JPS612118A - Method for varying power of zoom lens - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for changing the magnification of a zoom lens, and in particular, a zoom lens having two magnification changing means, a first magnification changer and a second magnification changer, suitable for still cameras, cine cameras, video cameras, etc. This relates to a method of changing magnification.

More specifically, the first magnification change is performed by changing the focal length using a normal method, and the second magnification change is performed by using a different method from the first magnification change to obtain a longer focal length than the first magnification change. This invention relates to a method for changing the magnification of a zoom lens.

Conventionally, various methods of expanding the magnification range of a zoom lens have been proposed. For example, there is a so-called rear converter method in which a rear converter lens group with negative refractive power is inserted between the final lens surface and the image surface of a zoom lens to expand the focal length of all the lenses, and An afocal converter method has been proposed in which the focal length of the gold thread is expanded or decreased by attaching an afocal converter lens group with an infinite focal length.

The rear converter method allows the telephoto ratio to be relatively small, but since it is necessary to properly correct various aberrations in the rear converter lens group alone, the lens structure becomes complicated and large. come. On the other hand, with the afocal converter method, it is relatively easy to make the entire zoom lens system both wide-angle and telephoto, but the lens group tends to become larger because it is attached to the front of the lens. There is. In addition, both converter methods require a converter lens group to be prepared in addition to the zoom lens body, and are therefore not very suitable for instant shooting and portability.

In addition, there is a method of simply changing the magnification ratio of the zoom lens to expand the magnification range. For example, there are methods such as increasing the amount of movement of the lens group for zooming, strengthening the refractive power of the lens group for zooming, or increasing the number of lens groups for zooming. However, with all of these methods, the total length of the lens increases, the amount of various aberrations increases over the entire zooming range, or it becomes difficult to properly correct aberration fluctuations during zooming. There is a tendency to

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for changing the power of a zoom lens that can easily expand the range of power change of the zoom lens.

A further object of the present invention is to provide a method for changing the magnification of a zoom lens, which uses two different magnification changing methods to reduce the size of the entire zoom lens system and expand the magnification changing range, and is excellent in immediate shooting and portability. It is in.

The main features of the zoom lens magnification changing method for achieving the object of the present invention are positive, negative, and positive or negative refractive power in order from the object side. The first lens group has at least five lens groups including a second and third lens group, and the first lens group has a positive refractive power.
It has two lens groups, a -1 lens group and a 1-2 lens group with positive refractive power, and 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. A first magnification change is performed by changing the distance between the lens groups, and at a telephoto end zoom position of the first magnification change, both the 1-1 lens group and the 1-2 lens group have different ratios. The second lens group A, which is made up of the second lens group and at least one lens group located closer to the image plane than the second lens group, is integrally moved to the object side. This means that the zoom range is expanded overall.

As described above, the present invention provides two different methods of variable power, the first variable power and the second variable power, in the same zoom lens system, thereby easily and efficiently changing the power of the zoom lens. increasing range. The zoom range is further expanded from the telephoto end of the first zoom lens to the telephoto side, that is, to the super-telephoto side.

Next, FIG. 1 shows a schematic diagram of an optical system according to an embodiment of the present invention. In the figure, (a) is the wide-angle end of the first variable magnification, (b)
is the telephoto end of the first variable magnification, that is, the wide-angle end of the second variable magnification, (C)
is an optical layout diagram at the telephoto end zoom position of the second variable power.

In the figure, I-1 and I-2 both have positive refractive power.
Lens groups, 1st and 2nd lens groups, ■, I, and N are each negative.

positive and positive refractive power second, third . This is the fourth lens group.

Dotted arrows indicate movement trajectories of each lens group as the magnification changes.

In this example, the first magnification change is performed by moving the second and third lens groups m and m, and the 1-1st lens group and the 1-2nd lens group are moved toward the object side at different ratios. and the second
, 3rd. By moving the lens UYi A, which is composed of the fourth lens group and has a negative refractive power as a whole, toward the object side, the second
The lens was modified to expand the range of magnification and achieve a super telephoto lens.

In this embodiment, the first magnification variable is corrected by non-linearly moving at least one lens group, for example, the third lens group (2), to compensate for fluctuations in the image plane position due to magnification change, as in a normal zoom lens. . In the second magnification change, each lens group is moved linearly using a different magnification method from the first magnification change, so that, for example, only at a predetermined magnification change position, the image plane position matches that during the first magnification change. ing.

This makes it possible to easily and quickly expand the range of magnification while simplifying the mechanism.

