JPH04406A - Zoom lens capable of short-distance photographing - Google Patents

Abstract

PURPOSE:To obtain high power and excellent performance from a short distance to an infinite distance by dividing the 1st group of the lens of three-group constitution into two groups, and moving the 1st group lens forward for focusing while varying the interval between both the groups. CONSTITUTION:The zoom lens system consists of the 1st lens group which has negative refracting power, a 2nd lens group which has position refracting power, and a 3rd lens group which has negative refracting power in order from the object side. Then the 1st lens group consists of the two groups, i.e. a negative biconcave lens group 1-a and a positive lens group 1-b including a positive lens and the 1st lens group is moved forward while the interval between both the groups is increased to perform focusing. Consequently, the distortion of field is prevented to obtain the excellent performance and enable high power variation, and the movement is performed at a constant ratio, so that the mechanism is simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zoom lens capable of close-up photography over the entire zoom range.

(Prior Art) Conventionally, in a zoom lens having a three-group configuration consisting of a negative first lens group, a positive second lens group, and a negative third lens group,
Generally, focusing is performed by extending the first lens group, but there is also
2. Description of the Related Art Rear focus type zoom lenses proposed in Japanese Patent Publication No. 1 and Japanese Unexamined Patent Publication No. 64-74521 are known.

(Problems to be Solved by the Invention) In recent years, zoom lenses are desired to have a close-up photography function, but at the same time, they are also required to have a high zoom ratio and be compact. When trying to obtain a compact zoom lens with a high zoom ratio, the refractive power of each lens group that makes up the zoom lens tends to increase. In the method of focusing by moving the lens alone, the change in aberrations due to focusing becomes large, making it difficult to properly correct aberrations in the range from infinity to close range.

Furthermore, in the method of extending the first lens group, the diameter of the front lens must be increased in order to ensure the amount of peripheral light when the first lens group is extended, which is contrary to compactness. On the other hand, in the rear focus method, the amount of extension varies depending on the focal length even for objects at the same distance, and the focusing mechanism tends to become too complex.

The zoom lens of the present invention is intended to provide a zoom lens that has a high zoom ratio, a simple mechanism, and good performance in photographing from close range to infinity.

(Means for Solving the Problems) In order to achieve the above object, in the zoom lens of the present invention, among the plurality of lens groups constituting the zoom lens, the first lens group is arranged from the object side to the negative 1-a It is composed of a positive 1-b lens group including a lens group and at least a positive lens;
While changing the distance between the a lens group and the 1st-b lens group,
It is characterized by focusing by moving the lens group forward.

For example, as shown in FIG. 1, in order from the object side, it consists of a first lens group with negative refractive power, a second lens group with positive refractive power, and a third lens group with negative refractive power, In a three-group zoom lens, the distance between the first lens group and the second lens group and the distance between the second lens group and the third lens group are monotonically decreased when zooming from the wide-angle end to the telephoto end. Consisting of a negative 1-a lens group consisting of a biconcave lens and a positive 1-b lens group including at least a positive lens from the object side, the distance between the 1-a group and the 1-b lens group is widened. Focusing is performed by moving the first lens group forward.

Furthermore, in order to further simplify the focusing mechanism, the above-mentioned 1-a lens group and 1-
b The amount of change in distance between lens groups. , when the amount of movement of the first lens group is Dl, it is desirable to keep Dab/D□ constant during focusing for objects in all focusing ranges.

(Function) When the refractive power of each lens group is strengthened in order to increase the zoom ratio, the radius of curvature of the lens surface constituting the negative first lens group becomes smaller. In particular, in the first lens group, the radius of curvature of the surface having negative refractive power becomes small. Therefore, when focusing is carried out by extending the first lens group, the off-axis light beam having a large incident angle passing through the first lens group passes through a location away from the optical axis of the first lens group, and the image plane becomes overlapping. This is noticeable at the wide-angle end, where the angle of view is large.

