JPH03172813A - Small-sized zoom lens - Google Patents

Abstract

PURPOSE:To provide the zoom lens which is compact, good in performance and low in cost by constituting the 2nd group of a piece of negative lens having an aspherical face to constitute the zoom lens which executes variable powers by changing the spacing between the positive 1st group and negative 2nd group successively constituted from an object side. CONSTITUTION:The 2nd group of the zoom lens, which is constituted, successively from the object side, of the 1st group having a positive refracting power and the 2nd group having a negative refracting power and executes the variable powers by changing the spacing between the 1st group and the 2nd group, is constituted of one element of the negative lens having the aspherical face. While the aspherical face of the 2nd lens may be formed only on the image side face or may be used on both faces without any optical problems, the aspherical face is provided on the object side face of a large curvature by taking the ease of production into consideration. The generation of astigmatism on the telephoto side from an intermediate focal length is suppressed in this way. In addition, the generation of chromatic aberrations is suppressed by constituting the positive 1st group of >=2 elements of positive lenses and >=1 elements of negative lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a compact zoom lens, and particularly to a low-cost zoom lens with a small number of lenses suitable for lens-shutter cameras and the like.

(Prior Art) In recent years, zoom lenses in compact cameras have become widespread, and multifocal lenses are becoming mainstream instead of bifocal cameras. However, zoom lenses generally have a large number of lenses and are large in size, making it difficult to meet the demands for lower cost and more compact cameras.

On the other hand, a zoom lens disclosed in Japanese Patent Application Laid-open No. 60-48009 is known as a zoom lens with a relatively small zoom ratio and a reduced number of lenses; The number was 5°6, which was dark.

It has the same magnification ratio, and the F number on the wide side is 4 to 4.
．． 5 and brighter lenses are known in Japanese Patent Application Laid-open Nos. 191216/1983, 87119/1987, and 87120/1983, in which the rear group was constructed with two elements. However, in a lens shutter camera with a short back focus, the effective diameter of the rear group inevitably becomes large, so configuring the rear group with multiple lenses inevitably increases the cost significantly.

In addition, in the case where the final group has one negative lens,
-263113, but in this case there are 3 positive, positive, and negative
It is a group zoom, and it is clear that the mechanism is more complicated than a two-group zoom.

(Problems to be Solved by the Invention) An object of the present invention is to provide a compact, high-performance, and low-cost zoom lens suitable for lens shutter cameras and the like, with a relatively small number of lenses.

(Means for Solving the Problem) In order to achieve the above object, in the present invention, a zoom lens is constructed of a first group having a positive refractive power and a second group having a negative refractive power in order from the object side. 1. In a zoom lens that performs magnification by changing the interval between the second lens group, the second group is constituted by one negative lens having an aspherical surface.

Further, in the present invention, it is preferable that the positive first group is constituted by two or more positive lenses and one or more negative lenses to suppress the occurrence of chromatic aberration and to satisfy the following conditions.

40 < ν2 (1
)0.6<r□b+r2m<2.0
(2) ν2: Atsube number r of the second group lens: Half paraxial curvature r2b of the object side surface of the second group lens:
Paraxial radius of curvature of the image side surface of the second group lens f z/ f
w < =0.5 (3) 0.5 < If
,/f,! < 2.0 (4) fl, f
2: Focal length of the first and second group lenses ftv: Focal length of the entire system at the wide-angle end (effect) In a positive/negative two-group zoom, the aperture is usually the positive first lens.
Because it is placed within the lens group, the second lens group, which is farther away from the pupil, has a larger effective diameter, and since the passing position of the ray of light differs greatly between wide-angle and telephoto lenses, off-axis aberrations are likely to occur, and aberrations vary depending on the focal length. It tends to become large. In particular, when the second group is composed of one negative lens as in the present invention, it is difficult to correct aberrations with a spherical lens, so it is effective to use an aspherical lens.

In the present invention, by using an aspheric surface in the second group lens that has a strong negative refractive power off-axis, the occurrence of astigmatism from the intermediate focal length to the telephoto side is suppressed, and the image plane becomes undersized. It also corrects the occurrence of coma aberration at the telephoto end.

Equation (1) relates to the Abbe number of the second group lens, and when it becomes smaller than the lower limit, the difference in axial chromatic aberration between wide-angle and telephoto becomes large, the axial performance deteriorates, and the number decreases at the wide-angle end. Lateral chromatic aberration increases.

Equation (2) relates to the shape of the second group lens, and when the lower limit is exceeded and the meniscus shape becomes strong.

Due to the strong concave surface, the difference in spherical aberration between wide-angle and telephoto becomes large, and when the upper limit is exceeded, the concave shape on the image side becomes strong, resulting in large positive distortion at wide-angle.

