US 4,099,849 AGrant

Wide Angle Objective

Issue Date:1978-07-11

•33 Claims

•3 Drawing Sheets

Abstract

This disclosure relates to a Wide Angle Lens of the retrofocus type having a new lens group arrangement which comprises from the object end to the image end a first negative group, a second negative group in the form of a meniscus having a concave image side surface, a third positive group having a convex object side surface, a fourth positive group having a convex image side surface, a fifth negative group, and a sixth positive group having convex image and object side surfaces.

Metadata

Assignee

Vivitar Corporation

Inventors

John A. Lawson
Ellis I. Betensky

Application Information

Application Number:US 4924037

Filing Date:1974-07-29

Priority Date:1973-08-27

Art Unit:257

Classifications

IPC:

G02B 964

Field of Search:

350214

Patent Drawings (3 sheets)

Description

This invention relates to lenses, and more particularly to those known as wide angle lenses of the retrofocus type.

Wide angle lenses may be defined as those in which the diameter of the film or image frame of the camera with which the lens is used is substantially equal to or greater than the equivalent focal length of the lens. Moderately wide angle rectrofocus objectives covering field angles of approximately 80.degree. have been known for many years. Typically these lenses have been large in length and diameter resulting in considerable manufacturing expense and a lack of portability. In order to reduce the size, it is necessary to increase the lens element powers which normally increase the lens surface aberration contributions. When wide angle objectives of reduced size configuration are constricted to relative apertures of f/2.8, the need to correct large aperture dependence aberrations is apparent; however, when relative apertures of approximately f/2.0 or greater are desired, the amount of zonal spherical aberration and aperture dependent coma is considerably increased. Moreover, due to the large lens element powers, the amount of field curvature of third order and greater becomes excessive. Even though the aperture dependent aberrations may be well corrected, the zonal field curvature and astigmatism will severely limit resolution.

The present invention provides a new and improved lens configuration for wide angle objectives through the employment of a new lens grouping arrangement which minimizes the lens element powers in order to obtain the necessary back focal distance and front vertex distance as required to be useful in single lens reflex cameras. The minimization of the lens group powers decreases the surface contributions to distortion and various aberrations.

Briefly stated, a wide angle lens embodying the invention comprises a first lens group from the object end to the image end which is afocal, a second diverging group, third and fourth converging groups, a fifth diverging group and a sixth converging group. The lens groups and elements, and particularly the fourth group, have relative powers and configurations to achieve the objects of the invention, as hereinafter more specifically pointed out.

An object of this invention is to provide a new and improved wide angle lens of the retrofocus type.

Another object of this invention is to provide a lens of the type described of large relative aperture with minimized field curvature and astigmatism.

A further object of this invention is the provision of a lens of the type described having the capability of focusing to very close object distance without introduction of unacceptable field curvature and astigmatism.

The features of the invention which are believed to be novel are particularly pointed out and distinctly claimed in the concluding portion of this specification. However, the invention both as to its organization and operation, together with further objects and advantages thereof, may best be appreciated by reference to the following detailed description taken in conjunction with the drawings, wherein:

Figs. 1 - 3 are side elevations of lens embodying the invention;

FIGS. 4 and 5 are curves illustrating the improved performance of the lens of FIG. 1;

FIGS. 6 - 10 are side elevations of additional lens embodying the invention; and

FIGS. 11 and 12 are curves illustrating the improved performance of the lens of FIG. 8.

In all lens designs, the elemental groupings and spacings thereof are chosen to minimize aberrations and distortion of the overall lens and generally provide a true image of an object. The lens groupings are chosen to provide a lens of given field angle or equivalent focal length for a specified image quality. Therefore, the contribution of each lens group or element in multi-element lens is incapable of precise definition inasmuch as all lens configurations are selected in view of the others to provide the desired result.

The objects of the present invention are achieved by the provision of a new grouping of lens elements as hereinafter described.

A lens embodying the invention as disclosed comprises six lens groups from the object end to the image end as follows:

I. a two element group of negative power.

Ii. a meniscus of negative power.

