JPH0227310A - Lens system for microfilm photographing - Google Patents

Abstract

PURPOSE:To realize an extremely compact lens which can correct satisfactorily an aberration although it has a comparatively wide view angle by constituting a lens system of lenses of five groups and seven pieces, and also, allowing it to satisfy specific conditions. CONSTITUTION:The lens system is constituted of the first group of the first positive lens whose object side is a convex face, the second group of a cemented lens of the second positive lens and the third negative lens, the third group of the fourth positive lens whose object side is a concave face and a meniscus, the fourth group of a cemented lens of the fifth negative lens and the sixth positive lens, and the fifth group of the seventh positive lens whose object side is a concave face. Also, when (f), f1 and f3, fA, d8, nu21 and nu22, and nu41, nu42 denote a focal distance of the whole system, focal distances of the first group and the third group, a composite focal distance of the third and the fourth groups, an air interval between the third and the fourth groups, Abbe numbers of object side and image side lenses of the second group, and Abbe numbers of object side and image side lenses of the fourth group, respectively, said lens system is allowed to satisfy conditional inequalities.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photographing objective lens system used in a microfilm photographing camera.

[Prior art and invention or problem to be solved l11f
] Up until now, microfilm cameras have mainly been capable of shooting A4 size originals on 16mm film in a single frame size, but recently, microfilm cameras have been able to shoot A4 size originals on 16mm film.
There is an increasing demand for double frame size for shooting on M film. Then, the photographic lens for this purpose also needs a reduction ratio of 1/25, and the angle of view 2ω = 35"
It becomes necessary to change the angle of view of the lens from about 2ω to 45@ to make the entire device more compact.

As a lens system for such microfilm photography,
For example, Japanese Patent Publication No. 51-39529 and Japanese Patent Publication No. 51-8
A lens system disclosed in Japanese Patent No. 931 is known. The former is a modified Gauss type lens with 6 elements in 4 groups and has an angle of view of 2ω = 46 degrees, while the latter has 7 elements in 5 groups with an angle of view of 2ω = 38 degrees, both of which are excellent lenses, but the former suffers from coma and distortion. The latter has the drawbacks of large astigmatism and distortion. SUMMARY OF THE INVENTION An object of the present invention is to provide a compact microfilm photographing lens system that provides good aberration correction despite having a relatively wide angle of view compared to conventional lenses.

[Means for Solving the Problems] The lens system for microfilm photography of the present invention includes, in order from the object side, a first group consisting of a first positive meniscus lens having a convex surface on the object side, a second positive lens, and an fjS3 negative lens. The second group consists of a positive cemented lens, the diaphragm, the third group consists of a meniscus fourth positive lens with its concave surface facing the object side, and the fourth group consists of a negative cemented lens of a fifth negative lens and a sixth positive lens. This is a compact lens system for microfilm photography characterized by comprising a fifth group consisting of a positive meniscus lens and a seventh positive lens with a concave surface facing the object side.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings. 1st
3, 5, and 7 are cross-sectional views showing the construction of the embodiment 4, respectively. Starting from the object side on the left, a first group consisting of a first positive lens having a convex surface on the object side, a second group consisting of a second positive lens and a third negative lens cemented to this lens, an aperture S, A third group consisting of a fourth lens of a positive meniscus lens with a concave surface facing the object side, a fourth group of a cemented lens consisting of a negative fifth lens and a positive sixth lens, and a positive meniscus lens with a concave surface facing the object side. It is a microfilm photography lens system consisting of 7 elements in 5 groups, including the 5th group consisting of the 7th lens. It is a lens system for film photography.

In such a lens system, the focal length of the entire system is f, the focal length of the first group is f I + the combined focal length of the third group S and the fourth group is fA, and the distance between the third and fourth lens groups is The axial air distance is d6 + the focal length of the third group is f 3 + the second
2. Calculate the numbers of the object-side lens and image-side lens of the group, respectively. ．． C22. 4. Change the numbers of the object-side lens and image-side lens of the fourth group. ．． If C4□, then f+fA ■ satisfies the conditional expressions 0.5≦≦2 and 5.

The above conditional expressions 〇, ■, and ■ each indicate the aberration range, and if the upper limit of conditional expression (■) is exceeded, the astigmatism difference becomes large and correction becomes difficult. Also, if the lower limit is exceeded, astigmatism,
Comatic aberration and distortion increase accordingly, and both become difficult to correct.

Furthermore, if the range of the above conditional expression (0) is exceeded, astigmatism increases and it becomes difficult to correct it.

Furthermore, the above conditional expression (2) relates to the correction of axial chromatic aberration and 9-power chromatic aberration, and if the range of the upper limit value and lower limit value is exceeded, it becomes difficult to simultaneously correct each axial chromatic aberration of 1-power magnification.

Next, first to fourth embodiments of specific lens systems for microfilm photography that satisfy these conditional expressions are shown in Tables 1 to 4, respectively. In addition, the configuration diagram of the lens system and the aberration curve diagram are shown in FIGS.
Shaft top surface spacing.

These are the refractive index and Abbe number of the glass material at the d-line in each plane.

