JPS6015616A - Compact photographic lens using aspherical surface - Google Patents

Abstract

PURPOSE:To obtain a compact photographic lens having <=1 telephoto ratio, an F number of 1:3.5, and a field angle of >=60 deg. by using an aspherical surface of the object-side face of the fourth lens. CONSTITUTION:In a photographic lens which consists of the first positive lens, the second negative lens, the third positive lens, and the fourth negative lens and has a 4-group and 4-lens constitution, an aspherical surface is used as the object- side face of the fourth lens. A front-group converging system consisting of the first, the second, and the third lenses is moved as one body to perform focusing. A ratio of the resultant focal length of the front-group converging system to the focal length of the fourth lens is set to -0.47--0.48.

Description

[Detailed description of the invention]

The present invention has an F number of about 1:3.5 and an angle of view of 6.
A lens system with 4 elements in 4 groups and a small number of lenses that covers a wide angle range of 0.06 or more, and by using an aspherical surface on the object side of the 4th lens, the telephoto ratio (from the image plane to the combined focal length of the lens system) The present invention relates to an extremely compact photographic lens with a ratio of (total lens length) of less than 1 and excellent performance. Conventionally, in order to make the telephoto ratio less than 1, a front group focusing system,
Although it uses a so-called telephoto type with a rear group divergence system, it is composed of 4 elements in 4 groups: positive, negative, positive, and negative. The fourth lens has an aspherical surface on its object side in order to have an F number of about 3.5 and a wide angle of view of 60" or more, and to effectively correct astigmatism, distortion, coma, etc. The lens system used is already known in Japanese Patent Application Laid-Open No. 56-94317.The present invention provides a focusing method by integrally moving a front group convergence system consisting of a first lens, a second lens, and a third lens. This is an improvement on the above-mentioned Japanese Patent Application Laid-Open No. 56-94317 for the purpose of adopting this method.When the front group focus is adopted, the diaphragm mechanism can be fixed without moving together with the lens system, etc.
There are many advantages in mechanical configuration, but on the other hand, if eccentricity occurs between the lens groups between the front group convergence system and the rear group divergence due to movement of the front group convergence system, various aberrations of the lens system will deteriorate. There are drawbacks that lead to The purpose of the present invention is to alleviate the effects of such eccentricity. It is characterized by the power distribution of the fourth lens constituting the rear group divergence system and the aspherical shape of the object-side surface of the fourth lens. That is, the ratio of the combined focal length of the front group focusing system to the focal length of the fourth lens is approximately -0.47 to -0.48, thereby weakening the power of the fourth lens to alleviate the influence of decentering. Furthermore, the aspherical shape of the object-side surface of the fourth lens does not weaken the effects of correcting various aberrations due to the aspherical surface. By making the aspherical surface as close to a spherical shape as possible, when eccentricity occurs, changes in the curvature of the surface for each ray of light incident on the aspherical surface are made small, thereby mitigating the effects on various aberrations. Specifically, the distance difference in the optical axis direction between the spherical surface and the aspherical surface formed by the paraxial radius of curvature at a height corresponding to 50% of the paraxial radius of curvature of the aspherical surface from the optical axis is calculated for the entire system. The ratio to the focal length is approximately 3.30X10-s to 4.0OX10'.
A four-element lens in four groups consisting of a second lens that is a biconcave negative lens, a third lens that is a biconvex positive lens, and a fourth lens that is a negative meniscus lens with an aspherical concave surface facing the object side. A lens system that focuses by moving a lens, a second lens, and a third lens together, the optical axis direction is set as the χ axis, the direction perpendicular to the optical axis is set as the y axis, and the traveling direction of light is set as positive, When the origin is the intersection of the vertex of the lens surface and the χ axis, and the paraxial radius of curvature of the surface is ``, the aspherical shape of the aspherical surface is a compact photographic lens using an aspherical surface expressed by, In order from the object side, the radius of curvature of the first surface is ri, and the radius of curvature of the first surface is
The data of the example when the entire system is converted to the focal length f = 100 is as follows, where the distance between the 2nd and 3rd lenses is dl, the refractive index of the i-th lens with respect to d-1ine is nl, and the Atsube number of the i-th lens is ν1. That's right.