The 1-a lens group in the 1-a lens group is a negative lens group and has a larger refractive power than the entire 1-a lens group, so if focusing is done by extending only the 1-a lens group, the same distance The amount of extension to the object is smaller than the amount of extension of the entire first lens group. However, when focusing is performed by extending only the 1-a lens group, the height of the light beam passing through the 1-a lens group becomes lower, and the height of the light beam passing through the 1-a lens group becomes lower. The divergence effect of the luminous flux is reduced. This results in spherical aberration and an under image surface.

Therefore, when focusing is performed by extending the first lens group while increasing the distance between the 1-a lens group and the 1-b lens group, the above-mentioned effects can cancel each other out, resulting in a change in field curvature. can be prevented. Furthermore, since the 1-a lens group is extended more, the amount of extension ′ can be smaller than when only the first lens group is extended. Also in this case, the amount of extension can be kept constant regardless of the zoom position, so the focusing mechanism becomes simple.

Furthermore, if the 1-b lens group is composed of a negative meniscus lens with a convex surface facing the object side and a positive lens, the refractive power of the negative lens in the 1st lens group can be dispersed, making it easier to correct aberrations. , high magnification is possible. Furthermore, if the concave surface on the image side of the negative lens and the convex surface on the object side of the positive lens are aligned in the 1-b lens group, aberrations due to eccentricity of the 1-a lens group and the 1-b lens group will be reduced. Deterioration is reduced.

The movement of the 1-a lens group and the movement of the 1-b lens group,
It would be ideal to use a cam or the like to move the lens at an arbitrary rate so that aberrations during focusing can be best corrected, but this would tend to make the feeding mechanism complicated and large. Therefore, if the amount of movement of the 1-a lens group and the amount of movement of the 1-b lens group are maintained at a constant ratio, the mechanism can be created by interlocking gears, so the feeding mechanism can be made easier. .

(Example) Examples of the zoom lens of the present invention will be shown below, and the effects of the focusing method of the present invention will be explained.

In each embodiment, the amount of focusing and its aberration diagram for an object with an object-to-image distance of 1 m are shown as an example.

In the first example, D a b / D 1" 0, 5
It is extended so that it becomes, and in the case of 1m, D
a b" 0.

66 degrees, D□=1.31m, the amount of movement of the 1st-a lens group is 1.97 degrees, and the amount of movement of the 1st-b lens group is 1.
．． There will be 31 cabinets. On the other hand, if the first lens group were to be extended as a whole, it would have to be moved by 2 degrees and 4 steps, and the amount of movement in the present invention is 0.4 inches smaller.

In the second embodiment, the beam is extended so that /D1=1.0, and similarly, in the case of 1 m, the beam is extended. =D, =0.7
There are two lenses, and the amount of movement of the 1st-a lens group is 1.44mm, and the amount of movement of the 1st-b lens group is 0°72mm, which is 0.8mm less than extending the 1st lens group as is. .

In addition, each symbol in the table 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, ν is the Abbe number, f is the focal length of the entire lens system, ω is half angle of view, F
indicates the F number.

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.
When the axis is taken, the traveling direction of light is positive, and K, A1, and A2 are aspherical coefficients, it is expressed by the following equation.

1st Example f = 29.06 ~ 78.21 ω = 36.66'' ~ 15.46 @ Plane Na RD F = 3.25 ~ 7.73 1 ν 1 Also, Fig. 2, Fig. 3, and Fig. 4 The figures respectively show (a) an aberration diagram for an object at infinity, (b) an aberration diagram when the first lens is extended as it is, and (c) an aberration diagram for the 1st-a lens group and 1-b lens group of the first embodiment. The aberration diagrams are shown when the first lens group is extended while increasing the distance.
FIG. 8 and FIG. 8 show aberration diagrams for the above cases (a), (b), and (c), respectively, for the second embodiment.

