JPS6239812A - Zoom lens - Google Patents

Abstract

PURPOSE:To correct satisfactorily various aberrations by providing an optical system which has the first group - the third group having positive, negative and positive refractive powers in order from an object side, and executes a variable power by changing a mutual interval of the first group and the second group, and making said optical system satisfy a prescribed condition. CONSTITUTION:The titled lens is constituted of the first group lens 1 having a positive refractive power, the second group lens 2 having a negative refractive power, and the third group lens 3 in order from an object side. In this state, a variable power extending from a wide-angle side to a telephone side is executed by narrowing a mutual interval of the first group lens 1 and the second group lens 2, and moving them to the object side. This first group lens 1 consists of a front group lens 1a having a negative refractive power PSIa, and a rear group lens 1b having a positive refractive power PSIb in order from the object side, and when a refractive power of the whole first group lens 1 is denoted as PSI0, an inequality I and an inequality II are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a compact zoom lens with a small back focus suitable for, for example, a lens-shutter type camera.

[Conventional technology]

Most conventional zoom lenses for still cameras are aimed at single-lens reflex cameras and are designed with a certain degree of bank focus in order to provide the necessary space for the quick return mirror to operate.

For example, the device described in Japanese Patent Application Laid-Open No. 5111-111013 is extremely compact for an eye reflex camera, but its total length exceeds 100 mm even at the shortest focal length, making it suitable for lens-shutter cameras. If used for this purpose, the portability, which is a feature of lens-based cameras, will be significantly hindered.

From this point of view, several zoom lenses have been proposed for lens-shutter type cameras, as described in, for example, Japanese Patent Laid-Open No. 57-201213 and Japanese Patent Laid-Open No. 58-184916.

[Problem that the invention seeks to solve]

However, the zoom lens described in the above-mentioned Japanese Patent Application Laid-Open No. 57-201213 has a focal length variable range of 40
mm to 60 mm, and consists of a first group lens with positive power and a second group lens with negative power arranged in order from the object side.The lens distance between the two groups is changed to change the magnification, and the total length at the wide-angle end is is the same as the focal length, making it highly portable. However, the variable power ratio is as small as 1.5 times, and the performance is also insufficient.

Furthermore, the zoom lens disclosed in Japanese Patent Application Laid-Open No. 513-184916 has a variable focal length range of 40 mm to 58 m.
m, a first group lens with a positive power, a second group lens with a positive power, and a third group lens with a negative power are arranged in order from the object side, and the magnification is changed without mutually moving the three groups, The overall length at the wide-angle end is 6Q, 4mm, which is compact and has satisfactory performance. However, the outer diameter of the third group lens reaches about the diagonal line of the film, and it moves by 26 mm during zooming, so a space for this movement is required on the camera side. Furthermore, at the wide-angle end, the bank focus becomes extremely short at 1.16mm.
You will be very close to the film surface. therefore,
It becomes difficult to secure a space for arranging the film feeding member1, and it becomes necessary to process the lens into a rectangular shape. Furthermore, since the final surface of the lens is very close to the image forming surface, the influence of dust adhering to that surface cannot be ignored.

The present invention has been made in view of the above-mentioned drawbacks of the prior art.The present invention shortens the overall length to improve portability, secures bank focus to the extent that film feeding members can be placed, and It is an object of the present invention to provide a zoom lens that can obtain a variable power ratio of nearly 2 times.

[Means for solving problems]

In order to achieve the above object, the present invention basically consists of a first group lens 1 having a positive power, a second group lens 2 having a negative power, and a positive power The first lens group 1 and the second group lens 3 are disposed when changing the magnification from the wide-angle side shown in FIG. 1(a) to the telephoto side shown in FIG. 1(b). These are moved toward the object side while narrowing the distance between them and 2. Note that the reference numeral 4 in FIG. 1 indicates an image forming surface (film surface).

In the zoom lens configured in this way, the third group lens 3 is given positive refractive power, so the refractive power of the second group lens 2 can be strengthened without making the refractive power of the first group lens 1 excessive. Therefore, it is possible to increase the variable power ratio. Further, by using the imaging magnification of the third group lens 3 in a positive range, a telephoto type refractive power arrangement is always achieved during zooming, which is advantageous in shortening the overall length.

Furthermore, the third group lens 3 is configured to perform different aberration correction actions depending on the zoom position, so that astigmatism and distortion can be particularly well corrected over the entire range of zooming.