[Example 11 f=100 F number 1: 3.5 Angle of view 2ω=6
2.4゜rI dl 'ni 1 29.903 8.644 +, 77250 4!
1.72 96.980 2.090 3 -221.777 3.435 1.8051B
25.44 52.467 6.612 5 83.610 5.267 1.58144 40
．． 86 -83.610 21.296 7 -15.892 5.725 1.49136 5
7.88 -22.613 7-plane aspheric coefficient = 0.898 A = -0,57359X10' B = 0.57955x
lo-'C=-0,28500X10-"D=0.5
5238XIO-12 [Example 2] f = 100 F f :/bar 1 : 3.5 tt
I angle 2ω=62.4'r+ d-nl vl l 30.469 8.572 1.77250 49
．． 72 104.726 1.972 3 -224.511 3.429 1.80518
25.44 56.281 7.229 5 B7.293 5.172 1.58144 40
．． 86 -87.293 21.488 7 -16.076 5.715 1.60729 4
9.28 -22.374 7-plane aspheric coefficient K = 0.913 A = -0,37996X10-' B = 0.32928
X10-'C=-0.16189X10-'D=0.
30333X10-”

[Brief explanation of the drawing]

1 and 2 are lens sectional views and aberration diagrams of Example 1 of the present invention, and FIGS. 3 and 4 are lens sectional views and aberration diagrams of Example 2 of the present invention. Patent applicant Asahi Optical Co., Ltd. Representative Toru Matsumoto Figure 3 Figure 4 Spherical aberration Hakuho difference Astigmatism Sine condition distortion aberration

Claims (1)

[Claims] l In order from the object side, a positive meniscus lens with its convex surface facing the object side, and a second lens that is a biconcave negative lens,
A lens consisting of 4 lenses in 4 groups, consisting of a third lens, which is a biconvex positive lens, and a fourth lens, which is a negative meniscus lens with an aspherical concave surface facing the object side, the third lens, the second lens,
This is a lens system that moves the third lens together for focusing, and the radius of curvature of the first surface is set to "1" in order from the object side.
, the first interplanar spacing is dI, the refractive index of the d-1ine lens is ni, the Abbe number of the i-th lens is ν, the optical axis direction is the χ axis, and the direction perpendicular to the optical axis is y. When the aspherical shape of the surface is expressed as , A compact photographic lens using an aspheric surface that satisfies the following data when the entire system is converted to a focal length of f=100. f=100 F number 1: 3.5 Both angles 2ω=6
2.4゜rI ' dl nl ν 1 29.903 B, 644 1.77250 49
．． 72 96.980 2.090 3 -221.777 3.435 1.80518
25.44 52.467 6.612 5 83.610 5.267 1.58144 40
．． 86 -83.610 21.296 7 -15.892 5.725 1.49136 5
7.88 -22.613 7-picture spherical coefficient = 0.898 A = -0,57359X10-' B = 0.57955
X10-'C=-0,28500X10-''D=0.
55238 4th side negative meniscus lens
A lens system that focuses by moving the first lens, second lens, and third lens together, in which the radius of curvature of the first surface is set to ri in order from the object side. , the first surface spacing is dl, and the i-th
Let the refractive index of the lens for d-1ine be nl, the Atsube number of the i-th lens be ν, and the optical axis direction be the χ axis,
If the direction perpendicular to the optical axis is the y-axis, the direction of light travel is positive, the origin is the intersection of the vertex of the lens surface and the χ-axis, and the paraxial radius of curvature of the surface is r, then the aspherical shape of the surface A compact photographic lens using an aspheric surface that satisfies the following data when the entire system is converted to a focal length of f=100, when expressed by the following formula. f=100 F number 1: 3.5 Both angles 2ω=6
2.4゜dl n 1 30.469 B, 572 1.77250 /1
9.72 104.726 1.972 3 -224.511 3.429 1.805]8
25.44 56.281 7.229 5 87.293 5.172 1.58144 /1
0.86 -87.293 21.488 7 -16.076 5.715 1.6072! ]
4! J, 28 -22.374 7-plane aspheric coefficient K = 0.913 A = -0,37996xlO' B = 0.3292gx
+o-'C=-0.16189x1. O-” D=0.
30333xlO-”