JPH03180808A - Small-sized zoom lens - Google Patents

Abstract

PURPOSE:To obtain a compact lens which has a short lens movement distance and excellent image formation performance although its variable power ratio is about 2 by composing a lens system of lenses in two groups and satisfying specific conditions. CONSTITUTION:The lens system consists of the 1st group composed of a positive meniscus lens 1-1, a biconcave lens 1-2, a positive lens 1-3, and a biconvex lens 1-4 in order from the object side and the 2nd lens group composed of a positive meniscus lens 2-1 having its convex surface on the image side, a negative lens 2-2, and a negative meniscus lens 2-3 in order from the object side. Then inequalities I, II, and III are established, where f1 and f2 are the focal lengths of the 1st and 2nd lens groups R1 the radius of curvature of the lens 2-2 on the object side, R2 is radius of curvature on the image side, and fW the focal length of the whole system on a wide-angle end.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a compact zoom lens, and particularly to a zoom lens that has few restrictions on back focus and is suitable for lens-shutter type compact cameras.

(Prior Art) In recent years, lens-shutter compact cameras equipped with zoom lenses have become mainstream.

In this type of zoom lens, -Unlike zoom lenses for eye reflex cameras, there is no need for a long back focus, and a zoom lens with a short overall lens length is desirable, so it is generally a lens with a positive focal length. A zoom lens has been proposed that has a telephoto refractive power arrangement in which the lens group is located at the front and the lens group with a negative focal length is located at the rear (on the film side). This kind of zoom lens was developed by Japanese Patent Application Laid-open No. 57.
-201213 Publication and JP-A-61-159612
2. Description of the Related Art A two-group zoom lens having a front group with a positive focal length and a rear group with a negative focal length is disclosed in Japanese Patent Publication No.

(Problem to be solved by this invention) These zoom lenses adopt a telephoto type refractive power arrangement, and the overall length of the lens at the wide-angle end is short, but the movement of the second lens group during zooming is The distance is long compared to the variable magnification ratio. Therefore, the member for holding and moving the second lens group during zooming must also be made longer in the optical axis direction, and this determines the overall length of the camera in the optical axis direction. Therefore, in order to make the camera compact, it is necessary to reduce the moving distance of the second lens group.

The present invention provides a zoom lens that has a variable magnification ratio of approximately 2x but has a short moving distance of the second lens group during variable magnification, and therefore allows the total length of the camera in the optical axis direction to be shortened, and also provides good results. The present invention aims to provide a zoom lens with excellent image performance.

(Means for Solving the Problems) In order to achieve the above object, the zoom lens of the present invention has the following features:
A first lens group with a positive focal length and a second lens group with a negative focal length.
In a two-group zoom lens that is composed of a lens group and that changes magnification from a short focal length end to a long focal length end by reducing the distance between the first lens group and the second lens group, the first lens group is .

A 1-3 lens consisting of a positive meniscus 1-1 lens, a biconcave 1-2 lens, and 1 or 2 positive lenses.
The second lens group includes a positive meniscus 2-1 with a convex surface facing the image side from the object side.
The lens is composed of a negative 2-2 lens, a negative meniscus 2-3 lens with a convex surface facing the image side, and further includes a first lens.
, the focal lengths of the second lens group are f and f2, the radius of curvature on the object side of the second lens is R, the radius of curvature on the image side is R2, and the focal length of the entire system at the wide-angle end is It is characterized in that it is configured so that the following conditional expression is satisfied when fw.

1.2<fw/fl<1.6■0.8<
lf, I/f1<1゜3 ■R+R -1,33<<-1,0■Rany2 (Function) In this invention, the configuration of the zoom lens is composed of a positive first lens group and a negative second lens group. By using a telephoto two-group zoom lens, the overall lens length, especially at the wide-angle end, can be shortened.

A camera equipped with this can be made into a compact camera when carried.

In this type of zoom lens, since aberrations in the first lens group are magnified by the imaging magnification of the second lens group, it is necessary to sufficiently correct aberrations and differences in the first lens group. In the present invention,
By configuring the first lens group to include a positive meniscus 1-↓ lens, a negative 1-2 lens, and a positive 1-3 lens unit, spherical aberration and axial chromatic aberration can be well corrected. 1-■ The lens has a meniscus shape convex toward the object side to correct extroverted coma flare for incident light with a large angle of view at the wide-angle end.

