JPS58121010A - Photographic lens - Google Patents

Abstract

PURPOSE:To make F-number brighter, and also to obtain a titled lens of a wide view angle and small size, by constituting a modified Tessar type lens provided with a lens shutter, by combining lenses of positive and negative refractive power. CONSTITUTION:A titled photographic lens consists of the first positive meniscus lens whose convex surface has been faced to an object side, the second biconcave lens, the third biconvex lens and the fourth negative lens in order from the object side, and on the circumference of the image surface of the combined lens, an aperture is provided. Also, as for a composite focal distance of the whole lens system, conditions as shown in the inequalities are satisfied. Where, Ri (i=1...), Di (i=1...), Ni (i=1...) and Vi (i=1...) denote a radius of curvature of the i-th lens surface in order from the object side, the i-th lens thickness and an air interval in order from the object side, a refractive index of glass of the i-th lens in order from the object side, and Abbe's number of the i-th lens in order from the object side, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photographic lens that is an improved version of the Tesser type lens and is equipped with a lens shutter.

As a photographic lens for a camera with a lens shutter,
A so-called rear diaphragm type Tetsusar type lens in which a diaphragm is disposed at the rear of the lens is usually available in a good quantity and is disclosed in Japanese Patent Application Laid-open No. 75611/1983.

However, in general, including these conventional examples, when looking at the distance from the lens surface to the focal point, which is a standard for the compactness of a photographic lens, that is, the ratio of the total lens length to the focal length f, the F number is FNo, = 2.8 class. With a shooting lens of 'f: 1iJ9, Ihb and Vt
: When a photographic lens was made smaller to about 1.06, it had to be relatively dark with an F number of 35.

The purpose of the present invention is to have a bright F number of 2.9.
The object of the present invention is to provide a photographic lens with a wide angle of view that is designed to be compact, and in the embodiment described later, a photographic lens with an angle of view of 2ω = 6f is achieved with Iy'f = about 1.06.

Characteristics of the lens configuration of the photographic lens to achieve the object of the present invention Starting from the object side, the second lens has a positive refractive power and has a meniscus shape with its convex surface facing the object side.JI1 has both lens surfaces concave.
42 lenses, and a laminated lens consisting of a third lens whose both lens surfaces are convex and a fourth lens with negative refractive power.
A diaphragm is provided in the glue Ii, and the radius of curvature %Di of the tllth lens surface is set as Ri in order from the object side to the i11th radius in order from the object side.
The lens thickness and air distance of the eye, Ni and νi, respectively from the object side to JJi, the refractive index of the glass of the first lens and Atsube's number 1, and the combined focal length of the entire lens system as f (1) 0
．． 25 < MS Ni < 0.4 (2) 0.
25<R, /f<0.33(3) 2<1Rs
l/% However, R3> 0(4) 0.26<R
,<0.35 (510,07<D1/f<0.1 (6) 0.06<"+D'< 0.15 (7)
It is to satisfy the following conditions: 20<v2<32 (8) lo<l/3-y, <3g.

The photographic lens according to the present invention focuses on the following points in order to simultaneously satisfy a widening of the photographing angle of view and a reduction in the overall length of the lens.

0) Reduce the Petzval sum.

←) Shorten the back focus of the lens.

e) Reduce the total thickness of the lens.

(Regarding the matter in (), h is made up of ordinary Tetsusar-type lens elements, but if the photographing lens element according to the present invention is bonded together, ν and 4 are approximately equal due to the requirements for correcting chromatic aberration. On the other hand, if a lens with positive and noble refractive powers is bonded together, ν, <ν4 can be obtained.

This has the advantage that when selecting the glass material, it is possible to set ν, N under the condition of <ν4,>N. 0
In order to achieve the above, the refractive power of the first lens can be made strong, but if it is made too strong, it tends to cause worsening of spherical aberration and distortion. Attempting to carry out the item e) tends to cause worsening of spherical aberration and comatic aberration, and also tends to increase curvature of field at the periphery of the screen. The photographic lens according to the present invention has the above-mentioned matters 0, 0. 5) The photographic lens according to the present invention achieves the object of the present invention by setting the above conditions (1) to (8) for each lens in the above lens configuration. Next, each of the above conditions will be explained. The conditional expression (ri) is to increase the refractive index difference between both lenses in the bonded lens of the third lens group and reduce the Petzval sum. The sagittal curvature of field increases in the negative direction at the middle of the screen, and when the upper limit is exceeded, the sagittal curvature of field increases in the positive direction at the periphery of one screen, and at the same time, inward comatic aberration occurs at the middle of the screen. Therefore, it becomes difficult to widen the angle of view.Conditional expression (2) makes it possible to reduce the sagittal image in the positive direction at the periphery of the screen, which tends to occur within the range of conditional expression (1), by making the angle relatively small. For improving surface curvature, if the upper limit of the same conditional expression is exceeded, it will be difficult to satisfactorily correct sagittal curvature of field in the positive direction at the periphery of the screen, and if the lower limit is exceeded, it will be difficult to correct spherical aberration. Conditional expression (3) indicates the range in which lR31 is made relatively large, suppressing the sagittal curvature of field at the periphery of the screen from increasing in the positive direction, and further correcting distortion aberration satisfactorily. If the limit of the same conditional expression is exceeded, the sagittal curvature of field at the periphery of the screen will increase, which is undesirable.Also, s R1&0
Conditional expression (3) is regulated as R, and when >o,
This is because positive distortion increases, which is undesirable. By making conditional expression (4) a and R+ relatively small, the back focus can be shortened, and spherical aberration, which is difficult to correct when the total lens thickness is made thin, can be effectively corrected. If the lower limit of the condition is exceeded, the correction of spherical aberration becomes a national problem, and the sagittal curvature of field at intermediate angles of view increases in the negative direction, and if the lower limit is exceeded, the annular spherical aberration increases, which is undesirable. . Conditional expression (5) reduces the total lens thickness by regulating the thickness of DI, and reduces the outer diameter of the lens of the first lens, thereby reducing the size of the entire lens.