During the second magnification change, the 1st-1st lens group and the 1st-2nd lens group are moved at different ratios to efficiently change the magnification, and also to effectively correct aberration fluctuations during the magnification change. are doing.

By performing the second magnification change from the telephoto end zoom position of the first magnification change, the space in the lens system created by the first magnification change can be used efficiently, and the magnification change range can be achieved without increasing the overall length of the lens. We are trying to expand our business.

In this embodiment, the third lens group (2) may have a negative refractive power, and the zoom range can be expanded even if the fourth lens group (2) for image formation is not particularly provided.

In the second magnification change, by nonlinearly moving at least one lens group among the 1-1 lens d, the 1-2 lens group, or the lens group A, the image plane position during the first magnification change is It may be used in the entire magnification range by matching the .

During the second magnification change, the lens group A may be moved integrally with the 1-1st lens group or the 1-2nd lens group. This allows for mechanical simplification.

In this embodiment, when the refractive power of the lens group A is positive, by moving it in the image direction, the range of magnification can be expanded in the same way as described above.

In this embodiment, lens groups A are used as the second, third, . Although the case is shown in which the fourth lens group is composed of six lens groups, the lens group A is the second lens group. The third lens group may be composed of two lens groups. It is preferable to configure the lens group with a small number of lens groups because the moving mechanism becomes simple.

In this embodiment, it is preferable to arrange the fifth lens group having a fixed positive refractive power on the image plane side of the fourth lens group because this makes it easier to reduce the amount of aberration over the entire zoom range.

In this embodiment, the first lens group may be integrally moved toward the object side during the first zooming, and in this way, the range of zooming during the first zooming can be further expanded. .

The object of the present invention can be achieved by satisfying the above conditions, but more preferably, the amount of movement of the 1-1 lens group and the 1-2 lens group during the second magnification change is as follows. It is preferable to set this in order to correct aberrations and shorten the overall length of the lens.

That is, when the refractive power of the 1-1st lens group is stronger than the refractive power of the 1-2nd lens group, the 1-1st lens group is
If the refractive power of the 1-1st lens group is weaker than that of the 1-2nd lens group, the 1st-1st lens group is moved less than the 1-2nd lens group. It means moving a lot.

In particular, in order to shorten the overall lens length while achieving good aberration correction in the second magnification change, it is necessary to
The amount of movement of the -1 lens group and the 1-2nd lens group is set to t1.
t2, the focal length at the telephoto end zoom position of the first variable magnification is f
When T, 0.05fT<ti< 0.25fT @@・・・(
1) 0.7 < t2/ tl < 0.8 ・0
It is preferable to satisfy the condition (2).

If the upper limit of conditional expression (1) is exceeded and the amount of movement of the 1-1 lens IY increases, the zoom range will expand, but the overall length of the lens will become longer, the outer diameter of the lens will also become larger, and the lens barrel structure will become more complicated. Become. Furthermore, the brightness of the entire zoom lens system becomes darker, which is not preferable.

If the lower limit of conditional expression (1) is exceeded and the amount of movement of the first lens group is too small, the expansion of the variable power range will be insufficient, and in order to expand the predetermined variable power range, the number of lenses Bu A will be increased. This is not preferable because the amount of aberration generated increases.

The 1-1st lens group and the 1st lens group exceed the upper limit of conditional expression (2).
- As the amount of movement of the second lens group approaches, it becomes difficult to properly correct aberration fluctuations due to zooming, and if the amount of movement of the first and second lens groups approaches the first -If the amount of movement is smaller than that of the first lens group, it will be difficult to expand the zoom range by a certain amount, and as a result, lens group A will have to be moved further, and aberration fluctuations due to zooming will increase. Undesirable.

Incidentally, the method for changing the magnification of a zoom lens according to the present invention includes a zoom lens that performs the first magnification change by moving the first lens group and the second lens group, and a zoom lens that performs the first magnification change by moving the first lens group and the third lens group. Even if the zoom lens is a zoom lens that changes 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 during the first magnification change, it is suitable. It can be applied to

Next, a numerical example of a zoom lens having the optical arrangement shown in FIG. 1 will be shown. In the numerical example, R4 is the radius of curvature of the th lens surface from the object side, D( is the thickness and air gap of the th lens surface from the object side, and Ni and νt are the radius of curvature of the ith lens surface from the object side, respectively. These are the refractive index and Atsube number of the lens glass.