Iii. a positive element having a convex front surface.

Iv. a positive element or doublet having a concave front surface and a convex rear surface.

V. a meniscus of negative power, and

Vi. a positive doublet.

A first lens 10 embodying the invention is set forth in FIG. 1, and comprises nine lens elements L1 - L9, arranged in six lens groups. The surfaces of the elements L1 - L9 are defined in radii R1 - R16 as shown. The first group viewed from the object end to the image end comprises elements L1 and L2 which are, as a combination, afocal with respect to the equivalent focal length (EFL) of the overall lens. The second group II is comprised of a meniscus L3 of negative power (diverging). The third group III is comprised of a biconvex element L4 of positive power (converging). The fourth group IV is comprised of a contacting doublet L5 and L6 of positive power (converging). The fifth group V is comprised of a negative meniscus (diverging) and the sixth group VI is a contacting doublet of positive power (diverging). This lens is defined by the data set forth in Table I.

A second lens 11 embodying the invention is set forth in FIG. 2 and comprises lens elements L1 - L8, arranged in six groups of the same relative powers as the lens of FIG. 1. Lens 11 differs from lens 10 primarily in that Group IV comprises a single element L5, but which is still of positive power (converging). Lens 11 is defined by the data set forth in Table II.

Another lens 12 is shown in FIG. 3 and comprises the six group I - VI of the same relative power as lens 11, having eight elements L1 - L8. The lens surfaces are defined on radii R1 - R15 as shown. Lens 12 differs from lens 11 primarily in that Group VI, elements L7 and L8, is comprised of a meniscus and a contacting bi-convex element in that order, rather than vice-versa, as lens 11. Lens 12 is defined by the data as set forth in Table III.

In the tables the index of refraction is denoted as N.sub.d and the dispersion as referenced by the Abbe number is denoted by V.sub.d.

Table I sets forth data on lens 10 of FIG. 1 scaled to an EFL of 28.7mm for a 24 .times. 36mm image frame, and having a relative aperture of F/1.9.

Table II sets forth data on lens 11 of FIG. 2 scaled to an EFL of 28.7mm for a 24 .times. 36mm image frame, and having a relative aperture of F/2.0.

Table III sets forth data on lens 12 of FIG. 3 scaled to an EFL of 28.7mm for a 24.times.36mm image frame and having a relative aperture of F/2.0.

In the examples of Tables I - III, all lens have a rated EFL of 28mm and a rated equivalent aperture of F/1.9, as scaled to a film or image frame size of 24 .times. 36mm. The lenses may, of course, be scaled to other image frame sizes, and EFL's.

FIGS. 4 and 5 exemplify plots of image height versus focal plane shift for the lens of FIG. 1, and a known wide angle lens scaled to 28mm EFL and a stated relative aperture of F/2.0, respectively, as shown in U.S. Pat. No. 3,736,049. Comparisons were made at a magnification of M = - 0.025 for a half image height of 20mm, for both sagittal S and tangential T rays.

The curves of FIG. 4 are relatively close together evidencing essential elimination of astigmatism. The curves of FIG. 4 have less deviation from the vertical, and are generally flatter than those of FIG. 5, to evidence a substantial reduction in field curvature.

The lenses of Tables I, II and III are designed for the first group elements L1 and L2 to be stationary while the rear elements are shifted in fixed relation as a group for focusing, as disclosed and claimed in the copending application of John A. Lawson, Ser. No. 492,413, filed July 29, 1974.

However, the lens Groups may also be arranged to move differentially as in the conventional wide angle objectives. For example, the entire objective may be shifted for focusing, while the fourth and fifth lens Groups move differentially in a well known manner. Also, the lens may be arranged to move only Groups V and VI for focusing, as disclosed and claimed in U.S. Pat. No. 3,975,090.

Further examples of lenses embodying the invention are set forth in FIGS. 6 - 10, and Tables IV - IX. In all of the examples, Group IV is an air spaced doublet L5, L6.