Further, the numerical values of the above conditional expressions for the first to fourth embodiments are summarized in Table 5.

(Left below) Table 1 f=1. OFNO=4.5 Radius of curvature Distance between axial surfaces Refractive index (Nd) Abbe number (ν
d) ri 1.266 d, 0.01i4 N, 1.80100
ν, 46.54r, 6.798 d20.004 rff O,353 d, 0.125 N, 1.74400
ν244.93r4U, 580 d40.049 N, 1.76182 ν,
26.55r, 0.251 d, 0.092 d60.07+ r6-0.707 dy O, 089N4 t, 75690 ν4
:11.79r, -0, :159 +1. 0.029 ra -0,217 ds O,0:l:l Ns 1.78472
ν, 25.75r9-0.491 d+r+ 0.062 Ng 1.67790
Shiro 5: 1.38r,. -0,31:1 dll 0.025 r++ -0,624 d12 0.089 N, 1.71ko00 Schiff 53.9:1r, 2-0.180 Table 3 Table f=1. OFNO=4.5 Radius of curvature Distance between upper surfaces of shaft Refractive index (Nd) Abbe number (
νd) rl 1.277 6.8ko5 0, :145 0.534 0.218 0.708 -0.369 0.2]2 o, st.

-0,297 0,064 0,004 0, +25 0.047 0.092 0.071 0.089 0.029 0.022 0.061 0.025 N, 1.80100 1.7440O 1,78472 1, 7569O 1,7552O 1,65100 ν, 46.54 ν2 44.9:1 25.75 ν4 :11.79 ν5 27.51 White 55.78 -0. :168 Σd=0.717 f=1. 0 radius of curvature ri 2.207 -552.938 0, :146 -7.853 0.281 -0. :l[18 -0,225 -0,690 -0,287 -1,526 -0,796 FNO=4. 5 Axial spacing Refractive index (Nd) d, 0.064 N, 1.7885
0di O,004 d Euro, 0fu2 Nz 1.807
00d40.036 N:11.68300d,
0.091 d, 0.052 Atsube number (νd) ν, 45.68 ν, 39.79 Shu: 11.52 d, +1.020 d, 0.036 N, 1.70055
ν, :lO,lld+o O,040Ng
1.71:Ion 26 53.9:1d,,
0.004 d1□ 01 mouth 89 Ny 1.749
50 ν, 50.00Σd= 0.59
6 Table r2-25.175 0.004 0.278 0.088 0.01i4 -0.419 0.037 r+o -0,:151 d,, 0.004 Σd= 0.655 [Effect of the invention ] As seen in each of the above, although the lens system for microfilm photography of the present invention has a wider angle of view than conventional ones, various aberrations are suppressed in a well-balanced manner both in the center and the periphery of the screen. This lens system has excellent aberration correction. Also.

It is an extremely compact lens system with a short overall length.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a lens system showing the configuration of a first embodiment of the present invention. FIG. 2 is an aberration curve diagram of the lens system shown in FIG. 1. FIG. 4 is a cross-sectional view of a lens system showing the configuration of an embodiment. FIG. 4 is an aberration curve diagram of the lens system shown in FIG. 3 above. FIG. 5 is a sectional view of a lens system showing the configuration of a third embodiment of the present invention, FIG. 6 is an aberration curve diagram of the lens system shown in FIG. 5, and FIG. 7 is a fourth embodiment of the present invention. FIG. 8 is a sectional view of the lens system showing the configuration of the embodiment. FIG. 8 is an aberration curve diagram of the lens system shown in FIG. Patent applicant Minolta Camera Co., Ltd. Agent
Koyama 1) Mitsuru factor diagram Spherical aberration Masahiro stop J ``Point aberration diagram Figure distortion % ■ Surface Q again difference engineer yaw ratio, υ null difference distortion % ゛ 6

Claims (1)

[Claims] 1. In order from the object side, a first group consisting of a first positive lens having a convex surface on the object side, a second group consisting of a positive cemented lens of a second positive lens and a third negative lens, and an aperture. , a third group consisting of a meniscus fourth positive lens with a concave surface facing the object side, a fourth group consisting of a negative cemented lens of a fifth negative lens and a sixth positive lens, and a meniscus lens group with a concave surface facing the object side. A compact lens system for microfilm photography characterized by being composed of a fifth group consisting of seven positive lenses. 2, (1) 0.5≦(f_1+f_A)/f≦2.5 (2) d_6/f_3≦0.04 (3)-8≦(ν_2_1+ν_2_2)/2-ν_4
The lens for microfilm photography according to claim 1, which satisfies the following conditional expressions: _1+ν_4_2/2≦-2. However, f: Focal length of the entire system f_1: Focal length of the first group f_A: Combined focal length of the third and fourth groups d_6: On-axis air distance between the third and fourth groups f_3: Third lens Focal length of the group ν_2_1: Abbe number of the object side lens of the second group ν_2_2: Abbe number of the image side lens of the second group ν_4_1: Abbe number of the object side lens of the second group ν_4_1: Abbe number of the image side lens of the second group It is Abbe's number.