JP3026241B2 - Photographic lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a modified xenotal type photographic lens, and more particularly to a wide angle lens suitable for a lens shutter camera.

[0002]

2. Description of the Related Art A modified xenotar-type photographic lens having a substantially symmetrical arrangement with respect to a stop of six groups and seven lenses is disclosed in Japanese Patent Publication No. 34-379 and Japanese Patent Publication No. 37-13039. The system is known. In a lens of this type, large sagittal coma occurs on two surfaces sandwiching the stop. In order to suppress this occurrence, the radius of curvature of this surface must be increased,
Then, the curvature of the image surface and the astigmatism are degraded. Such problems are more pronounced in wide-angle lenses.
You. Furthermore, these conventional lens systems are designed for a focal plane type camera linked with a distance meter, and only a diaphragm needs to be arranged between the front group and the rear group. The distance between the front group and the rear group was narrow.

[0003]

For this reason, means for improving sagittal coma without deteriorating curvature of field and astigmatism must be taken. In addition, when this type of conventional lens is mounted on a lens shutter camera that has become popular in recent years, the distance between the front group and the rear group of these lenses is too narrow, and it is not possible to arrange a lens shutter unit. If the distance between the front and rear groups is increased to arrange the lens shutter unit, curvature of field and astigmatism will deteriorate, and if it is attempted to correct this, the radius of curvature of the front and rear surfaces sandwiching the aperture will decrease, and especially sagittal There is a problem that the aberration is deteriorated.

The present invention relates to a wide-angle lens having an F number of about 2.
In particular, when the angle of view is 63 ° or more , the occurrence of the above-mentioned sagittal coma is suppressed, and a sufficient space for the lens shutter is secured between the front and rear groups. It is what we are trying to get.

[0005]

In order to achieve the above object, the photographic lens of the present invention has an angle of view of 55 degrees or more , and the first lens unit and the second lens unit have a convex surface in order from the object side. Positive meniscus single lens directed to the side, the third group lens group is a negative meniscus single lens whose convex surface is directed to the object side, the fourth group lens is a negative meniscus single lens whose convex surface is directed to the image side, and the fifth lens group.
The group lens is also a positive meniscus single lens with the convex surface facing the image side, and the sixth group lens is a positive and negative cemented positive lens as a whole and has a configuration of seven groups of six lenses. The power of the air lens formed between the third group lenses is made negative. The sixth lens group may be a positive or negative lens or a negative or positive lens.

Further, in order to secure a sufficient interval for inserting the lens shutter unit between the third lens unit and the fourth lens unit, R: radius of curvature of each lens surface d: interval between each lens surface N : Refractive index of each lens f: Focal length of the whole system P ₂ : Power of air lens formed between the second and third lens groups, that is, P ₂ = (N ₀ −N ₂ ) / R ₄ + (N ₃ -N ₀ ) / R
_{5 where} N ₀ : refractive index of air SF ₂ : shaping factor of air lens formed between second and third lens units, ie SF ₂
= (R ₅ + R ₄ ) / (R ₅ -R ₄ ) The condition of −0.6 / f <P ₂ <−0.23 / f... SF ₂ <8.4. Must meet.

L: the point where the marginal ray of the open F-number intersects the R ₆ surface and R
The distance in the optical axis direction between the intersection with the _seven surfaces N ₆ (N): the refractive index of the negative lens of the sixth group N ₆ (P): the refractive index of the positive lens of the sixth group 0.13f <L <0.19f... N ₆ (N) <N ₆ (P) It is desirable to satisfy the following condition.

[0008]

As described above, in a lens of the type like the lens system of the present invention, large sagittal coma is generated on two surfaces sandwiching the stop. In order to suppress this occurrence, the radius of curvature of this surface must be increased, but this will result in deterioration of curvature of field and astigmatism. Most recent cameras are lens shutter cameras except for single-lens reflex cameras. Assuming that the lens of the present invention is also mounted on a lens shutter camera, a lens shutter unit must be disposed between the front group and the rear group, and this interval must be widened. This causes deterioration of music and astigmatism. To correct this, the radius of curvature of the surface before and after the diaphragm is reduced, and sagittal coma flare is increased.

For this correction, in the lens of the present invention, correction is made by making the power P _{2 of the} air lens formed between the second lens and the third lens negative.

The upper limit of the conditional expression (1) is the upper limit at which the effect of suppressing the increase in sagittal coma aberration while correcting the curvature of field and astigmatism while arranging the lens shutter unit is exceeded. Becomes too small.

However, when this lens is used in a focal plane shutter type camera, it is not necessary to widen the distance between the front and rear groups. This has the effect of increasing the radius of curvature, and can suppress the occurrence of sagittal coma. The lower limit is a limit for preventing overcorrection.