Numerical Example F-71, 8-246.5 FNO-1: 4.0-8.
02ω-33,6°~10.0°R1-135! Of
D I-2,80N 1=1.80518ν1-25.
4R2-66,70D 2-6.75 N 2-1.6
2230shi2-53.2R3-4072,83D 3-
Variable R4-94, 97D 4-5.00 N 3-1.62
230shi3-53.2R5--1000,00D 5-
1.64 N 4-1.80518ν4-25.4R6
-=-11032,45D 6-Variable R7 helmet 451.
90 D 7-1.50 N 5-1.71300shi5
-53.8R8-39,72D 8-4.20 R9--44,92D 9-1.50 N 6-1.7
1300 Jiro 53.8RIO-44, 93Dlo-5
,40N 7-1.84/)66shi7-23.9R11
--1544,78Dll-variable R12-106,63
D12-5.80 N 8-1.51633 shi 8-64
．． lR13--32, 11D13-1.50 N 9-
1.75520shi9=27.5R14--56,84D
14-Variable R15-(Aperture) D15-0.95 R16-36,48DI6-4.50 N10-1.6
1272ν10-58.7R17-1043, 17D1
7-2.44R18--213, 35D18-2.00
N11-1.80518ν11=25.4R19-5
3730D19-4719 R20--19,81D20-2.00 N12-1.
80610shi12-40.9R21--44,45D2
1-0.20R22-184, 03D22-360N
13-1.5955 Kosi 13-39.2R23--53
,95 In the numerical example, the first magnification change has a focal length f-71,8
~2os, Fsu>bar 4, second variable magnification focal length f-20
5 to 246, and when f-246, the F number is 8.

The amount of movement t1+t2 of the 1-1st lens group and the 1-2nd lens group in the second magnification change is expressed using the above conditional expression as tl-0,185fT, t2/1l-CJ, 756
becomes.

According to the present invention, it is possible to achieve a zoom lens zooming method that can easily and quickly expand the zooming range of the zoom lens.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention, FIG.
FIG. 3 is a lens sectional view and various aberration diagrams of numerical examples of the present invention, respectively. In the figure, I-1, I-2, II, and III. ■Respectively 1-1. Part 1-2. Second. Third. 4th lens group, ΔS is sagittal image plane, ΔM is meridional image plane,
Arrows indicate the direction of movement during zooming.

Claims (1)

Claims: (1) It has at least three lens groups, positive, negative, and first, second, and third lens groups each having positive or negative refractive power in order from the object side, and the first lens group is It has two lens groups, a 1-1 lens group with positive refractive power and a 1-2 lens group with positive refractive power, and the distance between the first lens group and the second lens group and the 1-2 lens group have positive refractive power. The first zooming is performed by changing the distance between the second lens group and the third lens group, and the distance between the first lens group and the first lens group is changed at the telephoto end zoom position of the first zooming. While moving both toward the object side at different ratios, the second
A variable power zoom lens characterized in that a second variable power is performed by integrally moving a lens group A consisting of a lens group and at least one lens group closer to the image plane than the second lens group. Method. (2) The refractive power of the 1-1st lens group is made weaker than the refractive power of the 1-2nd lens group, and at the time of the second magnification change, the 1-1st lens group is replaced by the 1-1st lens group. Claim 1 characterized in that the lens group is moved more than two lens groups.
How to change the magnification of a zoom lens described in section. (3) The lens group A is the 1-1st lens group and the 1st lens group.
- The second magnification change is performed by moving the second lens group at a different ratio.
How to change the magnification of a zoom lens described in section. (4) The zoom lens according to claim 3, characterized in that the focal length of the zoom lens according to the second variable magnification is longer than the focal length at the telephoto end zoom position of the first variable magnification. Variable magnification method. (5) A method for varying the magnification of a zoom lens according to claim 4, characterized in that the lens group A is moved toward the object side. (6) The lens group A has a third lens group with a positive refractive power and a fourth lens group with a positive refractive power disposed on the image plane side of the third lens group, and the first lens group has a fourth lens group with a positive refractive power. The magnification change is performed by moving the second lens group and the third lens group, and the amount of movement of the 1-1st lens group and the 1-2nd lens group when performing the second magnification change is t_1, respectively. , t_2, when the focal length at the telephoto end zoom position of the first variable magnification is f_T, the following conditions are satisfied: 0.05f_T<t_1<0.25f_T 0.7<t_2/t_1<0.8 A method for varying the magnification of a zoom lens according to claim 1, characterized in that: