Modified gaussian lens

Details Modified gaussian lens Modified gaussian lens

1999-09-15

2001-05-15

Epps, Georgia (Department: 2873)

Optical: systems and elements

Lens

Multiple component lenses

Reexamination Certificate

active

06233101

ABSTRACT:

RELATED APPLICATIONS
This application claims the priorities of Japanese Patent Application No. 10-276332 filed on Sep. 30, 1998 and Japanese Patent Application No. 10-291723 filed on Oct. 14, 1998, which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a modified Gaussian lens employed in a monitor camera or the like; and, in particular, to a modified Gaussian lens having a bright F number of about 1.8 and a ratio of focal length to image size of about 4.5.
2. Description of the Prior Art
There has conventionally been known a modified Gaussian lens of a five-group, five-element configuration in which a cemented lens positioned immediately downstream of a stop in a Gaussian lens is constituted by a single lens.
Though such a modified Gaussian lens is advantageous in that the number of lenses is cut down, so that a compactness can be attained, various kinds of aberration such as chromatic aberration are considered to be hard to correct since the lens located immediately downstream of its stop is a single lens. Therefore, the one disclosed in Japanese Unexamined Patent Publication No. 57-2013 defines lens conditions so as to attain performances which are at least as good as those of a Gaussian lens of a six-element configuration.
The prior art disclosed in the above-mentioned publication and the like aim for use as a taking lens of a single-lens reflex camera, and are not intended to be mounted to a monitor camera or the like.
Therefore, such a lens has not satisfied conditions suitable for a relatively telephoto lens mounted to a monitor camera or the like, i.e., an F number of about 1.8 and a ratio of focal length to image size of about 4.5.
SUMMARY OF THE INVENTION
In view of such circumstances, it is an object of the present invention to provide a modified Gaussian lens of a five-group, five-element configuration which satisfies conditions suitable for a relatively telephoto lens mounted to a monitor camera or the like, i.e., an F number of about 1.8 and a ratio of focal length to image size of about 4.5.
The modified Gaussian lens comprising, successively from an object side, meniscus first and second lenses each having a positive refracting power with a convex surface directed onto the object side, a meniscus third lens having a negative refracting power with a concave surface directed onto an image side, a meniscus fourth lens having a negative refracting power with a concave surface directed onto the object side, and a fifth lens made of a biconvex lens, said modified Gaussian lens satisfying the following conditional expression (1):
0.37
<f
1,2
/f<
0.57  (1)
where
f is the focal length of the whole system; and
f
1,2
is the composite focal length of the first and second lenses;
Preferably, the modified Gaussian lens, further satisfying the following conditional expressions (2) and (3):
0.62
<&Sgr;d/f<
1.03  (2)
0.13
<L/f
<0.26  (3)
where
&Sgr;d is the total length of the lens system; and
L is the air space between the third and fourth lenses.
Preferably, the modified Gaussian lens, further satisfying the following conditional expressions (4) to (6) in addition to or without expressions (2) and (3):
22.0<&ngr;
2
−&ngr;
3
<36.0  (4)
6.0<(1/
R
6
+1
/|R
7
|)×
f<
11.2  (5)
−1.72
<R
10
/R
11
<0  (6)
where
&ngr;
i
is the Abbe number of the i-th lens; and
R
i
is the radius of curvature of the i-th surface.
The modified Gaussian lens, further satisfying the following conditional expressions (2) to (6):
0.62
<&Sgr;d/f
<1.03  (2)
0.13
<L/f
<0.26  (3)
22.0<&ngr;
2
−&ngr;
3
<36.0  (4)
6.0<(1
/R
6
+1
/|R
7
|)×
f
<11.2  (5)
−1.72
<R
10
/R
11
<0  (6)
where
&Sgr;d is the total length of the lens system; and
L is the air space between the third and fourth lenses.
&ngr;
i
is the Abbe number of the i-th lens; and
R
i
is the radius of curvature of the i-th surface.


REFERENCES:
patent: 5999324 (1999-12-01), Kohno et al.
patent: 55-163509 (1980-12-01), None
patent: 56-102819 (1981-08-01), None
patent: 57-2013 (1982-01-01), None
patent: 4-177309 (1992-06-01), None

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