Table IV sets forth data on the lens 13 of FIG. 6 as scaled to an EFL of 28.5mm for a 24 .times. 36mm image plane, and having a relative aperture of F/1.9.

Table V sets forth data on a lens 14 substantially as shown in FIG. 7 scaled to an EFL of 28.6mm for a 24 .times. 36mm frame size and a relative aperture of F/1.9.

Table VI sets forth data on lens 15 of FIG. 8 scaled to an EFL of 35.0mm for a 24 .times. 36mm image frame, and a relative aperture of F/2.0.

Table 7 sets forth data on lens 16 of FIG. 9 scaled to an EFL of 35.0mm for a 24 .times. 36mm image frame, and a relative aperture of F/1.9.

Table VIII sets forth data on lens 17 of FIG. 10 scaled to an EFL of 35.0mm for a 24 .times. 36mm image frame, and a relative aperture of F/1.9.

Table IX sets forth data on a lens substantially as shown in FIG. 7 scaled to an EFL of 28.5mm for a 24 .times. 36mm frame size and a relative aperture of F/1.9.

FIGS. 11 and 12 exemplify further comparison of the focal plane shift of the lens of FIG. 8 and the lens of the previously mentioned patent at a magnification of M = - 0.025 for a half image height of 20mm, for both sagittal S and tangential T rays.

The curves of FIG. 11 are relatively close together evidencing substantially less astigmatism than FIG. 12. The curves of FIG. 11, particularly in the saggital have less deviation from the vertical, evidencing reduction in field curvature.

As previously mentioned, the contribution of each lens group to an overall lens is incapable of precise definition since properties of one or more elements and groups serve the same function and are complimenting and supplementing each other. However, in the new lens form described, Group IV is designed to provide certain contributions to the overall lens.

Group IV provides a substantial correction for the Petzval sum of the lens. The axial spacing of the front and rear surfaces contributes to correction of field curvature convex toward the object. Additionally, it provides positive power required to shorten the EFL of the overall lens while maintaining the required back focal length (BFL) to make the lens of the retrofocus type. The EFL of Group IV (F.sub.4) should have the following relation to the EFL of the overall lens (F.sub.o).

The foregoing is a critical relation, and other preferred relationships exist which do not have the same criticality. The radius R.sub.r4 of the rear surface is less than F.sub.o, or

This relationship contributes to correction for distortion. The axial separation D.sub.4 between front and rear surfaces is a substantial percentage of the EFL of the lens and preferably is in the range of

Additionally, to maintain the desired power contribution the combined EFL of Groups III and IV (F.sub.34) is preferably

As shown Group IV may be a single element or a doublet, either cemented or air spaced. It might also be defined in three elements. The front surface of Group III, L4, is convex. However, the rear surface may be other than convex depending on the design.

Groups V and VI are of positive power of a magnitude determined by the power of the other elements but in the preferred designs have an EFL (F.sub.56)

while the EFL (F.sub.6) of Group VI is

group III is of positive power to supplement the positive power of Group IV and preferably has an EFL (F.sub.3) range

The ranges set forth above may be better appreciated in consideration with Table X which tabulates the ratio of the EFL of each group and combinations thereof to the overall EFL of the lens.

The lenses disclosed may be focused on an object as close as 6.25 EFL's or less than seven inches in the case of the lens of Table IV. In the case of the lens of Table I, the lens is focused to 6.37 EFL or 7.02 inches with minimal astigmatism and field curvature, as exemplified in FIG. 4.

Table XI exemplifies the close focusing capability of the various lens disclosed.

It may thus be seen that the objects of the invention set forth above as well as those made apparent are efficiently attained. The invention provides a new wide-angle lens of the retrofocus type having a large relative aperture which will focus to an object distance of less than seven EFL's with minimal astigmatism and field curvature.

While preferred embodiments of the invention have been set forth for purposes of disclosure, other embodiments and modification to the disclosed embodiment of the invention may be derived by others skilled in the art. Accordingly, the appended claims are intended to cover all embodiments and applications of the invention and reversals thereof which do not depart from the spirit and scope of the invention.

