JPS61162022A - Reflection/refraction type zoom lens - Google Patents

Abstract

PURPOSE:To make the title device compact by moving the 2nd lens group having negative refractive force and the 3rd lens group having positive refractive force to the image side and the object side respectively to execute power variation and moving the 4th lens group having negative refractive force and the 5th lens group having positive refractive force to reduce the shading of light flux outside the axis. CONSTITUTION:The 3rd positive lens group is moved to the object side in accordance with the increase of a focal distance and at lease one out of the 4th negative lens group and the 5th positive lens group is simultaneously moved to prevent the image surface from movement and to attain power variation. Negative refractive force is applied to the lens group (2nd lens group) arranged in the front of the 3rd lens group. The 2nd lens group can be moved to execute focusing, but it should be fixed at the time of power variation. In addition, the 2nd lens group is separated far from an attached main mirror to strengthen the power. Consequently, the lens diameter of the 2nd lens group is contracted and the whole optical system can be reduced in size.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catadioptric zoom lens having a refractive system and a reflective system, and in particular, a zoom lens that changes magnification by moving a part of the lens group arranged between the reflective system and the refractive system. This invention relates to a high-performance catadioptric zoom lens.

Conventionally, catadioptric zoom lenses having a reflective system and a refractive system are suitable for long focal length zoom lenses, and tend to be used in various photographic lenses. For example, JP-A-48-42
In Publication No. 509, the focal length ranges from 9500 mm to 2000 mm.
A catadioptric zoom lens for telephoto viewing up to mm has been proposed. The zoom lens described above changes magnification by moving two lens groups, the second and third, counting from the secondary mirror. However, in the case of this zoom lens, the lens group following the secondary mirror has positive power, which is disadvantageous for miniaturization.

In a general catadioptric type zoom lens, the light beam reciprocates in the lens system, so the light beam tends to be vignetted, and if an attempt is made to obtain an optical system with a predetermined brightness, the entire optical system tends to become larger. Therefore, in order to reduce vignetting of the light beam, if the refractive power of the lens group for zooming is strengthened and the moving layer is reduced, aberration fluctuations due to zooming will increase, and a more precise mechanical structure will be required. Furthermore, when the refractive power is weakened, the number of moving layers must be increased in order to obtain a predetermined variable power ratio, which tends to increase the size of the lens system.

(Objective) It is an object of the present invention to provide a small catadioptric zoom lens with less high-speed vignetting and less variation in aberrations due to zooming.

In order to achieve this purpose, this catadioptric zoom lens has a first lens group with positive refractive power consisting of a refractive system, a main mirror, and a secondary mirror reflection system according to the traveling direction of the light, a primary mirror of the first lens group, and a secondary mirror. A second lens group with negative refractive power located between the mirror, a third lens group with positive refractive power, a fourth lens group with negative refractive power, and a fifth lens group with positive refractive power are arranged in order, The three lens groups are moved along the optical axis, and at the same time, at least one of the third lens group and the fourth lens group is moved. In the above configuration, as the focal length increases, the positive third lens group is moved toward the object side, and at the same time, at least one of the negative fourth lens group and the positive fifth lens group is moved to prevent image plane movement. The lens group (second lens group) placed in front of the third lens group has negative refractive power.This second lens group performs focusing by moving. However, it is fixed when changing the magnification.

The second lens group was fixed because it receives the convergent light beam from the first lens group and has the effect of bringing it closer to afocal, so if it is moved for zooming, it is likely to experience large fluctuations in aberrations. Also, due to the mechanical structure, it is easy to link other lens groups from the image side of the primary mirror through the aperture of the primary mirror, and if it is far from the primary mirror, the movement mechanism requires complexity and precision.

Note that locating the second lens group far from the primary mirror and increasing its power plays an important role in reducing the lens diameter of the second lens group and downsizing the entire optical system.

In addition, the second lens group is fixed at a negative value so that the light beam warmed by the degree of divergence and convergence enters the third lens group.
Aberration fluctuations due to movement of the lens group are suppressed. Furthermore, the second
It is desirable to make the lens group as small as possible considering its arrangement position, but it is also recommended to make the lens diameters of the third lens group and subsequent lens groups as small as possible and average them to reduce mechanical structural precision and reduce aberration fluctuations. Helps make it smaller.

