JPS5961813A - Gaussian type lens conststing of six elements in four groups - Google Patents

Abstract

PURPOSE:To obtain a titled Gaussian type lens which has a large field angle, large aperture ratio, and less variation in aberration by using lenses of four group i.e., a positive meniscus, negative meniscus-shaped comenting, negative cementing, and a positive meniscus, and satisfying a specific condition. CONSTITUTION:This lens system has the 1st- the 4th group I -IV in order. The 1st group I is the positive meniscus lens having the concave surface facing the 2nd group side and the 2nd group II is the negative meniscus-shaped cemented lens of a positive and a negative lens having a convex surface facing the 1st group side; and the 3rd group III is the negative cemented lens of a negative meniscus lens having the concave surface facing the 2nd group side and a positive meniscus lens having the concave surface facing the 2nd group side, and the 4th group IV is the positive meniscus lens having the concave surface facing the 3rd group side. Then, inequalities I -IV are satisfied. In the inequalities, (f) is the focal length of the whole system, fII is the focal length of the 2nd group II, and fI II is the composite focal length of the 1st and the 2nd groups I and II; and fII IV is the composite focal length of the 3rd and the 4th groups III and IV, and ri is the radius of curvature of the (i)th group counted from the 1st group side.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lens system with little change in aberrations over a wide magnification range, and more particularly to an enlargement lens or a close-up lens.

Generally, with an enlarger lens, the shorter the distance from the negative to the photographic paper, the better the workability, and the larger the aperture ratio, the easier it is to focus, so a lens with as short a focal length as possible and as bright as possible is required. However, when operability is pursued, various aberrations fluctuate rapidly over a wide range of magnifications, which poses a practical problem.

An object of the present invention is to provide a lens system that can have a wide angle of view, a large aperture, and less variation in aberrations by providing appropriate conditions to a Gaussian lens.

That is, the present invention sequentially provides the first group (I) and the second group (II).
), 3rd group (1), 4th g ¥ (IV), and the above first group
Group (I) is a positive meniscus lens (Ll) with a concave surface facing the second group side, and the second group (II) is made up of a positive lens (L2) and a negative lens (L3) bonded together, and is on the 1n side. A meniscus-shaped negative cemented lens with a convex surface, the third group (II
I) is a negative meniscus lens with a concave surface facing the second group side (
A negative cemented lens consisting of a positive meniscus lens (L5) with a concave surface facing the second group and a positive meniscus lens (L5) with the concave surface facing the second group;
IV) provides a Gaussian lens with 6 elements in 4 groups, each consisting of a positive meniscus lens (L6) with a concave surface facing the 3rd group side, and satisfying the following conditions. be.

fl) ], 3J'< IfUl < 1.7f(2
11,6< f IN/fmIv< 2t31 0.3
5 f < rl < 0.54 fl4+ 0.13
< rlo/ < 0.259 However, f: Focal length of the entire system fU: Focal length of the second group fIII' Combined focal length of the first and second groups fIII
V'' Composite focal length r1 of the 3rd and 4th groups: The above conditional expression will be explained below the radius of curvature of the first surface counting from the 1st group side.Condition (1) This is to improve aberrations while keeping the distance (the distance from the imaging point to the fourth group when parallel light is input from the side) above a certain value. By observing this condition, S'> 0.6 f (S'2 back focus) is achieved.When the lower limit is exceeded, the divergence of the second group (b) becomes strong, distortion and astigmatism become large, and aberration fluctuations due to changes in magnification become large. If the upper limit is exceeded, it becomes difficult to lengthen the back focus.

Condition (2) is a condition for maintaining a balance in the focal lengths of the group formed by the first and second groups and the group formed by the second and third groups around the aperture, and is set at either the upper or lower limit. Even if the lens deviates from this, it becomes particularly difficult to correct off-axis aberrations, making it difficult to obtain good performance over a wide magnification range.

Condition (3) is a positive meniscus lens (L
□) defines the radius of curvature of the surface farther from the second ￥f, and corrects spherical aberration and distortion. When the upper limit is exceeded, spherical aberration becomes overcorrected and negative distortion occurs. If the lower limit is exceeded, spherical aberration will be insufficiently corrected, positive distortion will occur, and it will be difficult to increase the aperture and widen the angle of view.

Condition (4) suppresses aberration fluctuations due to changes in magnification while correcting spherical aberration; exceeding the upper limit results in over-correction of spherical aberration, and below the lower limit, under-correcting; in both cases, the symmetry of the lens system is collapses and aberration fluctuations increase.

