JPS6010605B2 - Compact retrofocus wide-angle lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a long back focus 4-inch photographic objective lens for use in a single-lens reflex camera.

Retrofocus type wide-angle lenses have the advantage of being able to have a long back focus, but because the front group of this type of lens has strong divergent power, it is susceptible to distortion, coma, and halo of Sagittal Koto. The occurrence of various aberrations is significant.

Therefore, in order to deal with these aberrations, a method is adopted in which the lens arrangement of the rear group is made appropriate and at the same time the total length of the lens is lengthened to reduce the absolute amount of aberration occurring on each lens surface.

However, if we try to make the lens more compact, the curvature of the negative lens in the front group will inevitably become stronger, so in order to correct the various aberrations that occur with this negative lens, we need to place a corrective lens just in front of this lens. is also known, but in this case there is a drawback that the diameter of the front lens increases.

The present applicant previously filed an application for a wide-angle lens in which various aberrations are well corrected in Japanese Patent Laid-Open No. 51-29135. However, when the overall length of the lens described in this prior application was reduced by about 10% and the front lens was reduced, the halo of the sagittal light became particularly problematic. In order to compensate for this deterioration in image quality, it is conceivable to use special glass for the lens, but this has the disadvantage of increasing costs. An object of the present invention is to satisfactorily correct various aberrations including the sagittal optical halo by appropriately selecting the mutual arrangement of each lens.

FIG. 1 shows the cross-sectional shape of the lens according to the embodiment, and FIG. 2 shows various aberration diagrams for infinity, where ΔS is the sagittal line and ΔM is the total meridional point.

The lens arrangement consists of, in order from the subject side, two negative varnish lenses, a regular lens with a gentle curvature on the image side, a biconvex lens, a biconcave lens, and two positive varnish lenses. Numerical specifications will be described below, where P is the radius of curvature of the lens surface, D is the axial thickness of the resin or the distance between the resins, Nd is the refractive index for the d-line, and yd is the Abbe number for the d-line.

f=10F number 1:2. & Angle of view 2 = 7 plane number R D Nd yd1
79.151 5.79 1.60311 60.
72 44.593 14.21 13
85.091 4.56 1.60311
60.7 surface number R D Nd
Lid4 54.902 27.54 15
184.03 7.09 1.6989
5 30.16 -7813.7 19.86
17 120.79 12.35 1.77
25 49.68 -10745 11.33
19 -86.095 15.79 1.
80518 25.410 113.87
5.09 111 -131.19 7.4
7 1.713 53.912 -65814
0.7 113 -47944 8.14
1.7725 49.614 -96.35
1 120:139.92b. f=127.
3 (back force)

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a lens showing an embodiment of the present invention, and FIG. 2 is a diagram of various aberration curves of the embodiment. In the figure, R is the radius of curvature of the lens surface, and D is the thickness of the resin or the interval between the resin surfaces. Chrysanthemum 1, Kan 2

Claims (1)

[Claims] 1. In order from the object side, two negative meniscus lenses, a positive lens whose image side lens surface has a gentle curvature, a biconvex lens, a biconcave lens, and two positive meniscus lenses are arranged, and the focal length is f. A small retrofocus type wide-angle lens that satisfies the following numerical specifications when converted to =100. Surface number R D Nd νd1 79.151 5.7
9 1.60311 60.72 44.593 14
．． 21 13 85.091 4.56 1.6031
1 60.74 54.902 27.54 15 1
84.03 7.09 1.69895 30.16
-7813.7 19.86 17 120.79 1
2.35 1.7725 49.68 -107.45
11.33 19 -86.095 15.79 1
．． 80518 25.410 113.87 5.09
111 -131.19 7.47 1.713 5
3.912 -65.814 0.7 113 -47
9.44 8.14 1.7725 49.614 -
96.351 1 where R is the radius of curvature, D is the lens thickness or lens spacing, Nd is the refractive index for the d-line, and vd is the average number for the d-line.