Furthermore, in the present invention, preferably the third
By satisfying the following conditions, where the focal length of the lens group is f, the moving layer accompanying magnification is m, and the focal length of the entire system is f at the wide-angle end zoom position, and W is the zoom ratio. be.

The reason why multiple lens groups were provided behind the third group was to distribute the refractive power so that the edges of the light beam passing through the lens groups would not be too uneven, and the light beam would pass smoothly with a small diameter. It can be successfully adapted to the unique configuration of a reflective lens included in the lens system.

On the other hand, conditional expressions (1) and (2) appropriately set the refractive power and moving layer of the third lens group at this time, reduce aberration fluctuations during zooming, reduce the size of the entire lens system, and reduce off-axis light flux. This is to reduce vignetting.

If the lower limit of conditional expression (1) is exceeded and the refractive power of the third lens group weakens, the moving layer of the third lens group must be increased in order to obtain a predetermined variable power ratio. This is undesirable because it increases the vignetting of the external light beam.Also, if the refractive power of the third lens group increases beyond the upper limit, the moving layer during zooming will decrease, but the amount of aberration fluctuation will decrease. Conditional expression (2), which makes it difficult to achieve good aberration compensation over the entire magnification range, requires appropriately setting the moving layer and zoom ratio of the third lens group under conditional expression (1). It is a thing,
If the lower limit of conditional expression (2) is exceeded and the moving layer of the third lens group becomes smaller than the zoom ratio, the refractive power of the third lens group must be strengthened, and as a result, aberration fluctuations during zooming become large. It's coming. Furthermore, if the moving layer of the third lens group is increased beyond the upper limit compared to the zoom ratio, vignetting of the light beam will increase, which is not preferable.

In the present invention, when the fourth lens group with negative refractive power is moved during zooming, the following conditions are satisfied: the moving layer of the fourth lens group accompanying zooming is V, and the focal length is frv. It is preferable to let

In addition, when the fifth lens group with positive refractive power is moved during zooming, it is preferable that the moving layer of the fifth lens group accompanying zooming satisfy the following condition: V, where fV is the focal length, and V. .

If the lower limits of conditional expressions (3) and (4) are exceeded and the refractive powers of the fourth and fifth lens groups weaken, the moving layer when performing image plane complementation during zooming This makes it difficult to downsize the zoom lens as a whole. Moreover, if the refractive power of the fourth lens group and the fifth lens group becomes strong beyond the upper limit, aberration fluctuations will increase with zooming, and many higher-order aberrations will occur, which is not preferable.

Note that when both the fourth lens group and the fifth lens group are moved, it is preferable to set them so that all of the above-mentioned conditional expressions are satisfied.

Also, the configuration in which the fourth lens group is negative and the fifth lens group is positive is convenient for making the power of the fifth lens group relatively weak and suppressing aberration fluctuations, but with a focal length of 2000 mm or more, the back focus is likely to be long, so I would rather use 10
This is particularly advantageous for focal lengths of 00 mm or less.

In addition, in order to reduce aberration fluctuations especially during zooming and achieve good aberration compensation over the entire zooming range, the second lens group is configured with a biconcave lens and a biconcave lens with a convex surface toward the object side in order from the object side. The third lens group consists of a cemented lens with a meniscus-like positive refractive power that faces toward the image plane, and the third lens group consists of a biconvex lens, a biconvex lens, and a meniscus-like negative refractive lens with the convex surface facing the image plane. It is composed of three lenses, the fourth lens group is composed of a positive cemented lens and a lens with negative refractive power, and the fifth lens group is composed of a meniscus lens made of a positive lens and a negative lens. It is also possible to separate a part of the second lens group and move it in the optical axis direction to use it for focusing.

As described above, according to the present invention, it is possible to achieve a compact catadioptric zoom lens with less vignetting of off-axis light beams and less variation in aberrations during zooming.

Next, numerical examples of the present invention are shown.
i is the radius of curvature of the i-th lens surface in order from the object side, D
i is the lens thickness and air gap of the first name from the object side, Ni
and νi are numbers corresponding to the refractive index of the glass of the i-th lens in order from the object side.

Note that Di and Nt are shown assuming that the length measured from the left to the right in the direction of light travel is positive.