ω=36.69" ~ 15.50' Surface 29.06 48.01 7g, 21 10.08 4.89 0.60 9.83 5.60 3.20 10th valve opening spherical coefficient K = 5 .86073 A 1= 3.01532 X 10-'A, = 2
．． 26674 X 10-' 14th valve opening spherical coefficient K = 1.89614 A 1 = 5.96754
6089 X 10-' Amount of extension for an object at a distance of 1 m (1) In the case of integral extension of the first lens group: 2.4■ (2) In the case of the extension method of the present invention Section 1-a Lens group movement amount: 1 .97m 1st-b lens group movement amount: 1.31m 2nd example f = 29.03 ~ 78.00 F = 3.20 ~ 7.73 19'' -3693,295 F D, D1329.0
3 8.60 10.2748.00
4.48 5.667g, 00
0.60 3.20 10th surface aspheric coefficient
14th valve opening spherical coefficient K = 2.18347
K = 1.21531A1 = 2.91183X10-
'A□=6.68984 x 10-'A! =
2.13663X10"' A2=4.38218
Extension amount for an object of
) In the case of the feeding method of the present invention Section 1-a lens group movement amount: 1.44m 1-b lens group movement amount: 0.72m (Effects of the invention) Figures 3 and 4 and Figures 7 and 7 As is clear from a comparison of FIG. 8, in the zoom lens of the present invention, the change in the image plane due to focusing is small. In particular, the image plane where the angle of view at the wide-angle end is large is shown in Figures 3 (A) and 7 (A).
In contrast, in the case of the present invention, the same shape as the image plane of the aberration diagram for almost infinity is maintained, as shown in Fig. 4 (A) and Fig. 8 (A). There is. Additionally, changes in spherical aberration, especially at the telephoto end, can be reduced, resulting in a zoom lens that has good performance from infinity to close range.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a first embodiment of the zoom lens according to the present invention, and shows the lens locus during focusing as well as during zooming. Figures 2, 3, and 4 are aberration diagrams of the first embodiment, Figure 5 is a sectional view of the second embodiment, and Figures 6, 7, and 8 are aberration diagrams of the second embodiment. It is a diagram. In the aberration diagram, the second
Figures 3 and 6 are for an object at infinity, Figures 3 and 7 are aberration diagrams for an object distance of 1 m when focusing is performed by moving the first lens group as a unit in each example, and Figures 4 and 6 are aberration diagrams for an object distance of 1 m. FIG. 8 shows the focusing method of the zoom lens according to the present invention, and the object distance is the same <1 m. In each aberration diagram, (A) is the aberration diagram at the wide-angle end, (B) is the black dot, and (C) is the aberration diagram at the telephoto end.

Claims (4)

[Claims] (1) Among the multiple lens groups that make up the zoom lens, the first
The lens group is composed of a negative 1-a lens group and a positive 1-b lens group including at least a positive lens from the object side, and the distance between the 1-a lens group and the 1-b lens group is changed. A zoom lens characterized in that focusing is performed by moving a first lens group forward. (2) Consisting of, in order from the object side, the first lens group with negative refractive power, the second lens group with positive refractive power, and the third lens group with negative refractive power, and when changing the magnification from the wide-angle end to the telephoto end , in a three-group zoom lens in which the distance between the first and second lens groups and the distance between the second and third lens groups are monotonically decreased, the first lens group is arranged from the object side with a negative lens consisting of a biconcave lens. 1-a lens group and a positive first lens group including at least a positive lens;
2. The zoom lens according to claim 1, wherein the zoom lens comprises a -b lens group and performs focusing by moving the first lens group forward while widening the distance between the 1-a group and the 1-b lens group. . (3) The zoom lens according to claim 2, wherein the 1-b lens group is composed of a negative meniscus lens with a convex surface facing the object side and a positive lens. (4) In focusing, if the amount of change in the interval between the 1-a lens group and the 1-b lens group is D_■_b, and the amount of movement of the first lens group is D_1, focusing for all objects in the focusing range In D_a_b/D_
2. The zoom lens according to claim 1, wherein the zoom lens is configured to maintain a constant value of 1.