JPH02143212A - Zoom lens - Google Patents

Abstract

PURPOSE:To reduce the cost of a zoom lens by using a lens system having a basic lens constitution arranged with a rear tele-converter as the 1st lens group and changing the interval between the 1st and 2nd lenses and moving quantity of the 1st lens group at the time of variable power by keeping the 2nd group lens at the same position. CONSTITUTION:This zoom lens is constituted of, from the object side, the 1st group having positive power and 2nd group having negative power and the interval between both groups is changed at the time of variable power. By inserting a magnifying system having negative power on the rear side of the 1st group having positive power, the range of the zooming focal distance is changed from a wide-angle side to a telephoto side. The negative power of the magnifying system inserted into this zoom lens when a focusing area is formed on the telephoto side is produced by constituting the system from the object side of a positive lens and negative lens. The magnification M, refractive index N of the negative lens, and the radius of curvature R2 of the 2nd convex surface on the object side of the positive lens of the magnifying system satisfy conditions of inequalities I to III, where the f1 represents the focal distance of the 1st group. Therefore, a shift can be established and the cost of the zoom lens can be reduced, because the 2nd group lens can be used commonly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to means for changing the focal length of a zoom lens system for a compact camera, which is shifted to the telephoto side.

[Prior Art] Zoom lenses for compact cameras are often configured with a two-group zoom system consisting of a first group with positive power and a second group with negative power, in order from the object side. The focal range is often 2x zoom, including the wide-angle side of about 35 mm to 70 mm. If you want to obtain a lens system that shifts this to the telephoto side of about 50 mm to 100 mm, you can install a teleconverter on the front side. I had to either add a lens system or change to a completely different zoom lens system.

[Problems to be Solved by the Invention] When shifting the focal range of a zoom lens for a compact camera from wide-angle to telephoto, adding a teleconverter lens system to the front side causes problems in size and image quality. It was not practical.

Additionally, a rear teleconverter is an effective means for shifting the focal range from wide-angle to telephoto.

However, the 21i1' type zoom lens for compact cameras has a short lens back and a large rear lens diameter, so space for a converter becomes an issue.

On the other hand, there was a problem in that changing to a different zoom lens system would be extremely costly and time consuming.

The present invention aims to reduce costs by avoiding changes in all lens systems and by using some lens systems in common while maintaining high performance.

[Means for Solving the Problems] The present invention provides a two-group zoom system consisting of a first group with positive power and a second group with negative power in order from the object side. The first group is a lens system based on a lens configuration with a rear teleconverter with negative power that can extend the focal length of the first group, and the second group is left as is. By changing the movement angle, the resulting focal range is shifted toward telephoto.

[Function] In converting a focal range closer to a wide-angle to a closer to telephoto, the present invention uses the lens configuration of the first group, places a rear converter behind it, and changes the first group. The reason for using this lens configuration is that the aberrations are already settled at the wide-angle stage, and do not deteriorate significantly even when a rear teleconverter is inserted.

Having a negative power magnification system consisting of a positive lens and a negative lens in order from the object side behind the first group lens system is useful for converting the focal range from wide-angle to telephoto. Since a lens system that expands the focal length is required, a rear teleconverter with a negative power having an enlarging effect is disposed behind the first group of a two-group zoom lens, and its lens configuration is stipulated.

Due to cost and compactness issues, the lens configuration is made of two lenses, a positive lens and a negative lens, and the positive lens is placed first. This is to correct the lower rays of the frames so that they do not become under-lit or over-exposed, and this is because it would be bad if the negative lens preceded them.

Condition (2) is that if 1M, which defines the magnification M of this magnification system, is less than the lower limit, the magnification system is useless, and the first group itself becomes large. If M exceeds the upper limit, the magnification will be too strong and the first group will become smaller, but the power of each lens in the first group will become stronger, causing higher-order aberrations and making aberration correction difficult. Become.

Condition (2) defines the refractive index N of the negative lens of the magnifying system. Since the magnifying system has negative power, the Petzval sum tends to increase in the positive direction.Therefore, it is necessary to use high refractive index glass for the negative lens and low refractive index glass for the positive lens to suppress the increase. be.

If N is less than the specified value, the total Petzval sum of the entire system increases in a positive direction, which is not preferable because the sagittal coma increases.