In this type of zoom lens, the focal length of the first lens group is fl, the focal length of the second lens group is f2, the focal lengths of the entire system at the wide-angle end and the telephoto end are fw and f, respectively. When the back focus is fBW, it is expressed by the following equation.

Similarly, the back focus at the telephoto end is expressed by the following equation, assuming fBT.

Therefore, if the moving distance of the second lens group is Δx2, △X far few becomes.

Since f, , -f are constants determined by specifications, in order to reduce ΔX2, the refractive power must be distributed so that lf and l/f are small. In this way, conditional expression (2) is a condition regarding the moving distance of the second lens, and if the upper limit of equation (2) is exceeded, the moving distance of the second lens group becomes too large, making it difficult to obtain a compact camera. (2) When the lower limit of the formula is exceeded, the refractive power of the second lens group becomes strong, and the distortion at the wide-angle end becomes large.

The conditional expression is a condition regarding the magnification of the first lens group,
If the upper limit of (2) is exceeded, the influence of aberrations generated in the first lens group becomes large, making it difficult to sufficiently compensate for aberrations. Furthermore, machining accuracy becomes stricter, which impairs mass productivity.

On the other hand, if you go below the lower limit, the back focus at the wide-angle end will become too short.

The lens diameter of the second lens group becomes large, and the camera cannot be made compact.

Conditional expression (■) is a condition regarding the shape of the second lens.If the upper limit of the formula (■) is exceeded, the field curvature will be under-corrected, and if it is below the lower limit, the field curvature will be over-corrected, and a good image will not be obtained. I can't do it.

Furthermore, in order to correct aberrations occurring in the first lens group, it is preferable to use aspheric surfaces for the two surfaces of the first lens group to satisfactorily correct spherical aberrations and distortion aberrations. By using an aspherical plastic lens, mass production is improved and costs can be reduced. In order to correct chromatic aberration, it is desirable to satisfy the following conditions, where νP is the average value of the Abbe numbers of the positive lenses in the first lens group, and ν is the average value of the Abbe numbers of the negative lenses.

νp >50 VN <40 (Example) Examples of the zoom lens of the present invention that satisfy each of the above conditions will be shown below. In the first embodiment, the 1st-2nd lens is made of polycarbonate plastic, and the 1st-4th lens and the 2nd-2nd lens are made of polycarbonate plastic.
The first lens and the second lens are made of acrylic plastic. Four out of seven lenses are made of plastic, making it an extremely lightweight and low-cost zoom lens. Aspherical surfaces are used on the third and eighth surfaces to effectively correct spherical aberration and distortion.

In the second and third embodiments, a glass material with a high refractive index is used for the first and second lenses to satisfactorily correct the curvature of field. In these embodiments, the 1-3rd lens and the 1-4th lens are sufficiently spaced to correct distortion at the wide-angle end.

The fourth embodiment is an example in which the first to third lens units are composed of only biconvex single lenses, and a zoom lens having a variable power ratio of about 2 times is realized with a very small number of lenses. In this embodiment, the 1st-2nd lens is made of recarbonate plastic, and the 1st-3rd and 2nd-2% lenses are made of acrylic plastic. Spherical aberrations are well corrected by using aspheric surfaces on the fourth and sixth surfaces.

In the fifth embodiment, in addition to the structure of the fourth embodiment, the 2-1 lens is also an acrylic plastic lens. It has a 6-element structure and uses plastic lenses for 4 of them, making it an extremely lightweight and low-cost 2x zoom lens. In this embodiment, aspherical surfaces are used for the third and sixth surfaces to correct spherical aberration and distortion.

In addition, each symbol in Table 1 is as follows: R is the radius of curvature of each refractive surface, D is the distance between the refractive surfaces, N is the refractive index of the lens material, vd is the Abbe number, f is the focal length of the entire lens system, and ω is the Half angle of view, F
indicates the F number and FB indicates the back focus.

The shape of the aspherical surface is the X axis in the optical axis direction and the Y axis in the perpendicular direction to the optical axis.
Take the axis and take the direction of light travel as positive, K.

When A, , A, , A3, and A4 are aspheric coefficients, they are expressed by the following equation.

First example F=36.0~68.0 FNα=4.0~7.55 ω=31.0' ~ 17.6' Ne * * * Ne d D 15.098 2.20 27.182 2.40 -22.824 2.54 45.577 3.31 42.674 1.66 -102.097 0,40 32.416 2.60 -22,773 variable -50,0233,60 -15,359 (1,80 -19,5231,20 -140,0004,50 -13,5990,80 -35,969 The mark indicates a plastic lens.