Conditional expression (2) further enhances the effect of expression (1) and suppresses an increase in sagittal coma of the air lens. If the shaping factor of the air lens becomes larger than this, the effect of correcting sagittal coma will be reduced. Disappears.

The conditional expression (3) specifically shows the space where the lens shutter unit enters, the lower limit being the marginal space therefor, and the upper limit being the limit not to cause a decrease in the peripheral light amount ratio.

Conditional expression (4) is for ensuring the convex function of the convex lens at the cemented surface of the sixth lens unit.
In this way, sagittal coma is further reduced.

[0015]

Next, examples of the photographic lens of the present invention will be described. Where f is the focal length of the entire system, R is the radius of curvature of each lens surface,
d indicates a lens thickness or a lens interval, N indicates a refractive index, and V indicates an Abbe number.

Example 1 f = 1 F number = 2.0 Field of view = 63 ° Surface No. R d NV 1 0.7115 0.1118 1.7725 49.6 2 2.214 0.00559 3 0.3474 0.08385 1.7410 52.7 4 0.4585 0.01537 5 0.5847 0.02236 1.71736 29.5 6 0.2554 0.2935 7 -0.2523 0.02516 1.5927 35.3 8 -0.3642 0.00419 9 -0.9007 0.1160 1.7410 52.7 10 -0.3764 0.00559 11 4.005 0.1202 1.7725 49.6 12 -0.7826 0.02795 1.72825 28.5 13 -4.980 P 2 = -0.39 / f SF 2 = 8.27 L = 0.162f

Example 2 f = 1 F number = 2.0 Angle of view = 63 ° Surface No. R d NV 1 0.6742 0.1117 1.7725 49.6 2 2.374 0.00559 3 0.3664 0.08380 1.7440 44.8 4 0.4880 0.01760 5 0.6878 0.02235 1.72825 28.5 6 0.2652 0.2905 7 -0.2522 0.02374 1.5927 35.3 8 -0.3640 0.00559 9 -0.9699 0.1173 1.713 53.9 10 -0.3770 0.00559 11 5.873 0.1201 1.7725 49.6 12 -0.7573 0.02793 1.72825 28.5 13 -3.018 P 2 = -0.46 / f SF 2 = 5.88 L = 0.161f

[0018]

According to the present invention, as is clear from the embodiment and the aberration diagram, a sufficient space for the lens shutter unit is obtained despite the fact that the angle of view is as large as F2 and the angle of view is 63 °. As a result, a photographic lens suitable especially for a lens shutter camera was obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a photographic lens according to a first embodiment of the present invention.

FIG. 2 is an explanatory view

FIG. 3 is a longitudinal aberration diagram of Example 1 of the photographic lens of the present invention.

FIG. 4 is a coma aberration diagram of the first embodiment.

FIG. 5 is a longitudinal aberration diagram of Example 2 of the photographic lens of the present invention.

FIG. 6 is a coma aberration diagram of the second embodiment.

Claims (2)

(57) [Claims] A first lens unit, a second lens unit, a positive meniscus single lens having a convex surface facing the object side, a third lens unit having a negative meniscus single lens having a convex surface facing the object side, The fourth group lens is a negative meniscus single lens with the convex surface facing the image side, the fifth group lens is a positive meniscus single lens with the convex surface facing the image side, and the sixth group lens is a lamination of a positive lens and a negative lens. 6 group 7 which is a positive lens
In sheets having a configuration, angle 55 degrees or more camera lens, characterized in that the power of the air lens negatively formed between the second lens group and the third group lens, R: the lens surface Radius of curvature d: spacing between lens surfaces N: refractive index of each lens f: focal length of the entire system P ₂ : sky formed between the second and third lens units
Power of the lens, ie, P ₂ = (N ₀ -N ₂ ) / R ₄ + (N ₃ -N ₀ ) / R _{5 where} N _{0 is} air
Refractive index SF ₂ : formed between the second group lens and the third group lens
The air lens Shaping Factor i.e. _{SF 2 = (R 5 + R} 4) / (R 5 -R 4) and the time _{-0.6 / f <P 2 <-0.23} / f 5 <SF 2 <8 Wide angle photographic lens characterized by satisfying the condition of 4. Wherein L: open F Distance peripheral rays of the optical axis direction between the point of intersection and the point and the R ₇ side intersecting with R ₆ side of the number N ₆ (N): refraction of the negative lens of the sixth group rate N ₆ (P): claims, characterized in satisfying the condition of the sixth group of 0.13f when the refractive index of the positive lens _{<L <0.19f N 6 (N} ) <N 6 (P) 1 photographic lens