the intermediate image 24C is formed upstream of a first beam splitter element 41C containing a first beam splitter 39C.

[0094] The configuration of a first mirror 37C, the first beam splitter 39C and the first beam splitter element 41C is similar to the configuration of said components of the catadioptric eyepiece system 1. A detailed description thereof is omitted and reference is made to the description of the embodiment illustrated in FIG. 1.

[0095] The catadioptric eyepiece system 1C may also provide a diopter compensation. For example, a diopter compensation may be provided by the lens system 27C, i. e. the lens L1C of the lens system 27C, or the second mirror 63C or the display 3C being displaceable relative to each other. FIG. 4 illustrates the catadioptric eyepiece system 1C set for an emmetropic eye. Therefore, rays emerging from the object plane 7C from different locations but at same inclinations relative to the object plane 7C, e. g. rays 47C and 51C, are located in a same location 60C at the exit pupil 23C. Furthermore rays emerging from a same point of the object plane 7C but at different inclinations relative to the object plane 7C, e. g. rays 47C and 49C, are parallel to each other at the exit pupil 23C at a distance from one another. That is, an infinite conjugate image of a portion of the object plane 7C is formed at the exit pupil 23C as the optics are set for an emmetropic eye.

[0096] Note that the portion of the optics upstream of the intermediate image 24C, i. e. the lens system 27C, the second mirror 63C and the second beam splitter 65C together provide a positive optical power resulting in a positive Petzval curvature. As before, the first mirror 37C and the first beam splitter 39C together with the first beam splitter element 41C provide a positive optical power but a negative Petzval curvature. Therefore, the Petzval curvatures may compensate each other. In particular, the optical properties of said components may be selected so that the Petzval curvatures cancel each other effectively.

[0097] Detailed information on parameters of lenses and mirrors, such as thickness of the lens, material, radius of curvature as well as distances are listed in Table 3 (in units of ram).

TABLE-US-00003 TABLE 3 # Thickness/Distance Radius Material 7C — — L1C 5.2 29.728 Air 5.0 −23.028 SK5 69C 23.0 134.135 Air 63C 2.5 −55.666 Mirror 69C −2.5 134.135 SK5 65C −12.0 — Mirror 12.0 — Air 41C 0.1 — Air 39C 25.0 — Mirror −25.0 — SF6 −0.1 — Air 37C −5.0 95.040 Mirror 5.0 — SK5 41C 0.1 — Air 41C 50.0 — SF6 45C 28.0 — Air

[0098] The first mirror 37C may be aspherical and be described by the aspheric constants C1=3.0850890.10.sup.−7 mm.sup.−3 and C2=4.844320840.sup.−11 mm.sup.−5. The second mirror 63C, in particular its surface 67C, may be aspherical and be described by the aspheric constants C1=−2.7433401.10.sup.−6 mm.sup.−3 and C2=4.2089045.10.sup.−10 mm.sup.−5. The surface of lens L1C facing the second mirror 63C may be aspherical and be described by the aspheric constants C1=−4.660597.10.sup.−5 mm.sup.−3 and C2=−3.92890929.10.sup.−8 mm.sup.−5.

[0099] FIG. 5 shows a schematic illustration of another eyepiece system 1D. The eyepiece system 1D may be a portion of the eyepiece systems illustrated in FIGS. 1 to 4. The eyepiece system 1D comprises a lens system 27D, a first beam splitter 39D embodied by a first beam splitter element 41D and a first mirror 37D which may function as their counterparts described above.

[0100] In contrast to the embodiments of the eyepiece systems described with reference to FIGS. 1 to 4, the first beam splitter 39D is configured to direct infrared light, i e. light of wavelengths being greater than 750 nm, to an exit pupil 23D. Further an analysis apparatus 90D for analyzing a patient's eye may be provided and disposed so that (infrared) light emitted by the analysis apparatus 90D can be directed to the exit pupil 23D. The first beam splitter 39D may be configured to direct at least 80%, in particular more than 90% or more than 99%, of infrared light emitted by the analysis apparatus 90D to the exit pupil 23D.

[0101] In particular, as illustrated in FIG. 5, with respect to the first beam splitter 39D, the analysis apparatus 90D is disposed opposite to the lens system 27D, whereas the first mirror 37D is disposed opposite to the exit pupil 23D. The first beam splitter 39D is configured to reflect nearly all infrared light emitted by the analysis apparatus 90D and, hence, does not transmit infrared light. Accordingly, infrared light emitted by the analysis apparatus 90D does not enter the lens system but is fully directed towards the exit pupil 23D. Accordingly, the first beam splitter 39D may have a reflectance of at least 70%, in particular at least 90% or at least 99%, for infrared light.

[0102] Alternatively, the analysis apparatus 90D and the first mirror 37D may be interchanged in position and the first beam splitter 39D may be configured to transmit infrared light and to not reflect infrared light. Thus, again, nearly all infrared light emitted by the analysis apparatus 90D is directed to the exit pupil 23D. Accordingly, the first beam splitter may have a transmittance of at least 70%, in particular at least 90% or at least 99%, for infrared light.

[0103] Consequently, while providing the function of the eyepiece system as described above, the patient's eye may be analyzed by the analysis apparatus 90D using infrared light without interfering with the function of the eyepiece system. The analysis apparatus may comprise different monitoring systems to monitor the eye of the observer, e. g. a gaze tracker or an objective accommodation measurement device which measures the accommodation of observer's eye.

[0104] Alternatively to the embodiment described with reference to FIG. 5, a beam splitter different from the first beam splitter may be disposed in the beam path provided by the eyepiece system for introducing infrared light of an analysis apparatus into the beam path and to direct the infrared light towards a patient's eye. For example, the additional beam splitter may be disposed in the beam path between the first beam splitter and the exit pupil.

[0105] FIG. 6 shows a schematic illustration of an eyepiece system 100. The eyepiece system 100 comprises two catadioptric eyepiece systems 101 and 102. In particular, each of the catadioptric eyepiece systems 101 and 102 is one of the catadioptric eyepiece systems described above. The catadioptric eyepiece system 101 comprises a portion 103 upstream of its first beam splitter 105, its first beam splitter 105 and its concave first mirror 107. Similarly, the catadioptric eyepiece system 102 comprises a portion 104 of optics upstream of its first beam splitter 109, its first beam splitter 109 and its concave first mirror 111. Both the first beam splitter 105 of the catadioptric eyepiece system 101 and the first beam splitter 109 of the catadioptric eyepiece system 102 are portions of a single beam splitter 113.

[0106] In the eyepiece system 100, the catadioptric eyepiece system 102 is displaceable relative to the catadioptric eyepiece system 101 as indicated by arrows 115. In particular, the portions 103 and 104 each comprising a lens system, the first mirror 107 and 111 and exit pupils of the catadioptric eyepiece systems 101 and 102 may be displaceable relative to each other in a direction parallel to a long side of the single beam splitter 113. Therefore, the eyepiece 100 may be adapted to an interpupilar distance 117 between an observer's eyes 119. The first mirrors 111 and 115 are disposed on different sides of the singe beam splitter 113. Therefore, the first mirrors do not obstruct each other when displaced along the long side.

[0107] While the disclosure has been described with respect to certain exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the disclosure set forth herein are intended to be illustrative and not limiting in any way. Various changes may be made without departing from the spirit and scope of the present disclosure as defined in the following claims.