Numerical Example 1 (Figure 1) f=744.7~913.3 FNo., l:9.9~
11.0 ] ] ] ] Variable spacing Giroux 61.0 Schiff, 64.1 νa=ss, s ν9=55.5 ν1o=30.1 SI1l=63.4 SI12=63.4 ν13=25.4 ν14=25.4 ν15; 50.9 ν16=55.5 Numerical Example 2 (Fig. 2) f=702.9 to 8502 FNo., 1: 9.
0~IO,9R1= 859.223 D 1=
12.00 N 1=1.48749R2=-8
85,29602= 145.28R3= -243,
097D 3 = 12.00 N 2 = 1.516
33R4=-437,86204=-12,00N
3=1.51633I R5=-243,097D
5=-131,28R6=-346,58106=
-5,00N 4 = 1.51633 Variable interval white = 61.0 Schiff = 64.1 νg = 55.5 ν9 = 55.5 ν1o = 3o, t Si11 = 63.4 Si12 = 63.4 ν13 = 25.4 ν14=25.4 ν15=50.9 νts=ss, s 17=25.4 ν18=49.6 Numerical Example 3 (Figure 3) f=826.8~1073.0 FNo, 1 :8.5
~11. OR1= 859.223 D l=
12.00 Nl=1.48749R2=-88
5,29602= 145.28R3±-243,09
7D 3= 12.00 N 2=1.51633
R4 Tomi -437,882D 4= -12,00N 3
-1.51633IR5±-243,09705=-1
31,28R6 Tomi-346-58106=-5,0
0N 4-1.51633R7= 121.015
07=-2,50N 5=1.58913R8=
365.500 08- -2.00R9= -20
8,76409 = 2.00 variable interval white = 61.0 Schiff = 64.1 νB = 55.5 ν9 = 55.5 ν1O = 30.1 11-63.4 12 = 63.4 ν13 = 25. 4 ν14=25.4 ν15=50.9 ν1B=55.5 ν17=25.4 ν18=49.6 Table 1 shows the relationship between numerical examples 1 to 3 and each conditional expression of the present invention.

Table 1 As explained above, magnification is changed by moving the third lens group with positive refractive power to the image side of the second lens group with negative refractive power, and at the same time, the third lens group with positive refractive power is moved toward the object side. By moving at least one lens group of the fourth lens group and the fifth lens group with positive refractive power, vignetting of off-axis light beams is reduced.

This has the effect of making the whole structure more compact.

[Brief explanation of the drawing]

1, 2, and 3 are cross-sectional views of lenses of Examples 1 to 3 of the present invention, respectively. FIG. 4, FIG. 5, and FIG. 6 are diagrams showing various aspects and differences of Examples 1 to 3 of the present invention, respectively. In the figure, (A) is the zoom position at the wide-angle end, (B) is the difference diagram at the zoom position at the telephoto end, ΔS is the sagittal image plane, ΔM is the meridion image plane, Y is the image height, and Z1 to Z3 are the magnification changes. Indicates the direction of movement when Anti-vomiting sweat sine Nama

Claims (1)

[Claims] (1) A first lens group with positive refractive power consisting of a refractive system and a reflection system of main and secondary mirrors according to the traveling direction of light, and between the primary mirror and the secondary mirror of the first lens group. A second lens group with negative refractive power, a third lens group with positive refractive power, a fourth lens group with negative refractive power, and a fifth lens group with positive refractive power are placed in order, and the third lens group is A catadioptric zoom lens characterized by moving along an optical axis and changing magnification by simultaneously moving at least one of a third lens group and a fourth lens group. (2) When the focal length of the third lens group is f_III, the moving layer due to zooming is V_III, the focal length of the entire system at the wide-angle end zoom position is f_W, and the zoom ratio is Z, then 7<f_W/f_III< 13. The catadioptric zoom lens according to claim 1, which satisfies the following condition: 12<f_III/Z<16. (3) When the fourth lens group is moved during zooming, when the moving layer accompanying zooming is V_IV and the focal length is f_IV, 2.5<|f_W/f_IV|<5.0 0.2< A catadioptric zoom lens according to claim 1 or 2, which satisfies the following condition: |f_IV/Z|<7. (4) When moving the fifth lens group during zooming, if the moving layer associated with zooming is V_V and the focal length is f_V, then 0.3<f_W/f_V<3.0 5<|f_V/Z| The catadioptric zoom lens according to claim 1 or 2, wherein the catadioptric zoom lens satisfies the condition <25.