Objective optical system

Details Objective optical system Objective optical system

1999-03-02

2001-06-26

Epps, Georgia (Department: 2873)

Optical: systems and elements

Lens

With variable magnification

C359S652000, C359S661000, C359S691000, C359S685000, C359S686000, C359S740000, C359S785000, C359S786000, C359S788000, C359S799000, C359S800000, C600S168000, C600S175000, C600S176000

Reexamination Certificate

active

06252723

ABSTRACT:

BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to an objective optical system which has a vari-focal function.
b) Description of the Prior Art
In recent years, there have been demands for endoscopes which permit observation not only of usual images but also of magnified images for precise diagnoses. Furthermore, there have been demands for endoscopes which have non-flexible tips which are short in length and have a small diameter. Accordingly, there have been demands for optical systems for observation of magnified images which have shorter total lengths and smaller outside diameters.
Also in the fields of video cameras and digital cameras, there are demands for lens systems which have shorter total lengths and smaller diameters.
As conventional examples of optical system for observation of magnified images, there are known optical systems disclosed by Japanese Patents Kokoku Publication No. Sho 61-44283, Kokai Publication No. Hei 4-218012 and Kokai Publication No. Hei 6-317744. Each of these conventional examples is a lens system which consists, in order from the object side, of a first lens unit having a positive refractive power, a second lens unit having a negative refractive power and a third lens unit having a positive refractive power, and is configured to perform a vari-focal function by moving the second lens unit along an optical axis.
Since the second lens unit is moved for a long distance for changing a magnification and a diverging light bundle is incident from the second lens unit having the negative refractive power onto a portion of the third lens unit which is remarkably higher than portions of incidence of the other lens units, each of these conventional examples has a defect that it has a large total length and another defect that the third lens unit has a large outside diameter.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide an objective optical system which comprises, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power and a third lens unit having a positive refractive power, performs a vari-focal function by moving the second lens unit along an optical axis, and satisfies the following conditions (1) and (2):
0.1<|1/{f
2
(D
W
−D
T
)}|<2  (1)
1<|(f
W
·f
T
)
½
/f
1
|<2  (2)
Another object of the present invention is to provide an objective optical system which comprises a plurality of lens units and an aperture stop, wherein at least one of the plurality of lens units is moved along an optical axis for performing a vari-focal function and any of the plurality of lens unit satisfies the following condition (3):
0<H
U
/H
S
<0.8  (3)
Still another object of the present invention is to provide an objective optical system which comprises, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power and a third lens unit having a positive refractive power, wherein the second lens unit is moved along an optical axis for performing a vari-focal function, the first lens unit comprises at least one negative lens element and at least one positive lens element, and the third lens unit comprises a negative lens element and at least one positive lens element.
A further object of the present invention is to provide an objective optical system which comprises, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power and a third lens unit having a positive refractive power, wherein the second lens unit is moved along an optical axis for performing a vari-focal function and the optical system comprises a cemented lens component.


REFERENCES:
patent: 4312572 (1982-01-01), Yasmashita et al.
patent: 4-218012 (1992-08-01), None
patent: 6-317744 (1994-11-01), None

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