F D8 Fe 12.0 13.64 6°49.5 7.15 20°68.0 2.45 39°49.6 57.0 57.0 59.6 57.0 30.0 47.2 1. 77250 1.49200 1.49200 1.49200 1.51823 1.54814 1.511300 8 1 7 Third surface aspheric coefficient K = -0,382875 Al= -2,82694X10-'A2= 3
．． 90242X10-10 8th surface aspheric coefficient K = -1,42758 A1= 3.09399X10-'A2= 1
．． 36932X10-'fw/f, = 1.25
1 f-I/ f1= 1.03 (R work + R2) /
(R1R2) = -1-32 Movement distance of the second lens group during zooming ΔX2ΔX2 = 33.0 Second example F = 35.0 to 70.0 FNα = 3.8 to 7.6
ω=31.7'~17.2' NQ RD N.

1 15.172 2.80 1.5g9132
55.714 1.90 3 -21.993 1.50 1.834004
19.218 1.00 years 61.2 37.2 75.500 -22.015 48.450 -16.727 -296. Lens -17.867 -22.909 -1433.468 -13,680 -40.325 3.00 3.00 2.50 Variable 3.40 0.80 1.00 4.50 1.00 1.61484 1 .56883 1.59270 1.80610 1.83400 51.2 56.3 35.3 40.9 37.2 35, 0 52, 7 70, 0 8 11.75 5, 80 2, 90 F.

7, 72 24, 03 39, 97 4th surface aspheric coefficient K = 2゜A1= 2゜A2= -4゜A3= -5゜43111X10-2 08567×1O-5 96742XIO-” 18703X10-1s A4= − 3,72811X10-2a 5th surface aspheric coefficient = 1.69818 A1= 1.86L12X10-'A2= -5
,20262X10-12A3=-4,79399
X10-”A4=-2,92829X1.O-”f
,/f engineering=1.35 1f,l/f,=0.92(R
□+R,)/(R1-R,)=-1,03ΔX,=3
2.3 Third Example F=35.0~70.0 ω=31.7'~17.2' Na RD 1 1.5,080 2.80 2 54.850 1.90 3 -23.020 1.50 4 18.697 1.00 5 80.387 3.00 6 -23.061 3.00 FN (1 = 3.8 ~ 7.6 - 1.58913 1, .83400 1.61484 ν d 61 .2 37.2 51.2 4, 8, 828 -16.390 -321.378 17.856 -23.637 -1968.706 -13.522 -39j318 2.50 Variable 3.40 0.80 1. 00 4.50 1.00 1.56883 1.59270 11110610 1, EI34.o.

56.3 35.3 40.9 37.2 35,0 52, 7 70, 0 8 12.05 5,90 2゜　90 B 7, 64 24, t.

40, 20 4th surface aspheric coefficient ni=O.

Ai= 2゜A2= -5゜A3= -5゜A4=-3゜0674 8538x 3973X 5099x 6634X 0-s 10-"10-1" o-20 7th surface aspheric coefficient = 2.26221 AI= -5,28352X10-'A2=2.
44987X10-”A3=2.32820X10-”A4=1
．． 70432X10-”fW/f Engineering=1.33 1f,
l/f, = 0.93 (R, +R,)/ (Ryo-R,)
=-1,02ΔX2=32.6 Fourth example F=36.1 to 68. OFNa =4.25~8.0ω
=30.9' ~17.6°* 18.557 173.721 -36.927 23.022 23.956 -18.680 3.80 1.45 1.90 7.61 2.70 Variable d 1 .54072 1.58300 1.49200 47.2 30.0 57.0 * -38,154 16,557 34,529 -299,224 -12,888 -39,049 2,60 0,30 1,30 4 ,80 0,80 1,51633 1,49200 1,77250 64,1 57,0 49,6 36,1 49,5 68,0 6 13,99 7,49 2,70 B 6,62 20, 19 39 .01 4th surface aspherical coefficient = 3.23454 A1 = -5,95554X10-'A2 = -9
,71998X10-"6th surface aspheric coefficient K = -2,24184 Al=-9,66508X10-'A2= 1
．． 25799X10-7fw/f, = 1.24 1f
21/f□=1.02(R,+R2)/(R knee R
2) = -1,25ΔX2 = 32.4 5th Example F = 36.1 ~ 68.1 FNα = 4.0 ~ 7.55 ω = 31.0'' ~ 17.6' 18.474 52.307 -29.365 46.815 23.331 -20.532 -51.994 -16.405 -23.984 -200,000 -13.803 -37.501 2.20 2.40 2.00 6.69 2.37 Variable 3.80 0.80 00 5.00 1.00 1.54072 1.58300 1.49200 1.49200 1.49200 1.78590 47.2 30.0 57.0 57.0 57.0 44.2 * indicates a plastic lens.

