JPS5832682B2 - Koukakuzu-Murrenskei - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wide-angle zoom lens preceded by a diverging lens group.

Conventionally, zoom lenses that are preceded by this type of diverging lens group have an inverted telephoto power arrangement, which is advantageous when achieving a wide angle at a short focal length, but on the other hand, when zooming,
Fluctuations in spherical aberration and coma aberration were large, and distortion aberration tended to be significantly negative at short focal lengths.

In order to effectively correct all aberrations, it is believed that the focal length of the divergent lens group and the convergent lens group that follows it must be made large to reduce the burden of aberration correction for each component of both groups. was.

Therefore, the overall shape became large and the amount of movement of both groups increased, making it difficult to put it into practical use.

The present invention eliminates these drawbacks, corrects various aberrations in a well-balanced manner while keeping the lens shape small, and in particular, significantly reduces distortion aberration compared to the first embodiment.
The purpose of the present invention is to provide a zoom lens that is further miniaturized by bringing the entrance pupil of a convergent lens group as far forward as possible.

The lens system according to the present invention is composed of two groups, a front group of a diverging lens group and a rear group of a convergent lens group, when viewed from the object side,
Magnification is changed by mechanically moving both groups on the optical axis.

Then, the diverging lens group, which is the front group, is sequentially arranged from the object direction to the first positive lens, the first negative lens, the second negative lens, and the object fJ.
Consisting of four components separated from each other, the first positive meniscus lens is convex to IIJ, and the convergent lens group, which is the rear group, is sequentially connected to the second positive lens from the object direction, and the second positive meniscus lens is convex to the object 1llIJK. It is composed of five components separated from each other: a lens, a third negative lens, a third positive meniscus lens convex toward the image side, and a third positive lens.

These lens components will be described below.

In a zoom lens system in which a diverging lens group precedes the lens, using a positive lens as the frontmost component of the diverging lens group is extremely effective in correcting distortion aberrations.
It is effective to correct high-order chromatic aberrations by using a positive lens with as large an aperture number as possible, and by making the air gap between the second negative lens and the first meniscus lens relatively large. A feature of the diverging lens group is that it plays an important role in balancing aberrations on the short focal length side and the long focal length side.

That is, if the focal length of the first positive lens is flF and the focal length of the entire diverging lens group is fl, it is necessary to satisfy 1.2<f IF/I fll<4.0.

If the lower limit is less than 1.2, the power of the first positive lens becomes too strong and it becomes impossible to correct spherical aberration on the long focal length side.

Moreover, if it is thicker than the upper limit, even if the bending of the first positive lens and the following two negative lenses is taken into account, it will not be possible to obtain the desired good correction of distortion.

Furthermore, if the distance between the second negative lens and the first positive meniscus lens is DF, then satisfying 0.05≦DF/If11≦0.2 means that by making this diverging lens group a thick lens, the shortest focal length can be increased. This makes it possible to simultaneously correct for fluctuations in spherical aberration at the longest focal length and fluctuations in field curvature.

If this lower limit is exceeded, it becomes impossible to simultaneously correct the spherical aberration and field curvature imposed by this effect on the shortest and longest focal lengths, and if the upper limit is exceeded, the divergent group becomes a thick lens. If the lens becomes too large, the principal plane will penetrate deep into the diverging lens group, restricting the range of movement of the converging lens group, and making it impossible to maintain the zoom ratio.

The present invention further promotes miniaturization of the convergent lens group.

In other words, desirable features for the rear group of this type of wide-angle zoom lens are to have an aberration structure that can tolerate the entrance pupil being as far forward as possible, for the Petzval sum to be as positive as possible, and for the overall length to be relatively small compared to its focal length. However, the five-component system of the present invention inherently tends to have a positive Petzval sum compared to the cinna type. The second positive lens, the second positive meniscus lens, does not need to have a very low refractive index and can be configured with a relatively gentle curvature, unlike a negative lens like a sinus type. A large aperture is possible even without three positive lenses in front, and by placing a third positive meniscus lens convex to the image side after the third negative lens, the g
The radius of curvature of the lu can be made thicker, and the oblique light beam can be passed farther from the optical axis than a sonar type.

Therefore, the entrance pupil can be brought forward, and the entire optical system can be made more compact.

Furthermore, by forming each component into a bonded component, correction of higher-order aberrations becomes easier and higher performance is of course promoted.

By using such a convergent lens group as described above, it has become possible to create a wide-angle zoom lens that is compact as a whole, has all types of aberrations comparable to a single focal length lens, and in particular has extremely well corrected distortion aberration fluctuations.

Preferred embodiments according to the present invention will be described below.

Example 1 is one of the basics of this invention.

The specifications of the lens system according to this embodiment are shown below, the shortest focal length state of the lens configuration is shown in FIG. 1, and various aberrations at each focal length state are shown in FIG.

It can be seen that the aberrations are well balanced at all focal lengths.

In Example 2, the third negative lens is a laminated lens, and the refractive index and Atsube number of the positive component are respectively n p s ν
F, and the refractive index and Atsube number of its negative component are n, respectively.
When N x ν, the color change due to spherical aberration at long focal lengths is corrected by using , and the distortion of chromatic aberration caused by this is balanced by making the second positive lens a laminated lens. There is.

The specifications of the lens system according to this example are shown below, the shortest focal length state of the lens configuration is shown in FIG. 2, and various aberrations at each focal length state are shown in FIG.

In each specification table, r is the radius of curvature of each lens surface, d is the center thickness and air gap of each lens, n is the refractive index of each lens, ν
represents the Atsube number of each lens, and the subscript represents the order of each object from 0.

In addition, in the aberration diagram, the solid line in the spherical aberration diagram represents spherical aberration, the dotted line represents the violation of the sine condition, the solid line in the astigmatism diagram represents the sagittal image surface, and the dotted line represents the meridional image surface, respectively. shall be.

Example 1

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a lens showing the shortest focal length state of a lens configuration according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view of a lens showing a shortest focal length state of a lens configuration according to a second embodiment of the present invention. 3 are aberration curve diagrams at each focal length state of the first embodiment of the present invention, and FIG. 4 is an aberration curve diagram at each focal length state of the second embodiment of the present invention.

Claims (1)

[Claims] 1. A zoom lens that is composed of two groups, a front group of a diverging lens group and a rear group of a convergent lens group, in order from the object direction, and that changes magnification by mechanically moving both the groups. The divergent group is composed of four components separated from each other in order from the object direction: a first positive lens, a first negative lens, a second negative lens, and a first positive meniscus lens convex in the object direction. death,
The convergent group includes, in order from the object direction, a second positive lens, a second positive meniscus lens convex in the object direction, a third negative lens,
It consists of a third positive meniscus lens convex to the image fglJ, and five separate parts of the third positive lens, where the focal length of the entire diverging group is fl, and the focal length of the first positive lens is f1Fj A wide-angle zoom lens system that satisfies the following conditions when the distance between the second negative lens and the first positive meniscus lens is set to 1.