Equation (3) relates to the focal length of the second group lens, and when the upper limit is exceeded, the back focus at the short focus end becomes short and the diameter of the second group increases.

Equation (4) relates to the amount of movement of the second lens group during zooming, and is a condition for reducing the amount of movement of the second lens group, which has a large diameter. When the upper limit of equation (4) is exceeded and the power of the second group becomes weaker, the amount of movement of the second group increases, and when the lower limit is exceeded, the back focus becomes shorter and the diameter of the second group becomes larger.

(Example) Examples of the present invention will be shown below. In the table, f is the focal length, F
NQ is the F number, ω is the half angle of view, r is the paraxial radius of curvature, d
is the axial spacing, nd is the refractive index for the d-line, %I, l
is Atsbe's number. The wooden mark represents an aspherical surface, and its shape is defined in an orthogonal coordinate system with the vertex of the surface as the origin and the optical axis direction as the X axis, with the apex curvature as C1, the conical coefficient as K, and the aspherical coefficient as A1 (i=4. 6.8.10) as +A, h” +A,, h” h=JY +Z.

It is expressed as

It should be noted that the aspheric surface of the second group lens may be used only on the image side surface or on both surfaces, but in this example, in consideration of ease of manufacture, the aspheric surface on the object side with a large curvature is used. The surface is aspherical.

[Example 1] f = 36.16-48.83 FNo. 3.8-
5.22ω=60.0~46.62' Surface number r d nal 18.
559 2,500 1.6968 55.548.3
78 -19.916 31.931 57.879 -21.824 105.21 -28.775 Aperture -22,788 2256,7 1,500 4,731 1,133 2,308 0,200 1,500 0, 600 9 1,500 1,7234238,0 1,5891361,2 1,5891361,2 1,5163364,1 d.

23.611 13.901 f 36.16 48.83 Aspheric coefficient 10th surface K = 0.15227 A4 = -1,8922X10-' A, = 1.2860X10-7A, =
-1,5295X10-'〇. = 4.537
7XIO-12 (rzb-r2m)/ (rzb+rz
i) = 1.02 Aspheric coefficient 10th surface K = A4 = A, = A, = A engineering. = -0,61936 -1,7059X10-'-9,1373X10-" 6.9927X 10-" -2,3769X 10-" 2 (r zb-r2a)/ (r 2b4r2.) = 1
．． 50f-/f w” 0.98 1 f
z/ f = 1.24 [Example 3] f = 41.10 to 58.83 2ω = 54.14 to 39.70' Nn 4.5 to 6.5 25.434 53.630 -19. 126 -41.138 78.564 -20.863 2.500 1.500 4.194 4.063 3.000 0.600 n+1 1.6968 1.76182 1.58913 d 55.5 26.5 61.2 f 2/f w”-1,21 [Example 2] f = 41.16 to 58.79 2ω = 54.06 to 39.92 @ f2/f□ = 1.41 FNα 4.5 to 6.5 21.684 82.441 -20.110 52.374 431.83 -22.213 130.28 -29.335 Aperture -20,126 755,86 2,500 1,500 4,000 2,000 2,308 0,200 1,500 0,600 d.

1.500 d 1.6968 55.5 1.72342 1.58913 1.58913 1.487/19 38.0 61.2 61.2 70.2 23.040 13.576 41.16 58.79 Aperture - 19,728 304,66 G 1.500 1.51633 64.1 Aspheric coefficient 6th surface 8th surface 22.470 14.215 41°10 58.83 K = A4 = AG = A, = A1° = K = A4 = A, = A, = A1o= -2,8784 -1,9947X 10-5 4.7366X 10-" -1,4320X 10-10 -1.4905 -2.7517X 10-' -1,2605X 10-' 1.5940x 10-9 -6.0417X 10-" (r zb-rta)/ (r ab+r2m) = 1
．． 14L/ fw= 0.87 l f2/
f□I =i,]4 (Effects of the Invention) As is clear from each embodiment and its aberration curve diagram, the zoom lens of the present invention has one negative lens in the second group.
Despite its minimal configuration, it is bright with an F number of around 4 on the wide-angle side, and aberrations are well corrected, making it a high-performance, low-cost zoom lens.

[Brief explanation of the drawing]

1, 3, and 5 are sectional views of the first, second, and third embodiments, respectively, and FIGS. 2, 4, and 6 are sectional views of the first embodiment, respectively.
, FIG. 7 is an aberration diagram of the second and third embodiments.

Claims (1)

[Claims] In a zoom lens that consists of, in order from the object side, a first group having a positive refractive power and a second group having a negative refractive power, and which performs magnification by changing the distance between the first and second lens groups. , a compact zoom lens characterized in that the second lens group is composed of one lens having an aspherical surface.