Lens with a Fixed Focal Length and a Constant Structural Length for Autofocus Applications

Abstract

A lens with a fixed focal length comprising including a first front lens-element group, a second lens-element group, a third lens-element group, a fourth lens-element group, and a fifth back lens-element group. Relative to an imaging plane in a lens barrel and both the focusing front group and the focusing back group are movable jointly relative to one another and to the lens-element groups arranged in a stationary manner in order to focus the lens on objects at different object distances. The front lens-element group has a positive refractive power and the central group and the back lens-element group have a negative refractive power.

Claims

1. A lens with a fixed focal length, comprising: five lens-element groups, wherein three lenses are mounted in a stationary manner and two lenses are mounted in a displaceable manner along an optical axis, wherein a first front lens-element group as viewed from an object side is arranged in a stationary manner, a second lens-element group configured as a focusing front group is arranged in a displaceable manner, a third lens-element group containing a stationary iris diaphragm, the aperture of which is adjustable, configured as a central group is arranged in a stationary manner, a fourth lens-element group configured as a focusing back group is arranged in a displaceable manner, and a fifth back lens-element group is arranged in a stationary manner relative to an imaging plane in a lens barrel and both the focusing front group and the focusing back group are movable jointly relative to one another and to the lens-element groups arranged in a stationary manner in order to focus the lens on objects at different object distances, and the front lens-element group has a positive refractive power and the central group and the back lens-element group have a negative refractive power.

2. The lens as claimed in claim 1, wherein the focusing front group and the focusing back group have a positive refractive power.

3. The lens as claimed in claim 2, wherein both the focusing front group and the focusing back group move away from the imaging plane during focusing from infinity to the near setting.

4. The lens as claimed in claim 3, wherein the ratio f1/f of the focal lengths f1 of the front lens-element group and f of the entire lens lies between 0.5 and 30, the ratio f2/f of the focal lengths f2 of the focusing front group and f of the entire lens lies between 0.3 and 10, the ratio f3/f of the focal lengths f3 of the central group and f of the entire lens lies between 30 and 0.3, the ratio f4/f of the focal lengths f4 of the focusing back group and f of the entire lens lies between 0.1 and 10, and the ratio f5/f of the focal lengths f5 of the back lens-element group and f of the entire lens lies between 40 and 0.1.

5. The lens as claimed in claim 4, wherein the lens has a ratio of the total focal length f to the image circle diameter in the imaging plane of between 1 and 5.

6. The lens as claimed in claim 5, wherein the ratio V of the volume of the respective focusing elements to the image circle diameter in the imaging plane raised to the third power lies below 0.1 (V/Bd3<0.1), in particular below 0.08, or the weight of the respective focusing group lies below 15 g.

7. The lens as claimed in claim 6, wherein the front lens-element group consists of four lens elements wherein the first lens element has a positive refractive power, the second lens element has a positive refractive power, the third lens element has a positive refractive power and the fourth lens element has a negative refractive power, wherein the third lens element and the fourth lens element are combined to form a lens-element doublet having a negative total refractive power, or the front lens-element group consists of four lens elements, wherein the first lens element has a positive refractive power, the second lens element has a negative refractive power, the third lens element has a positive refractive power and the fourth lens element has a negative refractive power, wherein the third lens element and the fourth lens element are combined to form a lens-element doublet having a positive total refractive power, or the front lens-element group consists of three lens elements, wherein the first lens element has a positive refractive power, the second lens element has a positive refractive power and the third lens element has a negative refractive power, wherein the second lens element and the third lens element are combined to form a lens-element doublet having a negative or positive total refractive power.