In a preferred embodiment of the present invention, the first lens group 1 is configured by arranging, in order from the object side, a front lens group with negative refractive power and a rear lens group with positive refractive power. With this configuration, the rear principal point of the first group lens 1 is closer to the image side, so the movement range of the second group lens 2 for variable magnification can be increased, which is useful for achieving high variable magnification. It will be advantageous. especially,
Between the refractive power ψb of the entire first group lens l, the refractive power ψ1 of the front group lens, and the refractive power ψ of the rear group lens, ψ -0,5<-<0...fl) ψO ψb 1 < - < 1. 5...(2) If the relationship ψO is satisfied, the magnification ratio will be increased.''2 is convenient. Note that if the lower limit of conditional expression (11) and the upper limit of conditional expression (2) above are exceeded, the rear principal point of the first group lens 1 will be too close to the image side and the overall length will become long, impairing compactness. Furthermore, if the upper limit of conditional expression (1) and the lower limit of conditional expression (2) are exceeded, the rear principal point of the first group lens 1 will be too close to the object side and the movement space of the second group lens 2 will be Therefore, in order to achieve a high zoom ratio, the refractive power of the second group lens 2 must be excessively strengthened, making it difficult to correct aberrations during zooming.

Examples of the present invention will be described below.

〔Example〕

FIGS. 2 to 13 show an embodiment in which the lens 1 disposed on the object side has a two-group configuration of a front group 1a and a rear group 1b, together with aberration characteristics at three zooming positions. In addition, in the spherical aberration diagram, the solid line shows the aberration due to the d-line, the dashed line shows the aberration due to the g-line, and the broken line shows the amount of violation of the sine condition. In the astigmatism chart, the solid line shows the aberration in the sagittal plane, and the broken line shows the aberration It shows aberration within the meridional plane.

In each of these examples, the variable range of the focal length f is 36.0 mm to 68.0 mm, and the variable range of the F number is 2.88 to 5.44. For each example,
If the radius of curvature of the i-th surface counting from the object side is R1, the axis-1 distance from the next surface is , the refractive index of the d-line is N8, and the axis number is ν8, then Fig. 2, The data of the first to third embodiments shown in FIGS. 4 and 6 are as follows.

"First Example" t RI Di Nt variable surface spacing D11 and 7, the focal length r is 36.0 mm,
50. 0mm, 68. At 0 mm, it is as follows.

f -36.0 mm 50.0 mm 68.
0 mm Also, the ratio of the refractive power ψ8 of the front group lens 1a and the refractive power ψ of the rear group lens 1b to the refractive power ψb of the entire first group lens 1 is ψ8 -10. 077 ψb ψb -1.05 ψ0, the hack focus f is 7.0.

“Second Example” i Rt D, N,
ν.

The surface distances D1° and DI6 that are changed are as follows: focal length f is 36.0 mm, 50.0 mm. 0mm, 68. At 0 mm, it is as follows.

f = 36.0 mm 50.0 mm 68.
0 mm Also, the ratio of the refractive power ψ of the front group lens 1a and the refractive power ψ of the rear group lens 1b to the refractive power ψb of the entire first group lens I is ψb −−10. 124 ψb ψb −□=1.094 ψO, and the bank focus fb is 7.0.

“Third Example” I Rr D = N i
ν.

The variable interplanar distances D1° and Dt6 are determined when the focal length f is 36. On+m, 50. 01111% 68.
At 011111, it becomes as follows.

f =36.0++++++ 50. Oohm
68. O+am Also, the refractive power ψb of the entire first group lens 1
The ratio of the refractive power ψ of the front group lens 1a and the refractive power ψ1 of the rear group lens 1b to .

In the first embodiment described above, spherical aberration is favorably corrected by the air lens having negative power between the first lens 5 and the second lens 6 included in the first lens group l. Note that it is also possible to make the distance between the first lens 5 and the second lens 6 variable, so that only the spherical aberration can be increased without affecting other aberrations, and a soft focus effect can be obtained. .

The second embodiment is a combination of the second lens 7 and the second lens 8 in consideration of image deterioration due to spacing errors and eccentricity, and the third embodiment is a combination of the second lens 7 and the second lens 8 in order to reduce costs. The first lens 7 and the second lens 8 in the example are constructed as one single lens 9, and the final lens lO of the first lens group 1 is separated to correct spherical aberration.

4. shown in FIGS. 8 and 10. The fifth embodiment shows an example in which an aspherical surface is introduced. These aspherical shapes are represented by . In the above equation, ΔZ is the displacement Y from the apex of the aspherical surface, R1 is the height from the optical axis, R1 is the conic constant A for the paraxial radius of curvature, and is the first-order aspherical coefficient.

4th. The data of the fifth example is as follows.

In addition, regarding the radius of curvature R, the surface marked with "*" is an aspheric surface.

"Fourth Example" t RL Dt N+surface number i=6.
For the aspherical coefficients of 13, the values of A, , and A6 are as follows.

k A a A
b Also, the surface spacings D1° and D14 that are changed are when the focal length f is 36.0 mm, 50.0 mm, and 68.0 mm.
, it becomes as follows.

f = 36.0 mm 50.0 mm 68.
0 mm Also, the ratio of the refractive power ψ of the front group lens 1a and the refractive power ψ of the rear group lens 1b to the refractive power ψb of the entire first group lens 1 is as follows: ψb −-=−0,268 ψb ψ5 □=1 At .300 ψb, the puck focus f is 7.36.

“Fifth Example” i RI DM N.

Aspheric coefficient k at surface number i=6.10.11.