Claims

What is claimed is:

1. A lens of the retrofocus type which comprises a plurality of lens elements arranged in six groups along a common optical axis from the object end to the image end as follows: a first group of negative power including positive and negative lens element, a second negative group in the form of a meniscus having a concave image side surface, a third positive group having a convex object side surface, a fourth positive group having a concave object side surface and convex image side surface, a fifth negative group consisting of a meniscus having a convex object side surface, and a sixth positive group consisting of a biconvex doublet.

2. The lens of claim 1 further defined by where F.sub.o is the equivalent focal length of the overall lens, and F.sub.4 is the equivalent focal length of the fourth group.

3. The lens of claim 1 further defined by where F.sub.34 is the combined equivalent focal length of the third and fourth groups, and F.sub.o is the equivalent focal length of the overall lens.

4. The lens of claim 1 further defined in that the first surface of said fourth group is concave and the distance D.sub.4 between the first and last surface thereof is where F.sub.o is the equivalent focal length of the overall lens.

5. The lens of claim 1 further defined by where F.sub.o is the equivalent focal length of the overall lens and F.sub.6 is the equivalent focal length of the sixth group.

6. The lens of claim 1 further defined by where F.sub.3 is the equivalent focal length of said third group, and F.sub.o is the equivalent focal length of the overall lens.

7. The lens of claim 1 further defined by where F.sub.4 is the equivalent focal length of said fourth group and F.sub.o is the equivalent focal length of the overall lens.

8. The lens of claim 1 defined by substantially the following data as scaled to an equivalent focal length of 28.7mm. Axial Distance Lens Radius Between Surfaces N.sub.d V.sub.d ______________________________________ R1 38.387mm L1 2.435mm 1.5168 64.2 R2 18.755 8.5083 R3 -119.389 L2 7.167 1.7995 42.3 R4 -52.877 4.72-0.20 R5 18.178 L3 2.180 1.5831 59.5 R6 12.456 9.369 R7 49.0379 L4 2.159 1.8306 36.5 R8 -123.776 - 2.581 R9 -22.141 L5 6.000 1.7470 27.5 R10 -109.562 L6 5.774 1.7620 40.3 R11 -21.131 0.135 R12 55.725 L7 2.454 1.8467 23.8 R13 26.386 2.239 R14 76.751 L8 6.000 1.8042 46.5 R15 -22.374 L9 1.500 1.8052 25.5 R16 -54.363 ______________________________________ where L1-L9 are successive lens elements arranged in six groups, L1, L2; L3; L4; L5, L6, L7; and L8, L9; R1-R16 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N.sub.d and V.sub.d are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.

9. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 28.7mm. Axial Distance Lens Radius Between Surfaces N.sub.d V.sub.d ______________________________________ R1 38.570mm L1 2.435mm 1.5168 64.2 R2 19.187 8.508 R3 -118.121 L2 4.797 1.7995 42.3 R4 -53.498 4.000-0.25 R5 18.556 L3 2.180 1.5831 59.5 R6 12.336 10.615 R7 50.120 L4 2.159 1.8306 36.5 R8 -160.5232 2.581 R9 -22.590 L5 10.883 1.7600 47.5 R10 -21.050 0.135 R11 51.8954 L6 3.257 1.8467 23.8 R12 26.298 2.239 R13 77.064 L7 7.000 1.8042 46.5 R14 -18.570 L8 1.500 1.8052 25.5 R15 -51.214 ______________________________________ where L1-L8 are successive lens elements arranged in six groups L1, L2; L3; L4; L5; L6; L7, L8; R1-R15 are the radii of curvature of the successive lens surfaces according to the sequence of the surfaces in the overall lens, N.sub.d and V.sub.d are the indexes of refraction and Abbe numbers, respectively, of the elements L1-L8.

10. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 28.7mm. Axial Distance Lens Radius Between Surfaces N.sub.d V.sub.d ______________________________________ R1 39.897mm L1 2.435mm 1.520 65.6 R2 19.832 8.500 R3 -111.180 L2 5.835 1.802 47.5 R4 -55.111 4.000-0.25 R5 17.557 L3 2.180 1.807 44.3 R6 12.193 10.789 R7 47.013 L4 2.433 1.833 41.8 R8 -138.976 3.390 R9 -23.286 L5 9.700 1.837 51.9 R10 -21.573 0.135 R11 51.904 L6 3.324 1.848 23.4 R12 26.009 2.682 R13 85.346 L7 1.000 1.848 23.4 R14 31.429 L8 4.000 1.776 50.6 R15 -43.746 ______________________________________ where L1-L8 are successive lens elements arranged in six groups, L1, L2; L3; L4; L5; L6; L7, L8; R1-R15 are the radii of curvature of the successive lens surfaces according to the sequence of the surfaces in the overall lens, N.sub.d and V.sub.d are the indexes of refraction and Abbe numbers, respectively, of the elements L1-L8.

11. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 28.5mm. Axial Distance Lens Radius(mm) Between Surfaces(mm) N.sub.d V.sub.d ______________________________________ R1 155.101 L1 4.160 1.562 58.52 R2 -541.744 .300 R3 29.242 L2 3.000 1.487 70.4 R4 13.031 12.759 R5 22.898 L3 2.000 1.800 42.3 R6 15.520 8.692 R7 48.249 L4 3.200 1.785 25.7 R8 -70.561 1.967 R9 -24.204 L5 2.164 1.805 25.5 R10 -1430.264 .844 R11 -94.529 L6 5.504 1.800 42.3 R12 -19.767 3.550-1.028 R13 45.215 L7 2.580 1.847 23.8 R14 29.179 1.700 R15 70.687 L8 8.00 1.743 49.2 R16 -19.969 L9 2.700 1.847 23.8 R17 -44.577 ______________________________________ where L1-L9 are successive lens elements arranged in six groups, L1,L2; L3; L4; L5,L6; L7; L8,L9; R1-R17 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N.sub.d and V.sub.d are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.

12. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 28.6mm. Axial Distance Lens Radius(mm) Between Surfaces(mm) N.sub.d V.sub.d ______________________________________ R1 42.160 L1 5.700 1.487 70.4 R2 384.104 .300 R3 35.935 L2 2.800 1.487 70.4 R4 11.488 4.032 R5 26.721 L3 2.000 1,517 64.2 R6 15.510 14.343 R7 39.692 L4 3.200 1.689 31.2 R8 925.392 2.973 R9 -76.847 L5 2.164 1.847 23.8 R10 97.091 1.750 R11 -75.162 L6 4.549 1.800 42.3 R12 -21.352 4.098-.100 R13 37.634 L7 2.700 1.722 29.2 R14 32.248 2.000 R15 70.613 L8 8.400 1.641 59.8 R16 -18.940 L9 2.700 1.805 25.5 R17 -42.358 ______________________________________ where L1-L9 are successive lens elements arranged in six groups, L1,L2; L3; L4; L5,L6; L7; L8,L9; R1-R17 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N.sub.d and V.sub.d are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.

13. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 35.0mm. Axial Distance Lens Radius(mm) Between Surfaces(mm) N.sub.d V.sub.d ______________________________________ R1 31.195 L1 2.998 1.517 64.2 R2 20.569 7.074 R3 -96.642 L2 2.829 1.785 25.7 R4 -58.277 0.726 R5 18.356 L3 4.321 1.723 38.0 R6 12.649 11.925 R7 53.996 L4 2.800 1.831 36.5 R8 -172.838 3.000 R9 -22.950 L5 2.695 1.741 27.8 R10 -276.177 0.720 R11 -76.849 L6 6.081 1.757 47.7 R12 -19.800 2.000-0.20 R13 51.599 L7 3.000 1.847 23.8 R14 31.353 2.332 R15 82.914 L8 7.000 1.800 42.3 R16 -25.647 L9 3.000 R17 -57.034 1.805 25.5 ______________________________________ where L1-L9 are successive lens elements arranged in six groups, L1,L2; L3; L4; L5,L6; L7; L8,L9; R1-R17 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N.sub.d and V.sub.d are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.

14. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 35.0mm. Axial Distance Lens Radius Between Surfaces N.sub.d V.sub.d ______________________________________ R1 598.84mm L1 4.160mm 1.750 35.0 R2 -175.71 .300 R3 22.57 L2 2.985 1.487 70.4 R4 13.99 9.079 R5 23.40 L3 5.005 1.700 47.8 R6 15.49 8.869 R7 58.80 L4 3.200 1.831 36.5 R8 -100.28 2.385 R9 -24.54 L5 2.358 1.741 27.8 R10 -845.99 .680 R11 -102.81 L6 6.778 1.757 47.7 R12 -19.97 0.91-3.66 R13 58.83 L7 3.000 1.847 23.8 R14 32.65 1.700 R15 65.28 L8 7.300 1.800 42.3 R16 -27.00 L9 0 1.805 25.5 R17 -79.24 ______________________________________ where L1-L9 are successive lens elements arranged in six groups, L1,L2; L3; L4; L5,L6; L7; L8,L9; R1-R17 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N.sub.d and V.sub.d are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.

15. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 35.0mm. Axial Distance Lens Radius(mm) Between Surfaces(mm) N.sub.d N.sub.d ______________________________________ R.sub.1 30.600 L1 7.000 1.487 70.4 R2 170.290 .300 R3 34.231 L2 2.985 1.487 70.4 R4 11.567 6.000 R5 67.235 L3 2.000 1.569 56.0 R6 25.201 6.171 R7 46.077 L4 3.200 1.806 40.7 R8 -644.608 7.931 R9 -34.424 L5 2.358 1.762 26.6 R10 -829.911 1.350 R11 -47.763 L6 4.832 R12 -19.289 1.757 47.7 4.70-.10 R13 41.514 L7 3.000 1.667 33.1 R14 35.544 1.900 R15 64.725 L8 8.000 1.717 48.0 R16 -22.414 L9 2.700 1.805 25.5 R17 -56.648 ______________________________________ where L1-L9 are successive lens elements arranged in six groups, L1,L2; L3; L4; L5, L6; L7; L8,L9; R1-R17 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N.sub.d and V.sub.d are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.

16. The lens of claim 1 defined substantially by the following data as scaled to an equivalent focal length of 28.5mm. Axial Distance Lens Radius(mm) Between Surfaces(mm) N.sub.d V.sub.d ______________________________________ R1 54.600 L1 5.700 1.487 70.4 R2 937.48 .300 R3 28.640 L2 2.800 1.487 70.4 R4 11.392 4.474 R5 28.640 L3 2.000 1.517 64.2 R6 15.990 13.502 R7 41.450 L4 3.200 1.689 31.2 R8 840.70 3.342 R9 -70.750 L5 2.164 1.805 25.5 R10 106.030 1.900 R11 -71.649 L6 4.549 1.804 46.5 R12 -21.220 4.098-.10 R13 48.140 L7 2.700 1.741 27.8 R14 35.430 1.212 R15 53.960 L8 9.159 1.639 55.5 R16 -20.430 L9 2.700 1.805 25.5 R17 -44.190 ______________________________________ where L1-L9 are successive lens elements arranged in six groups, L1,L2; L3; L4; L5,L6; L7; L8,L9; R1-R17 are the radii of curvature of the successive lens surfaces according to sequence of the surfaces in the overall lens, N.sub.d and V.sub.d are the indexes of refraction and Abbe Numbers, respectively, of the elements L1-L9.

17. the lens of claim 1 further defined by where F.sub.34 is the combined equivalent focal length of the third and fourth groups, and F.sub.o is the equivalent focal length of the overall lens.