8. The lens as claimed in claim 7, wherein either the central group consists of two lens elements and the iris diaphragm, wherein the first lens element has a negative refractive power and the second lens element has a positive refractive power, and the iris diaphragm is arranged in a stationary manner between the two of them, or the central group consists of five lens elements and the iris diaphragm, wherein the first lens element has a negative refractive power, the second lens element has a negative refractive power, the third lens element has a positive refractive power, the fourth lens element has a negative refractive power and the fifth lens element has a positive refractive power, wherein the fourth lens element and the fifth lens element are combined to form a lens-element doublet having a positive total refractive power and the iris diaphragm is arranged in a stationary manner between the first lens element and the second lens element.

9. The lens as claimed in claim 8, wherein either the back lens-element group consists of three lens elements, wherein the first lens element has a positive refractive power, the second lens element has a negative refractive power and the third lens element has a negative refractive power, wherein the first lens element and the second lens element are combined to form a lens-element doublet having a positive total refractive power, or the back lens-element group consists of three lens elements, wherein the first lens element has a negative refractive power, the second lens element has a positive refractive power and the third lens element has a negative refractive power.

10. The lens as claimed in claim 9, wherein at least one of the five lens-element groups contains a lens element having one or two aspherical surfaces, preferably the stationary lens-element group.

11. The lens as claimed in claim 10, wherein the back lens-element group contains at least one lens element comprising an optical material having a refractive index ne of greater than 1.8.

12. The lens as claimed in claim 11, wherein the central group contains at least one lens element comprising an optical material having anomalous partial dispersion SCD of less than 0.07 or greater than 0.07.

13. The lens as claimed in claim 12, wherein the front lens-element group contains at least one lens element comprising an optical material having anomalous partial dispersion SCD of greater than 0.07.

14. The lens as claimed in claim 13, wherein at least one of the focusing groups contains a lens element comprising an optical material having anomalous partial dispersion SCD of greater than 0.07.

Description

[0041] In this case, in the figures:

[0042] FIG. 1 shows a lens-element section through a lens with the focal length 75 mm,

[0043] FIG. 2 shows a lens-element section through a lens with the focal length 90 mm,

[0044] FIG. 3 shows a lens-element section through a lens with the focal length 75 mm,

[0045] FIG. 4 likewise shows a lens-element section through a lens with the focal length 75 mm, and

[0046] FIG. 5 shows the lens-element section through a further lens with the focal length 75 mm,

[0047] FIG. 6 shows an image sensor in an imaging plane IM.

[0048] The movement paths of the respective lens-element groups during the focusing process are illustrated below the lens-element sections in the figures. Horizontal lines represent the positions of the lens-element groups G1, G2, G3, G4 and G5. The upper lines thereof identify the positions in the focus setting infinity, the lower lines the positions in the focus setting at the shortest object distance, and the central lines the positions in a central focus setting. The perpendicular lines are assigned to the stationary lens-element groups G1, G3 and G5, and the oblique lines to the displaceable focusing groups G2 and G4.

[0049] The lens-element sections of FIGS. 1 to 4 apply for maximum aperture 2, while FIG. 5 shows a lens with the maximum aperture 1.4.

[0050] In the case of the lens illustrated in FIG. 1, the first lens-element group G1 having a positive total refractive power comprises in the light direction a convexo-concave lens element G1L1 having a positive refractive power, a convexo-concave lens element G1L2 having a positive refractive power and a lens-element doublet G1L3/G1L4 having a negative total refractive power, consisting of a biconvex lens element G1L3 having a positive refractive power and a biconcave lens element G1L4 having a negative refractive power. This lens-element group, referred to as front lens-element group, is stationary. The first lens-element surface of the lens-element doublet G1L3/G1L4 in the light direction is embodied aspherically.

[0051] A second and a fourth lens-element group G2 and G4 have a positive refractive power and are displaced simultaneously for focusing along the lines indicated underneath. Both focusing elements are embodied as single lens elements.

[0052] Arranged between the focusing elements is a stationary lens-element group G3 having a negative total refractive power, which consists of a first convexo-concave lens element G3L1 having a negative refractive power and a second concavo-convex lens element G3L2 having a positive refractive power. This central group is stationary and encloses an aperture stop (iris diaphragm) AP.