The values of A4, Ah, and As are as follows.

i'k Aa Ah As
Further, the variable interplanar distances D8 and DI2 are such that the focal length f is 36. 0mm550. 0mm568. OL
In Ilm, it becomes as follows.

f=36.0mm 50.0mm
68. Onm, the refractive power ψ of the entire first group lens 1
The ratio of the refractive power ψ8 of the front group lens 1a and the refractive power ψ of the rear group lens 1b to b is ψb □ −0,361 ψb ψb 1−=1.385 ψb, and the hack focus f is 7.0. be.

In the fourth embodiment described above, instead of correcting spherical aberration by an air lens with negative power between the first lens and the second lens in the first embodiment, the rear surface of the third lens 12 is By making it an aspheric surface, spherical aberration is well corrected. Furthermore, by making the concave lens 13 of the second group lens 2 aspherical, the number of concave lenses used can be reduced, the axial thickness of the second group lens 2 can be reduced, and the movement space of the second group lens 2 can be increased. I have to. This makes it possible to shorten the overall length while weakening the power of each group. Further, in the fifth embodiment, the convex lens 14 of the second lens group 2 is also provided with an aspherical surface to improve performance.

In the first to fifth embodiments described so far, the diaphragm 20 is installed inside the first lens group 1, so the entire diaphragm mechanism must be moved during focusing. In this regard, in the sixth embodiment described later, by providing an aperture between the first lens group 1 and the second lens group 2, focusing can be performed by moving only the front lens group. . For this reason, there is an advantage that the driving force can be reduced, especially when focusing is performed using an autofocus mechanism.

“Sixth Example” i RI D5 N.

1 24.083 2.68 1.58144
40.9 The surface spacing to be varied and DI'l are:
Focal length f is 36.0mm, 50.0mm, 68.0m
In m, it becomes as follows.

f =36.0mm50.0mm 68.0m+
n Also, the ratio of the refractive power ψ of the front group lens 1a and the refractive power ψ of the rear group lens 1b to the refractive power ψb of the entire first group lens 1 is: □ = -0,162 ψO ψゎ1□ -1 , 109 ψb and the bank focus f is 6.5.

In the first to sixth embodiments described above, the third lens group 3 is fixed relative to the film surface, but it can be moved in response to zooming to an extent that it does not interfere with the film feeding mechanism. By doing so, it is also possible to further reduce aberration fluctuations during zooming.

〔Effect of the invention〕

As explained above, according to the zoom lens of the present invention, positive, negative, and positive power distribution is performed in order from the object side in a lens system composed of three groups, and the first group lens and the second group lens are By moving these toward the object side while narrowing the distance between them, the magnification is changed from wide-angle to telephoto. As a result, compared to conventional zoom lenses proposed for lens-shutter cameras, it is possible to obtain a zoom lens with a shorter overall length and a higher magnification ratio. In addition, bank focus can be secured to a certain extent, and the film does not get too close to the film surface, so it is very convenient to incorporate it into a camera.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the basic configuration of a zoom lens according to the present invention. FIG. 2 is a sectional view showing a first embodiment of the present invention. FIG. 3 is an aberration diagram of the first embodiment. FIG. 4 is a sectional view showing a second embodiment of the present invention. FIG. 5 is an aberration diagram of the second embodiment. FIG. 6 is a sectional view showing a third embodiment of the present invention. FIG. 7 is an aberration diagram of the third embodiment. FIG. 8 is a sectional view showing a fourth embodiment of the present invention. FIG. 9 is an aberration diagram of the fourth embodiment. FIG. 10 is a sectional view showing a fifth embodiment of the present invention. FIG. 11 is an aberration diagram of the fifth embodiment. FIG. 12 is a sectional view showing a sixth embodiment of the present invention. FIG. 13 is an aberration diagram of the sixth embodiment. 1... 1st group lens 1a... Front group lens 1b... Rear group lens 2... 2nd group lens 3... 3rd group lens 4... Image forming surface (film surface) 20... Aperture. (c) f: 68mm Positive 5E% Mulberry 4,000 (c) f = 68mm (C) f = 68mm (c) f-”68mm J-seeking aberration 1j-steep aberration Distortion aberration positive lame; 7 die Il (C) f”68mm

Claims (3)

[Claims] (1) In order from the object side, a first group lens having a positive refractive power, a second group lens having a negative refractive power, and a third group lens having a positive refractive power are arranged, and the first group lens and A zoom lens characterized in that magnification is changed from a wide-angle side to a telephoto side by moving the second group lens toward the object side while narrowing the mutual distance between the second group lens and the second group lens. (2) The zoom lens according to claim 1, wherein the third group lens is always used at a positive imaging magnification during zooming. (3) The first group lens consists of, in order from the object side, a front group lens having a negative refractive power ψ_a and a rear group lens having a positive refractive power ψ_b, and the refractive power of the entire first group lens is The zoom lens according to claim 1, characterized in that, when ψ_0, -0.5<ψ_a/ψ_0<0 1<ψ_b/ψ_0<1.5.