JPS5820006B2 - photo lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a standard lens having an angle of view of 47° and a deformation of Fl:2 being a mouse shape.

An object of the present invention is to provide a photographic lens that is a six-element lens system, has an extremely short overall length, has an extremely long back focus, and has high performance.

The photographic lens of the present invention has a lens configuration as shown in FIG.
Consists of a group lens, a second group lens, a third group lens that is a negative meniscus lens with its convex surface facing the object side, a fourth group lens that is a meniscus cemented negative lens, and a fifth group lens that is a positive lens. It is a modified Gaussian lens system consisting of 6 elements in 5 groups.

Further, from the object side, the distance between each surface is di, the radius of curvature of the cemented surface of the fourth group lens, which is a cemented lens, is r8, and this fourth
The refractive index of both lenses of the group lens is 141 n5, and the combined focal length of the first group lens and the second group lens is f1□.
This photographic lens is characterized in that it satisfies the following conditions, where f is the focal length of the entire system.

Among these conditions, condition (1) is a condition showing the main feature of the photographic lens of the present invention, and shows that the lens is so short that it has never been seen before.

In addition to this, the content of the present invention is to provide a lens system with a long back focus and to correct the distortion of various aberrations that occur at that time under the following conditions (2) to (5).

Among these conditions, Σdi is 0.19 in condition (2)
When fi = 1, the spherical aberration is well corrected, but the back focus becomes shorter, and when it becomes smaller than 0.14f, the back focus becomes longer, but the astigmatism is overcorrected for the spherical aberration. This is not desirable.

Conventionally, to correct various aberrations, a method has been adopted in which the distance from the front surface of the front group to the final surface is made narrower, and the distance from the rear group is made smaller.This method shortens the back focus. Moreover, this was also a major obstacle in shortening the total length of the lens base.

In the present invention, the back focus is achieved by keeping the length of the front group small as shown in this condition (2).

By increasing the length and satisfying conditions (3) to (5), each aberration is corrected in a well-balanced manner.

In condition (3), when f12 becomes smaller than 0.54f, higher-order spherical aberrations are overcorrected and flare increases.
When the value is smaller than 0.5f, the Petzval sum is a negative value, and the absolute value becomes too dog-like, resulting in an increase in field curvature.

If r8 takes a positive value in condition (4), coma aberration worsens and chromatic aberration of magnification becomes overcorrected.

In condition (5), when n5 n4 is 0.13, it becomes a dog.

If it becomes smaller than 0.09, chromatic aberration of spherical aberration becomes undercorrected, and if you try to correct this by changing the radius of curvature of each lens surface, coma aberration and Astigmatism worsens and cannot be properly corrected.

The objective lens system of the present invention can be obtained by satisfying each of the conditions as described above.
6) and condition (7) are set to satisfy the conditions, more well-balanced aberrations can be obtained.

(6) (15f < rl < 0.64 f(7)
(133f < r3 < 0.41 f This condition (6
In X7), if rl is smaller than 0.64f, higher-order spherical aberrations will be overcorrected and flare will increase.

Moreover, when r3 becomes a dog from 0.41f, the Petzval sum becomes a negative value, and the absolute value becomes too much a dog, resulting in an increase in field curvature.

Also, rl and r3 are 0.5 f and 0.33 f, respectively.
If it is smaller, higher-order spherical aberration will be insufficiently corrected and the back focus will become shorter.

Next, examples of the photographic lens of the present invention will be shown.

Example 1 where rl j r2...rll is the radius of curvature of each lens surface, dl, d2...atO is the thickness and lens spacing of each lens, nl, n2...n6 is the refractive index of each lens, C1. C2... Shiro is the Atsube number of each lens, and fB is the back focus.

As is clear from the above description and examples, the photographic lens of the present invention is a lens system in which the distance from the first surface to the last surface of the front group is shortened, the overall length is shortened, and the back focus is lengthened. As is clear from the aberration curves shown in FIGS. 6 to 6, this is a high-performance photographic lens.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the photographic lens of the present invention, and FIGS. 2 to 6 are aberration curve diagrams of each example.

Claims (1)

[Claims] 1. A first group lens and a second group lens, each of which is a positive meniscus lens with a convex surface facing the object side, and a third group lens of a negative meniscus lens with a convex surface facing the object side; The lens is composed of 6 elements in 5 groups, consisting of a meniscus-shaped cemented negative fourth group lens with its convex surface facing the image side, and a positive fifth group lens, and satisfies the following conditions. Featured photographic lenses. 0 (1) Σd ku0.55f i=' (2) 0.14f< Σd 〈0.19f-
1 (3) 0.5f<f12<0.54f(4) r
s < 0 (5) 0.09 < n5 n4 < 0-13
However, di is the distance between each lens surface sequentially from the object side, r
8 is the radius of curvature of the cemented surface of the fourth group lens, n4yn is the refractive index of both lenses of the fourth group lens, f12 is the composite focal length of the first group lens and second group lens, and f is the total system focal length. It is the focal length.