JPS5918916A - Tessar type photographic lens - Google Patents

Abstract

PURPOSE:To obtain a small-sized lens whose aberrations are compensated excellently by providing the 1st-the 4th lens group which have a positive, a negative, a negative, and a positive refracting power from an object side successively, and allowing them to meet various specific requirements. CONSTITUTION:This lens system consists of the 1st meniscus positive lens having a convex surface on the object side, the 2nd biconcave lens with the negative refracting power, the 3rd lens with the negative refracting power, and the 4th biconvex lens with the positive refracting power successively from the object side. The 3rd and the 4th lenses are combined together into a lens having a positive refracting power. Then, this system meets requirements shown by inequalities I -VIII. In the inequalities R1 is the radius of curvature of the (i)th lens surface (i=1-8) successively from the object side and Di is the thickness and air gap of the (i)th lens (i=1-6); and Ni and upsiloni are the refractive index and Abbe number of the (i)th lens, and (f) is the focal length.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Tetsusar-type photographic lens, and is suitable for a Tetsusar-type 41 F lens with a rear aperture having an aperture at the rear of the lens in one row.

In a general camera, the entire camera is turned into a hut.

A Tetsusar type lens is extremely useful for simplifying the lens barrel structure.

In general, it is difficult to properly correct astigmatism and field curvature at intermediate angles of view with Tetsusar type lenses, which have a shooting angle of view of about 60°. This has the disadvantage that coma and flare become large from the middle to the peripheral angle of view.

SUMMARY OF THE INVENTION An object of the present invention is to provide a Tessar-type photographic lens that is compact and achieves good aberration correction.

The features of the lens configuration for achieving the object of the present invention are as follows: 9 lenses having a positive refractive power and having a positive refractive power with convex surfaces facing the object side; 9 lenses having negative refractive power with both lens surfaces being concave; , a third lens with a negative refractive power, and a fourth lens with both lens surfaces being convex, and the third lens and the fourth lens of No. 111 are laminated together to form a laminated lens with a positive refractive power. where R1 is the radius of curvature of the first lens surface from the object side, DI is the thickness and air distance of the first lens from the object side, and Ni and ν1 are the first lens surface from the object side, respectively.
When the refractive index of the glass of the th lens, the Atsube number, and f are the focal length (110, 13f<DI <0.2 F(2)' 0
．． 01 f<D2<0.05 f(3) 0.01
f<Ds<0.1 f(4) 0.35 f<R
t<0.39 f(5) 0.25 f<Re
<0.4 f(6) 1.75<N4 (force 48<ν1 (8) ν2×30).

In the photographic lens according to the present invention, in order to eliminate the drawback that the above-mentioned general Tetsusar type lens has a large amount of coma and flare from the middle part to the peripheral part of the screen, the thickness of the lens of the first lens is increased. At the same time, by increasing the radius of curvature of the object-side surface, and by arranging a glass with a high refractive index for the fourth lens and making the radius of curvature of the bonded surface an appropriate size, the above-mentioned coma and flare can be reduced. It is well corrected.

Next, the meaning of each of the above conditional expressions will be explained.

If the upper limit of conditional expression (1) is exceeded, the back focus becomes longer, making it difficult to downsize the photographic lens.If the lower limit is exceeded, it becomes difficult to reduce the Petzval sum, making it difficult to correct field curvature. become.

If the upper limit of conditional expression (2) is exceeded, coma aberration will be insufficiently corrected, leading to an insufficient peripheral illumination meter. Further, the lower limit value is a limit value for holding the lens when the total length of the lens is shortened by narrowing the air gap.

When the upper limit of conditional expression (3) is exceeded, introverted coma aberration increases at the periphery of the screen, and when the lower limit is exceeded, negative astigmatism increases.

If the upper limit of conditional expression (4) is exceeded, the back focus will become long, making it difficult to obtain a compact photographic lens.If the lower limit is exceeded, the spherical aberration will be undercorrected and the bulge in the middle of the spherical aberration will become large, which is not desirable. . If the upper limit of conditional expression (5) is exceeded, it becomes difficult to correct comatic aberration, and if the lower limit is exceeded, the refractive power of the junction becomes too strong, resulting in insufficient correction of the meridional field curvature.