[0053] The back lens-element group G5, which is likewise stationary, has overall a negative refractive power and consists of a first biconvex lens element G5L1 having a positive refractive power and a second biconcave lens element G5L2 having a negative refractive power, which are joined together as a cemented element having overall a positive refractive power, and a third concavo-convex lens element G1L3 having a negative refractive power.

[0054] The lens-element section illustrated in FIG. 2 deviates from the lens-element section described with regard to FIG. 1 merely in the back lens-element group G5, wherein the lens elements G5L1, G5L2 and G5L3 are embodied as single lenses having the refractive power sequence (), (+), (). Moreover, three of the lens-element surfaces are embodied as aspherical surfaces.

[0055] The lens-element section illustrated in FIG. 3 deviates from the lens-element section described with regard to FIG. 1 merely in the front lens-element group G1 by virtue of the fact that the lens element G1L2 is realized as a convexo-concave lens element having a negative refractive power and having an aspherical front surface and the cemented element G1L3/G1L4 has overall a positive refractive power.

[0056] The lens-element section illustrated in FIG. 4 deviates from the lens-element section described with regard to FIG. 1 in the configuration of the front lens-element group G1, which here consists of only two lens elements, a first convexo-concave lens element G1L1 having a positive refractive power and a lens-element doublet G1L2/G1L3 having a negative total refractive power, consisting of a biconvex lens element G1L2 having a positive refractive power and a biconcave lens element G1L3 having a negative refractive power. In addition, the back lens-element group G5 is composed of three single lens elements G5L1, G5L2 and G5L3 having the refractive power sequence as illustrated with regard to FIG. 2. Moreover, a plurality of surfaces are embodied aspherically.

[0057] In the case of the lens-element section illustrated in FIG. 5, the front lens-element group consists of two lens elements, wherein the second lens element is embodied as a cemented element G1L2/G1L3 having overall a positive refractive power. The central group G3 consists of a first convexo-concave lens element G3L1 having a negative refractive power upstream of the aperture stop (iris diaphragm) AP, a second biconcave lens element G3L2 having a negative refractive power downstream of the aperture stop (iris diaphragm) AP, a biconvex lens element having a positive refractive power G3L3 and a fourth lens element G3L4/G3L5 embodied as a cemented element and having overall a positive refractive power. The back lens-element group G5 consists of two lens elements, of which the first is embodied as a lens-element doublet (cemented element) having a biconvex lens element G5L1 having a positive refractive power and a biconcave lens element G5L2 having a negative refractive power, and a thin convexo-concave lens element having a negative refractive power. The convex lens-element surface is embodied aspherically.

[0058] The imaging is carried out in each case onto an image plane IM.

[0059] In the case of the circular imaging plane IM illustrated schematically in FIG. 6, a double-headed arrow represents an image circle diameter Bd, which corresponds to the diameter of an image sensor Bs illustrated in a rectangular fashion.

[0060] For all figures of the drawing relating to lens-element sections, the lens-element surfaces identified by an * are embodied aspherically.

[0061] The lens-element sections in the drawing are illustrated to scale, such that relative indications, such as e.g. the material thickness in the case of the lens element G3L1 in FIG. 1, which is considerably thinner in the lens-element center in comparison with the material thickness at the lens-element edge, can be diagrammatically established and checked using conventional geometric means. What is likewise disclosed in this way is that in FIG. 1 the lens element G3L2 has in the lens-element center a material thickness almost exactly four times (4.25 times) thicker than the lens element G2. These relationships are readily apparent to the person skilled in the art.

[0062] In all lens variants, the five lens-element groups described and illustrated individually represent a specifically necessary, self-contained constituent. Each of the lens-element groups can be optically tuned by itself, which is expressed in particular by the ratio of focal length specified for each lens-element group to the total focal length.