Furthermore, improvements have been made in field curvature. If the upper limit of the conditional expression is exceeded, the outer diameter of the lens required for the first lens will become too large, making it difficult to downsize the photographic lens. In addition, the sagittal image plane is greatly curved in the positive direction at the periphery of the screen.Also, if the lower limit is exceeded, it becomes difficult to correct spherical aberration, which is undesirable.Conditional expression (6) is This is intended to reduce the size of the photographic lens in a well-balanced manner while correcting the inward coma aberration at intermediate angles of view that tends to occur in the range of 1). This is undesirable because the pole increases, making it difficult to downsize and increasing distortion, and if the lower limit is exceeded, inward coma aberration occurs at intermediate angles, which is undesirable.Conditional expression (7) is Axial chromatic aberration and lateral chromatic aberration can be well corrected.If the upper limit of the same conditional expression is exceeded, the axial chromatic aberration will be undercorrected and the lateral chromatic aberration in the positive direction will increase, and if the lower limit is exceeded, the axial chromatic aberration will be Chromatic aberration is not desirable because it is over-corrected and lateral chromatic aberration occurs in the negative direction.Conditional expression (8), along with conditional expression (7), is used to properly correct longitudinal chromatic aberration. If the upper limit of the conditional expression is exceeded, the longitudinal chromatic aberration will be insufficiently corrected9, and if the lower limit is exceeded, the longitudinal chromatic aberration will be corrected -aviI, which is undesirable.

As can be seen from the above description, the m-shade lens according to the present invention is bright, has a wide angle of view, and can be made small in size by satisfying the above conditions. For example, in the example described later, I, /f=IJ)6°2ω; 64 degrees,
When the focal length f=34 m, L=36-, which results in an extremely compact photographic lens with excellent aberration correction.

Further, in the photographic lens according to the present invention, focusing may be performed by taking out the entire lens, or by taking out only the 4th lens, or by taking out the 1st lens and the 1iA2 lens as a unit.

Next, a numerical example of the present invention will be shown. In the numerical example, the lens l is the i-th lens in order from the object side to the j'th lens.
These are the refractive index and Atsube number of the glass of the th lens.

Further, Table 1 shows the third-order aberration coefficients of Numerical Example 1. fi
As is clear from 1, the Petzval fO is usually about 0.25 behind in Tetsusar-type lenses with a rear aperture system, but with the photographic lens according to the present invention, it is possible to reduce it to about 0.16. becomes.

Numerical Example I R1=29.462 D1=8.456 N1=1
．． 81554 ν, = 444R2 = 72.071
D2=2.531, dR3=-319,172D
3=4.281 N2=1.76182ν, =26.6
R4= 27.965 D4=2.813R5=
64.760 D5=8.418 N5=1.7995
2νm=42-2R6=-38,777D6=2.3
57 N4=1.51112ν,=60.5R7=27
12.611 Focal length = 100 Back focus = 7 & 72 εD = 2 & 86 L = IQ5L6 Numerical example 2 R1 = 29.283 DI = 8.227 N1 = 1
．． 81554νyi=444R2= 70.596 D
2=2.514&3=-319,974D3=4.27
9 N2=L76182ν,=26.6R4=27
．． 931 D4=2.751R5=64.239
D5 = 8.378 N5 = L80610 = 40.9
R6=-39,624D6=2.337 N4=1.
50137 Shift = 56.4 R = 1003.658 Focal length = 100 L = 1015 Numerical example 3 R1 = 29.447 Dl = 7.641
N1=1.83481 1',=42.7R7=-
1281,498 Focal length = 100 Numerical example 4 R1 = 31.501 D1 = 8.516 N1 = 1
．． 83481ν, =42.7R7=264214 Focal length=100 L=106.8 Table 1! Lt
pRl 9.674-0.3780.01
41.524R20,270-0,6161,406-
0,62313-4,3763,668-3,074-
0,135R4-9,603-1,618-0,272
-1,546R51,803α953 Q, 5030.
686R64,021-1,6200,653α273
R70,403-0,565α794-0.012.1
2.193047-0.178479 0.0247
86 0.167097

[Brief Description of the Drawings] Fig. 1 is a cross-sectional view of the lens of Numerical Example 1 of the present invention, and Figs. 2 to 5 are various aberration diagrams of Numerical Example 1 to Numerical Example 4 of the present invention, respectively. It is. In the figure, S is Sajimir's side and M is Meridional's side. Patent applicant: Canon Co., Ltd. Conli 41 4 Ro5 Place

Claims (1)

[Claims] (1) In order from the object side, a meniscus-shaped lens with positive refractive power with its convex surface facing the object side, a second lens with both concave lens surfaces, and a third lens with both lens surfaces convex, and a negative refractive lens. From the three lens groups of the laminated lens, which is laminated with the i@4 lens, an aperture is provided on the image plane side of the laminated lens, and R1 is the first lens in order from the object side. The radius of curvature of the surface, Di is the first lens thickness and air gap in order from the object side, and Ni and νi are the first lens thickness and air distance in order from the object side.
The refractive index of the glass of the th lens, the Atsube number, and the composite focal length of the entire lens system are 0.25 <
N, -N4< 0.4 0.25<R1/f<0.33 2 <1RaJ/f However, bird f00, 26
＜几、＜0.35 0,07＜D j/f＜0.10.06＜ShiE1＜0.15 20kuν1〈32 10＜shibata-shi4〈30 Featured photographic lens.