When the range of conditional expression (6) is exceeded, the Petzval sum increases and the negative spherical field curvature at the middle of the two frames becomes large.

If the range of conditional expression (7) is exceeded, it becomes difficult to correct chromatic aberration of magnification.

If the range of conditional expression (8) is exceeded, it becomes difficult to correct axial chromatic aberration.

By satisfying the above-mentioned conditions, the present invention can provide a compact photographic lens that achieves good aberration correction.

Furthermore, in the present invention, better aberration correction can be achieved by arranging the diaphragm behind the final lens or near the branch lens.

In particular, when focusing is performed by arranging one lens behind the last lens and moving all the front lens groups, this is preferable because it is easier and simpler.

In the photographing lens according to the present invention, focusing may be performed by moving the entire lens, or by moving the first lens or the second lens and the second lens integrally.

Next, a numerical example of the present invention will be shown. In numerical examples R
1 is the radius of curvature of the #1 lens surface in order from the object side,
Di is the thickness and air gap of the first lens from the object side, and Ni and ν1 are the refractive index and Abbe number of the glass of the first lens from the object side, respectively.

Numerical Example 1 F=100 FNO=1 + 2.8 2W=
55.3゜Curvature radius Lens thickness/distance Refractive index
Atsube number R1 = 36.423 DI = 15
．． 58 N1=177250 Si1=49
．． 612=96.043 D2=2.
34R3=-128,433D3=4.67
N2=1.72151 ν2=29.2R4=
32.471 D4=3.17R5=
162.980 1) 5= 1.89 N
5=1.58144 shi3:40.7R6=
33.080 D6=IO, 19N4=1.8
0610 Shi4=40.9R7=-73,73
6 Back focus - 73.781 Numerical example 2 F=100 FT'JO=1:2.8 2
W=693°R1=37.236 DI=16.
32 N1=1.77250 Si1=49.6R2
= IO2, 229D2= 2.79R3=-13
3,58803=4.36 N2=1.72825
ν2=28.5R4= 33.802 0
4-3.68R5= 153.790 D5=
189 N5=1.59551 shi3239
．． 2R6=36.840 D6=10.04
N4=1.80440 C4=39.6R7==
-75,492 Back focus -72,26 Numerical example 3 F=100 FNO=l:2.8 2W-5
9,3°R1= 36.656 I)1=13.2
4 N1-1.77250 1/1-49.6R2=
96.379 D2=3.26R3=-1
33,273D3=6.03 N2=1.72151
1/2=29.2R4=33.198
D4=3.07R5=155.643 05=1.88
N5=1.58144 1/3=40.7R6=
33.239 D6=9.10 N4. -1.8
0610 V4-40.9R7= -75,422 Back focus -7477

[Brief explanation of drawings]

FIG. 1 is a sectional view of a lens corresponding to Numerical Example 1 of the present invention, and FIGS. 2 and 3 are diagrams of various aberrations for an object at infinity. FIG. 4 is a sectional view of a lens corresponding to Numerical Example 2 of the present invention, and FIGS. 5 and 6 are diagrams of various aberrations thereof for an object at infinity. FIG. 7 is a sectional view of a lens corresponding to Numerical Example 3 of the present invention, and FIGS. 8 and 9 are diagrams of various aberrations thereof for an object at infinity. In the figure, ΔS is a sagittal image plane, and ΔM is a meridional image plane. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] (1) In order from the object side, there is a meniscus-shaped lens with a positive refractive power whose convex surface faces the object side, a second lens with a negative refractive power whose both lens surfaces are concave, a third lens with a negative refractive power, and both lenses. It has four lenses, including a fourth lens with a convex lens surface, and the third lens and the fourth lens are bonded together to form a bonded lens with positive refractive power. The radius of curvature of the lens surface, Di, is the thickness of the first lens and the air spacing, and r4: and ν1 are the refractive index of the glass of the first lens, respectively, from the object side.
, when f is the total focal length (1,13f (DI <0,2 t O,01r <D2 <0.05 (0,01f <Da <0.1 fo, 35 f < R+ <0.39 fo , 25
Satisfy the following conditions: f < Ra < 0.4 fl, 75 < N4 48〈ν1 ν2〈30! A timely Tetsusar-type photographic lens.