[0063] Concrete exemplary embodiments are evident from the tables below for lenses with 75 mm and 90 mm with a maximum aperture number of 2 and 1.4, wherein the focal lengths are in each case relative to the full-frame format (43.3 mm image circle diameter).

TABLE-US-00001 FIG. 1 1:2 75 Refractive Abbe Refractive mm index ne number ve SCD power [dpt.] G1 G1L1 1.85504 23.59 0.153 15.1 G1L2 1.49845 81.15 0.240 3.0 G1L3 1.62033 63.02 0.082 16.5 G1L4 1.81264 25.22 0.131 G2 1.49845 81.15 0.240 12.3 G3 G3L1 1.59911 38.97 0.019 12.0 G3L2 1.88815 40.52 0.107 1.1 G4 1.62033 63.02 0.082 12.6 G5 G5L1 1.88815 40.52 0.107 7.9 G5L2 1.60718 37.76 0.012 G5L3 1.58482 40.47 0.019 13.3

TABLE-US-00002 FIG. 2 1:2 75 Refractive Abbe Refractive mm index ne number ve SCD power [dpt.] G1 G1L1 1.85504 23.59 0.153 10.1 G1L2 1.49845 81.15 0.240 9.2 G1L3 1.49845 81.15 0.240 18.5 G1L4 1.74617 28.07 0.075 G2 1.49845 81.15 0.240 10.9 G3 G3L1 1.72538 34.47 0.089 13.2 G3L2 1.51872 63.96 0.012 2.2 G4 1.60520 65.16 0.072 16.8 G5 G5L1 1.65803 39.46 0.119 12.6 G5L2 1.85500 23.69 0.172 14.4 G5L3 1.62409 36 0.001 17.0

TABLE-US-00003 FIG. 3 1:2 75 Refractive Abbe Refractive mm index ne number ve SCD power [dpt.] G1 G1L1 1.85649 32.03 0.005 17.1 G1L2 1.55098 45.49 0.007 16.9 G1L3 1.62033 63.02 0.082 1.6 G1L4 1.67765 31.85 0.042 G2 1.49845 81.15 0.240 14.3 G3 G3L1 1.67765 31.85 0.042 13.1 G3L2 1.60520 65.16 0.072 2.6 G4 1.88815 40.52 0.107 14.4 G5 G5L1 1.88815 40.52 0.107 6.0 G5L2 1.61664 44.27 0.147 G5L3 1.65222 33.53 0.022 13.4

TABLE-US-00004 FIG. 4 1:2 75 Refractive Abbe Refractive mm index ne number ve SCD power [dpt.] G1 G1L1 1.81643 22.57 0.286 14.5 G1L2 1.43985 94.49 0.327 15.0 G1L3 1.74617 28.07 0.075 G2 1.43985 94.49 0.327 12.1 G3 G3L1 1.81643 22.57 0.286 18.3 G3L2 1.60520 65.16 0.072 11.7 G4 1.60520 65.16 0.072 14.4 G5 G5L1 1.65803 39.46 0.119 11.1 G5L2 1.97188 17.33 0.755 12.1 G5L3 1.62408 36.16 0.002 18.1

TABLE-US-00005 FIG. 5 1:1.4 75 Refractive Abbe Refractive mm index ne number ve SCD power [dpt.] G1 G1L1 1.85504 23.59 0.153 9.5 G1L2 1.49845 81.15 0.240 1.0 G1L3 1.65803 39.46 0.119 G1L4 1.49845 81.15 0.240 3.2 G2 1.76859 26.3 0.112 16.2 G3 G3L1 1.72539 34.47 0.092 18.9 G3L2 1.88815 40.52 0.107 18.6 G3L3 1.70442 29.89 0.047 6.3 G3L4 1.49845 81.15 0.240 G4 1.62033 63.02 0.082 10.2 G5 G5L1 1.93429 18.74 0.553 1.0 G5L2 1.81643 22.57 0.286 G5L3 1.85504 22.59 0.153 11.9