JPS5843722B2 - Shashin Yokouka Cleanse - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photographic wide-angle lens that has a compact configuration and has extremely well corrected aberrations.

Furthermore, among the means for correcting various aberrations, the means for correcting lateral chromatic aberration is particularly distinctive.

In retrofocus type wide-angle lenses that are conventionally used as wide-angle lenses for photography, high-dispersion glass is used for the positive lens in the front group, and low-dispersion glass is used for the negative lens. The chromatic aberration of magnification has been corrected.

This is based on the idea that if the divergent chromatic dispersion generated in the front group is too large, it will not be possible to compensate for it in the rear group.

On the contrary, the present invention uses low dispersion glass for the first group lens and high dispersion glass for the second group lens, that is, low dispersion glass for the positive lens and high dispersion glass for the negative lens, and as a means for correcting lateral chromatic aberration. The correction concept used in this kind of retrofocus type wide-angle lens uses completely different means, and it is able to correct chromatic aberrations extremely well.

The specific contents of the present invention will be explained in detail below.As shown in Figs. A negative meniscus lens, the fourth group lens is a positive lens, the fifth group lens in the rear group behind the aperture is a negative cemented lens, both the sixth and seventh group lenses are positive meniscus lenses, and It is designed to satisfy the following conditions.

In this Σ, f+234 is the composite focal length of the lenses from the first group to the fourth group, and ν1, ν2, ν3, and ν4 are the Abbe numbers of the lenses from the first group to the fourth group, respectively.

Condition (1) in the above configuration, that is, setting the composite focal length f+234 of the front group from the first group to the fourth group before the aperture to a negative value is one of the features of the present invention, and is a feature of the conventional retrofocus. This is a completely different configuration than most wide-angle lenses of this type, which have positive values.

This contributes to making the lens system more compact; in other words, it prevents the large front lens diameter, which is a drawback of ultra-wide-angle lenses, and is effective in reducing the overall length of the lens system.

At the same time, the fact that the composite focal length f1□34 of the six front groups has a negative value is a condition for making it possible to apply the novel chromatic aberration correction means that is a feature of the present invention. The image will be formed by the rear group at a negative magnification, and if f1□34 is a positive value, the image will be formed at a positive magnification.

However, since the rear group has a positive focal length, the size of the g-line image of the front group must be made larger than the size of the d-line image in order to properly correct lateral chromatic aberration. There will be no.

As described above, since the direction of the image is opposite when the front group has a positive focal length and when it has a negative focal length, the means for correcting chromatic aberration of magnification must also be reversed.

That is, the lens system of the present invention has a lens arrangement having an Abbe number as shown in condition (2), which is a correcting means completely opposite to the conventional correcting means.

If this condition (2) is not met, chromatic aberration of magnification cannot be corrected.

However, when this condition (2) is applied, as in early retrofocus type wide-angle lenses, there is a large distance between the negative lens in the front group and the lens in the rear group, and the positive lens in the first group in the front group Even if it is applied to a type in which the distance from the negative lens of the second group is relatively long, it will cause a large correction error and is not preferable. This can be applied to a device in which the air distance between the second negative lens and the second negative lens is set to a very small value.

Also, the chief ray heights in the first and second groups are the same as those in the third and fourth groups.
Since it is a dog rather than a group, the above conditions (1) and (2) are met.
As shown in FIG. 2, the color correction means can effectively correct the lateral chromatic aberration especially in the periphery of the screen.

Furthermore, it is necessary to select the third and fourth groups as shown in condition (3), and if this condition is not satisfied, the correction of chromatic aberration of magnification will not be satisfactory.

Next, examples of the lens system of the present invention described above will be shown.

Example 1 However, rl...rl5 is the radius of curvature of each surface of the lens, dl...dl4 is the thickness and lens spacing of each lens, and nl...n8 is the radius of curvature of each surface of the lens. refractive index of the lens,
ν1...ν8 is the Abbe number of each lens, f is the focal length of the entire system, fB is the back focus, and f1234 is the combined focal length of the front group, that is, the lenses from the first group to the fourth group.

Example 1 is for the lens system shown in FIG. 1, and the curves showing each aberration situation are as shown in FIG. 3, and Example 2 is for the lens system shown in FIG. 2, and the curves showing each aberration situation are as shown in FIG. is as shown in FIG.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views showing each example of the lens system of the present invention, and FIGS. 3 and 4 are views showing the aberration situation of each of the above-mentioned examples, respectively.

Claims (1)

[Claims] 1. The first group lens is a positive meniscus lens in front of the aperture, and the second and third group lenses are negative meniscus lenses.
The 4th group lens is a positive lens to form the front group, the 5th group lens is a cemented negative meniscus lens behind the aperture, and the 6th and 7th group lenses are positive meniscus lenses. A wide-angle photographic lens characterized by having a lens system consisting of eight elements in seven groups and a rear group, and satisfying the following conditions. However, f1234 is the combined focal length of the front group consisting of the first, second, third, and fourth group lenses, and ν1, ν2, ν3, and ν4 are the first, second, third, and fourth group lenses, respectively. This is the Atsube number of each lens in the 4 groups.