D6F11 36.1 14.35 5.9249.5
7.34 20.0168.1 2.20 3
9.53 Third surface aspheric coefficient K = 0.716663 A1 = -1,31375xlO-'A2 = -2
,34505xlO-'6th contour spherical coefficient K = -2,22106 A1= 1.89487xlO-'A2= 1
．． 34177X10''fw/f, = 1.21 I
f,Ll/f,=1.05(R,+R,)/(R,
-R, ) = -1,27ΔX2 = 33.6 (Effects of the Invention) As seen in the examples, the zoom lens of the present invention has the first,
By appropriately arranging the refractive power of the second lens group, the movement distance of the second lens group during zooming is as small as 32 to 33 ai, yet a 2x zoom with a focal length of 35 to 70+ m is achieved. As a result, the length of the entire lens in the optical axis direction can be reduced, and the camera can be made more compact.

In addition, the lens configuration was minimized and optimized, and 2-2
The lens shape has been optimized to effectively correct various political differences, including field curvature.

[Brief explanation of drawings]

1, 3, 5, 7, and 9 are the first, second, and second zoom lenses of the present invention, respectively. FIG. 1 is a cross-sectional view of the third, fourth, and fifth embodiments, and FIG. 1 also shows a method of varying the magnification of the zoom lens according to the present invention. 2nd, 4th, 6th. 8 and 10 are aberration diagrams of the first to fifth embodiments, respectively. In each aberration diagram, (A) is an aberration diagram at the short focus end, (B) is an aberration diagram at the black dot, and (C) is an aberration diagram at the long focal end.

Claims (1)

[Scope of Claims] (1) Consisting of a first lens group with a positive focal length and a second lens group with a negative focal length, the distance between the first lens group and the second lens group can be shortened. In a two-group zoom lens that changes magnification from a focal end to a long focal end, the first
The lens group consists of, from the object side, a positive meniscus 1-1 lens, a biconcave 1-2 lens, and a positive 1-3 lens unit. -3 lens and a biconvex 1-4 lens, and the second lens group includes, in order from the object side, a positive meniscus 2-1 lens with a convex surface facing the image side, a negative 2-1 lens with a convex surface facing the image side, and a negative 1-4 lens. It consists of a 2-2 lens, a 2-3 negative meniscus lens with a convex surface facing the image side, and
The focal lengths of the lens groups are respectively f_1 and f_2, the radius of curvature on the object side of the 2-2 lens is R_1, the radius of curvature on the image side is R_2, and the focal length of the entire system at the wide-angle end is f_
A compact zoom lens characterized in that it is configured to satisfy the following conditional expression when W is W. 1.2<f_W/f_1<1.6 0.8<|f_2|/f_1<1.3 -1.5<(R_1+R_2)/(R_1-R_2)<
-1.0 (2) A small zoom lens according to claim 1, characterized in that the first to third lens units are constituted by a double-convex single lens. (3) The first lens group having a positive focal length and the first lens group having a negative focal length In a two-group zoom lens that is configured by a second lens group having a focal length and that changes magnification from a short focal length end to a long focal length end by shortening the distance between the first lens group and the second lens group,
The lens group consists of, from the object side, a positive meniscus 1-1 lens, a biconcave 1-2 lens, and a positive 1-3 lens unit. -3 lens and a biconvex 1-4 lens, and the second lens group includes, in order from the object side, a positive meniscus 2-1 lens with a convex surface facing the image side, a negative 2-1 lens with a convex surface facing the image side, and a negative 1-4 lens. It consists of a 2-2 lens, a 2-3 negative meniscus lens with a convex surface facing the image side, and
The focal length of each lens group is f_1, and the radius of curvature on the image side is R.
A compact camera 1.2<f_W/f_1< 1.6 0.8<|f_2|/f_1<1.3 -1.33<(R_1+R_2)/(R_1-R_2)
<-1.0 (4) The small-sized camera according to claim 3, wherein the first to third lens units are constituted by a double-convex single lens.