Next, examples of the present invention will be shown. In each embodiment, when used as an enlarging lens, the first group side is used as the photographic paper side, and when used as a close-up lens, the first group side is used as the object side.

Example 1 f=too Fno,=2.8 2ω=55.8
° Radius of curvature Core thickness Refractive index (Nd) Dispersion (νd) Example 2 f = 100 Fno, = 2.8 2ω = 56.8 ° Radius of curvature Core thickness Refractive index (Nd) Dispersion (νd) r3
39.0" d38.59 N21.8075
W, 35.5r6 -23.74 d62.64 N, 1.6398 C34.6
rfu 52.94 d, 5.38 N51.6890 shi549,
4r9-305.11 d++ 10.32 Na ], 6400 Shiro 5
8.6r,,)-49,80 Example 3 f==ioo Fno,==2.8 2ω=55.8
゜Curvature radius Core thickness Refractive index (Nd) Dispersion (νd)
Furthermore, when implementing the present invention, good results can be obtained if the following conditions are followed.

tel l r41 > 2f (7) 2f<1fml<8.51 However, ν1, ν2: Dispersion of the positive meniscus lens (Ll) of the first group and the positive lens (L2) of the second group, respectively r4: Second group Radius of curvature of the joint surface in the middle +'
The focal length condition (5) of the third group is for correcting chromatic aberration by using relatively high dispersion glass for the positive lenses (Ll) (L2). Condition (6) is for aligning the colors. Outside the range of conditions (5) and (6), the variation of chromatic aberration with respect to changes in magnification becomes large, making it impossible to obtain good performance.

Condition (7), in combination with conditions +1) and (2), is for suppressing aberration fluctuations while ensuring back focus. If the lower limit is exceeded, the refractive power of the second group will be strained and distorted.
This causes deterioration of field curvature. On the other hand, if the upper limit is exceeded, the divergence power of the third group becomes weaker and the ability to correct aberrations generated in the first and second groups becomes insufficient.

FIG. 1.2.3 is a cross-sectional view of lenses of Examples 1 to 3. Figure 4.7.10 shows the imaging magnification of 1/3 in Examples 1 to 3.
16 (in the case of an enlarger lens, the imaging magnification is calculated by inputting light from the photographic paper side), spherical aberration, astigmatism, and distorted magnification chromatic aberration are shown. Also, Section 5.8.1
FIG. 1 is a diagram showing various aberrations when the imaging magnification is 1/8.5 in each example. Furthermore, FIG. 6.9.12 shows various aberration diagrams when the imaging magnification is 1/3 in each example.

44. Brief description of the drawings Figures 1.2.3 are cross-sectional views of lenses of Examples 1 to 3, Figures 4.5.6 are various aberration diagrams at each imaging magnification of Example 1, and Figure 7 8.9 is a diagram of various aberrations at each imaging magnification of Example 2, and Figures 10.11 and 12 are diagrams of various aberrations at each imaging magnification of Example 3.

■・・・1st group ■・・・2nd group ■・・・3rd group ■・・・Group 4 Applicant: Minolta Camera Co., Ltd. J threshold, grain L fzm IiJe, LIIJL True music, color-accuracy L

Claims (1)

[Scope of Claims] 1. A first group, a second group, a third group, and a fourth group, in which the first group is a positive meniscus lens with a concave surface facing the second group; The first group consists of a positive lens and a negative lens.
A meniscus-shaped negative cemented lens with a convex surface facing the group side.
The third group is a negative cemented lens made by laminating a negative meniscus lens with a concave surface facing the second group and a positive meniscus lens with a concave surface facing the second group. A Gaussian lens with 6 elements in 4 groups, each consisting of a positive meniscus lens with a concave surface facing the side, and satisfying the following conditions = 1.31 < Ifllll
<1.7f. 1, 6 < f7 II /7 m+v < 20.3
57 <r, <o, s 41 0.13<r19/ <0.25 9 However, f 2 Focal length of the entire system f: Focal length of the 27th group ■ f: Combined focal length of the 1st and 2nd groups ■■ fIIIv: Combined focal length rI of the 3rd and 4th groups:
A Gaussian lens with 6 elements in 4 groups according to claim 1, characterized in that the radius of curvature of the i-th surface counting from the first group side is 2, and further satisfies the following conditions: 1r41>2f However, Vl, ν2: dispersion 6 of the positive meniscus lens of the first group and the positive lens of the second group, respectively, and further satisfying the following conditions, Claim 1 or 2 The 6 Gaussian lenses listed in the 41st edition: 2f × 1f [111 × 3.5f, where f: focal length of the third group■