18. The lens of claim 2 further defined in that the axial distance D.sub.4 between the first and last surface of said fourth group is where F.sub.o is the equivalent focal length of the overall lens.

19. The lens of claim 2 further defined by where F.sub.3 is the equivalent focal length of said third group, and F.sub.o is the equivalent focal length of the overall lens.

20. The lens of claim 2 further defined by where F.sub.o is the equivalent focal length of the overall lens and F.sub.6 is the equivalent focal length of the sixth group.

21. The lens of claim 1 further defined by where F.sub.4 is the equivalent focal length of said fourth group, F.sub.34 is the combined equivalent focal length of said third and fourth groups and F.sub.o is the equivalent focal length of the overall lens.

22. A retrofocus lens consisting of nine elements and from the object side comprising a first two element group including a positive and a negative lens element of overall negative power, a third element in the form of a negative meniscus having a convex object side surface, a fourth positive element having a convex object side surface, fifth and sixth elements, said fifth element having a concave object side surface and said sixth element having a convex image side surface, said fifth and sixth elements being of overall positive power, a seventh element in the form of a negative meniscus having a convex object side surface, and eighth and ninth elements cemented together and being overall bi-convex.

23. The lens of claim 22 further defined by where F.sub.34 is the combined equivalent focal length of the third and fourth groups, and F.sub.o is the equivalent focal length of the overall lens.

24. The lens of claim 22 further defined in that the axial distance D.sub.4 between the first and last surface of said fourth group is where F.sub.o is the equivalent focal length of the overall lens.

25. The lens of claim 22 further defined by where F.sub.3 is the equivalent focal length of said third group, and F.sub.o is the equivalent focal length of the overall lens.

26. The lens of claim 22 further defined by where F.sub.o is the equivalent focal length of the overall lens and F.sub.6 is the equivalent focal length of the sixth group.

27. A retrofocus lens consisting of eight elements and from the object side comprising a first two element group including a positive and negative lens element of overall negative power, a third element in the form of a negative meniscus having a convex object side surface, a fourth positive element having a convex object side surface, a fifth positive element having a concave object side surface and a convex image side surface, a sixth element in the form of a negative meniscus having a convex object side surface, and seventh and eighth elements cemented together and being overall bi-convex.

28. A lens of the retrofocus type which comprises from the object end a first group of a positive and a negative element of overall negative power, a second group of negative power in the form of a meniscus having a concave image side, a third group of positive power having a convex object side surface, a fourth positive group comprising two elements and having a concave object side and a convex image side, a fifth group and a sixth group, said fifth group consisting of a negative meniscus having a convex object side surface, said sixth group consisting of a biconvex doublet.

29. The lens of claim 28 further defined by where F.sub.34 is the combined equivalent focal length of the third and fourth groups, and F.sub.o is the equivalent focal length of the overall lens.

30. The lens of claim 28 further defined in that the axial distance D.sub.4 between the first and last surface of said fourth group is where F.sub.o is the equivalent focal length of the overall lens.

31. The lens of claim 28 further defined by where F.sub.3 is the equivalent focal length of said third group, and F.sub.o is the equivalent focal length of the overall lens.

32. The lens of claim 28 further defined by where F.sub.o is the equivalent focal length of the overall lens and F.sub.6 is the equivalent focal length of the sixth group.

33. The lens of claim 28 further defined by where F.sub.o is the equivalent focal length of the overall lens, F.sub.34 is the combined equivalent focal length of the third and fourth groups, D.sub.4 is the axial distance between the front and rear surfaces of the fourth group, F.sub.3 is the equivalent focal length of the third group, and F.sub.6 is the equivalent focal length of the sixth group.

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US3583791	1971-06-01	Mori
US3832037	1974-08-01	Nakagawa
US3856385	1974-12-01	Takahashi
US3870402	1975-03-01	Takahashi et al.
US3975090	1976-08-01	Lawson
DEX46,553	1966-03-01
ITX661,922	1964-04-01
JPX4,528,832	1970-09-01

Abstract

Description