Condition (2) defines the shape of the positive lens of the magnifying system.

By placing a positive lens in the front and directing its second surface convexly toward the image side, excessive spherical aberration and underexposure of the lower rays of the coma that occur in the first group are corrected. Further, the magnifying system has a negative lens behind the positive lens, and the first surface of this negative lens has a shape that cancels out aberrations with respect to the second surface of the positive lens, so that the radius of curvature approximates that of the second surface of the positive lens. Therefore, as the radius of curvature of the second surface of the positive lens becomes stronger, the radius of curvature of the first surface of the negative lens also becomes stronger.

If condition (2) does not meet the lower limit, the radius of curvature of the second surface of the positive lens becomes too strong, and the first surface of the negative lens also becomes strong, increasing higher-order aberrations and making aberration correction difficult. Moreover, when the upper limit is exceeded, the power to correct excessive spherical aberration is insufficient.

[Example] The present invention will be explained below with reference to Examples.

Example 1 shows a wide-angle zoom lens that is the basis of the present invention, and Examples 2 and 3 show zoom lenses converted to telephoto lenses of the invention.

In Examples 2 and 3, the focal range of the wide-angle lens is shifted from 36 mm to 68 mm to a telephoto zoom of 51 mm to 95 mm.

FIG. 1 is a lens configuration diagram showing a zoom lens closer to a wide angle, which is the basis of the present invention, and FIGS. 3 and 5 are lens configuration diagrams showing a zoom lens shifted toward a telephoto side.

Next, numerical examples will be shown.

[Example 1] [Example 2] i ri di l 19.44 2.012 50
．． 55 1.00 3 -16.88 5.83 4 22.30 3.83 5 -15.99 0.20 6 38.80 2.407 -38
．． 80 0.80 -20.80 1.50 36.01 68.01 f=36.01~68.01 ni ν1 1.72342 38.0 1.83400 37j 1.56384 60.8 -20.80 1. 50 1.80420 I645 1.67790 55.5 51, 57 96, 56 d-th 9.60 3.20 1.80420 46.5 f=51.57~96.56 F=4.35~8,15 0M = 1.062 l1 10, 55 F = 3.59 to 6,77 [Example 3] 51, 41 94, 90 d+! 9.60 3.20 f=51.41~94.90 0M=1.141 F=4.25~7.84 [Effects of the Invention] As described above, the present invention provides a two-group zoom lens for use in compact cameras. When shifting the focal range of a lens from wide-angle to telephoto, a lens configuration is used in which a second group with negative power is used in common, and a magnifying system consisting of two positive and negative lenses is placed behind the first group. By replacing the basic lens system with the first group, a shift can be achieved, and cost reduction can be realized by making the lens system of the second group common.

It should be noted that the lens configuration of the wide-angle two-group zoom lens on which the present invention is based is not limited to that shown in Example 1, and it goes without saying that the present invention can be applied to lens systems with other lens configurations. It is also effective in shortening design time.

[Brief explanation of the drawing]

Fig. 1 is a lens configuration diagram showing a zoom lens with a wide-angle orientation, which is the basis of the present invention; Figs. 3 and 5 are lens configuration diagrams showing a zoom lens shifted toward the telephoto side;
6 are aberration diagrams at the wide-angle end and the telephoto end of the zoom lenses shown in FIGS. 1, 3, and 5, respectively. Figure 1 Figure 1 Figure B

Claims (1)

[Claims] A zoom lens consisting of a first group with positive power and a second group with negative power in order from the object side, and which performs magnification by changing the interval between the two groups, wherein the first group with positive power In a zoom lens that inserts a negative power magnifying system behind the lens group to convert the focal length range from wide-angle to telephoto, insert the magnifying system in order from the object side to create a telephoto focal range. , a positive lens, and a negative lens, and the magnification M of the magnification system is 1.04<M<1.18...(1) Also, the refractive index N of the negative lens of the magnification system is N> 1.77...(2) Furthermore, the second surface of the positive lens of the magnifying system is convex toward the image side,
A zoom lens that satisfies the following conditions: 0.6<|R_2/f_1|<0.73 (3), where the radius of curvature is R_2 and the focal length of the first group is f_1.