Afocal zoom lens, and microscope having the lens

Details Afocal zoom lens, and microscope having the lens Afocal zoom lens, and microscope having the lens

2000-11-21

2001-11-20

Lester, Evelyn A (Department: 2873)

Optical: systems and elements

Lens

With variable magnification

C359S660000, C359S744000, C359S376000, C359S380000

Reexamination Certificate

active

06320702

ABSTRACT:

This application claims the benefit of Japanese Application No. 11-333154, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the invention
This invention relates to an afocal zoom lens, and more particularly to an afocal zoom lens suited for a microscope.
2. Related Background Art
As afocal zoom lenses used in microscopes or the like, lenses are conventionally known which are disclosed in, e.g., Japanese Patent Publications No. 6-48328 and No. 6-77104.
In recent years, in the field of microscopes, in particular, stereomicroscopes, target specimens to be observed have become rich in variety. Accordingly, it is sought to achieve a zoom ratio much higher than ever. None of conventional afocal zoom lenses, however, have any satisfactory zoom ratio and hence have a problem that any observation well satisfactory to user's demands can not be made.
SUMMARY OF THE INVENTION
The present invention was made taking account of the above problem. Accordingly, an object of the present invention is to provide an afocal zoom lens having a zoom ratio of 14 magnifications or higher and having a good optical performance, and to provide a microscope having such a lens.
To achieve the above object, the present invention provides an afocal zoom lens comprising, in order from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power and a fourth lens group having a negative refractive power;
the second lens group being movable in a fixed direction from the object side to an image side and the third lens group being movable in a fixed direction from the image side to the object side at the time of the zooming of from the low magnification end state to the high magnification end state, and the afocal zoom lens fulfilling the conditions of:
z>
14  (1)
|
f
1
/f
2
|>3.9  (2)
wherein z represents a zoom ratio of the afocal zoom lens; f
1
represents a focal length of the first lens group; and f
2
represents a focal length of the second lens group.
The present invention also provides a microscope comprising an objective lens system, the afocal zoom lens described above and an imaging lens system.


REFERENCES:
patent: 4345822 (1982-08-01), Tachihara
patent: 4666258 (1987-05-01), Kimura
patent: 4752121 (1988-06-01), Kitagishi
patent: 6157495 (2000-12-01), Kawasaki
patent: 59-38651 (1985-09-01), None
patent: 58-228484 (1995-06-01), None
patent: 6-184222-A (1985-09-01), None

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