JPS59155819A - Photographic lens - Google Patents

Abstract

PURPOSE:To obtain a compact and bright lens by providing the first - the third group lenses having positive, negative and positive refractive powers, and the fourth group lens consisting of meniscus lens whose concave surface is turned to an object side, and satisfying prescribed conditions. CONSTITUTION:In order from an object side, the first group is a meniscus lens having a positive refractive power, whose convex surface is turned to the object side, the second group is a biconcave lens having a strong concave surface to an image side, and the third group is a biconvex lens, and the fourth group is a meniscus lens which has an aspherical surface on the surface of the object side, and whose concave surface is turned to the object side. Also, conditions of an inequality I - inequality VII are satisfied. In this regard, in the inequalities, Ri:Di:Ni:R7*:DELTAx(h):f123:f4:fA: and (f) denote the i-th radius of curvature, the center thickness of the i-th lens of the air space, a refractive index of the i-th glass, a near axis R of the seventh surface, an aspherical surface quality in the direction parallel to an optical axis of the seventh surface to a near axis spherical surface in a height (h) from an optical axis, a composite focal distance of the first, the second and the third groups,a focal distance of the fourth group, a focal distance of an air lens constituted of the first and the second groups, and a focal distance of the whole system, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has an angle of view of about 65 degrees, a wide angle, and an F number of F2.
It relates to a photographic lens that is bright (8.8) and compact with a telephoto ratio of about 1.

Recently, with the miniaturization of cameras, it is better to adopt a type with a shorter overall length. When a telephoto type wide-angle lens is used as opposed to a long focal length lens with a narrow angle of view, it generally causes an increase in off-axis aberrations such as distortion, astigmatism, and coma, which poses a problem.

Conventionally, as a lens of this kind, for example, the
31. % Kosho 52-48011. Special Public Service 56-5024
8 etc. are known. The angle of view of the Tokuko Publication No. 44-10831 is as narrow as that of a standard lens, and the Tokuko No. 52-40811.
The F number of Tokuko Sho 56-50248 is F4.5. F3
．． 6, which is a rather dark lens.

Also, the angle of view was 60 mm from the present applicant in Japanese Patent Application Laid-Open No. 56-94317.
We are applying for a lens with an F number of F2.8.

An object of the present invention is to provide a compact and bright lens that exceeds the above-mentioned lenses and has an angle of view of about 65 degrees, an F number of F2.8, and a telephoto ratio of about 1.

Niscus lens, the second group is a biconcave lens with a strongly concave surface on the image side, the third group is a biconvex lens, and the fourth group is a meniscus lens with an aspherical surface on the object side and a concave surface facing the object side. and the first ratio is Ni, the paraxial 'R't of the seventh surface
R7*, the aspheric amount of the seventh surface in the direction parallel to the optical axis with respect to the paraxial spherical surface at the height h from the optical axis is Δx (h), the first
．． 2. The combined focal length of the third group is 7' +23, the focal length of the fourth group is f, the focal length of the air lens consisting of the first and second groups is f^, and the focal length of the entire system is f. When (
1) ' 0.43 < f 123 / 1f4k
0.52 However, f4 < 0 (2) o7 < lf included 1/ f < 1.0 However, fh < 0 (4)
1. ' 7 s < N1 (5) 1.80 < N5 (6) 0.4 < D4 / (D4 + D5)
<0.6.

Next, regarding the distribution of numerical conditions for achieving the object of the present invention, there are conditions for correcting the astigmatism difference while shortening the overall length. When the lower limit is exceeded, the astigmatic difference increases,
The pincushion type distortion condition is a condition in which the air lens consisting of the first and second groups is effectively used to correct off-axis aberrations that are a problem with telephoto lenses. If the upper limit is exceeded, pincushion distortion and negative astigmatism will occur significantly, and if the lower limit is exceeded, inward coma aberration will occur significantly and spherical aberration will be overcorrected, which is not preferable.

Condition (3) is a condition regarding the aspheric surface of the 4 group of fringes, and is a condition for effectively correcting off-axis aberrations that cannot be corrected by the spherical system alone due to compactness. If the upper limit is exceeded, outward coma aberration will occur significantly, and if the lower limit is exceeded, positive distortion will occur significantly, making it impossible to obtain uniform image quality over the entire screen.

Condition (4) is a condition regarding correction of spherical aberration.

The first group is a positive meniscus lens, but when the lower limit is exceeded, the curvature becomes steeper and the spherical aberration increases, resulting in a decrease in contrast.

Condition (5) relates to image plane correction. When the lower limit is exceeded, the bulge in the middle part of the screen due to the curvature of field increases, and the image quality in the middle part of the screen deteriorates.

Condition (6) is related to the arrangement of the third group and relates to correction of off-axis aberrations. When the upper limit value is exceeded, inward coma aberration increases, and when the lower limit value is exceeded at the periphery of the screen, astigmatism and pincushion distortion aberration increase.

Condition (7) is a condition for effectively bringing out the effect of aberration correction by the aspherical surface of the fourth group, and is related to correction of coma aberration. If the upper limit is exceeded, outward comatic aberration will occur, and if the lower limit is exceeded, inward comatic aberration will occur, both of which are undesirable.

By satisfying the above conditions, it becomes possible not only to focus by moving the entire lens, but also to focus by moving the 1st, 2nd, and 3rd groups together.

Next, numerical examples of the present invention will be shown.

In the numerical table, R1 is the first radius of curvature, Di is the origin of the seventh surface, the coordinate in the direction of the optical axis is X, and the coordinate in the direction perpendicular to the optical axis is h. Aspheric coefficients A, B
, C, D, E, A', B'.

C' and D' are the aspheric expressions of the 7th surface %formula% It shows that the coefficient of

The specifications of each example are shown below.

Furthermore, R? ” and △x (Oy7 R7*), △x
(0,5R7*) is a value expressed as follows.

When h = 0.7 R7” △x (h) = △x (
0.7R7*) When h=0.5R7* △x(h)=△x
(0,5R7*) Lens cross-sectional views and longitudinal aberration diagrams for the above embodiments are shown in FIGS. 1 to 6.

FIG. 1.2.3 shows a cross-sectional view of the lens of Examples 1 and 2.3, and FIG. 4.5.6 shows a longitudinal aberration diagram of Examples 4 and 5.6.

In the figure, d and g are di and g-line spherical aberrations, M and S, respectively.
indicates meridional and sagittal image planes.

[Brief explanation of drawings]

Fig. 1.2.3 shows a cross-sectional view of the lens of Example 1.2.3 of the present invention, and Fig. 4.5.6 shows a longitudinal aberration diagram of Example 1.2.3. Applicant: Canon Co., Ltd.

Claims (1)

[Claims] The group is a biconcave lens with a strongly concave surface on the image side, the third group is a biconvex lens, and the fourth group is a meniscus lens with an aspherical surface on the object side and a concave surface facing the object side. and the first radius of curvature is Ri, the Rth is R7*, the aspheric amount of the seventh surface in the direction parallel to the optical axis with respect to the paraxial spherical surface at the height h from the optical axis is Δx (h), and the 1.2. Let the combined focal length of the 3rd group be f128, the focal length of the 4th group be fh, the focal length of the air lens consisting of the 1st and 2nd groups be fh, and the focal length of the entire system be f Time, (i) 0.43 < fa2s /1f41 < 0
．． 52 However, f<<. (2) 0.7 <1fit/ f <1. o
However, 1 person <0(S) 1.75 <N. (a 1.80<N3 (fall) 0.4<1)4/(D4+D,)<
A photographic lens characterized by having a diameter of 0.6.