Optical: systems and elements – Lens – With field curvature shaping
Reexamination Certificate
1999-03-29
2001-09-25
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
With field curvature shaping
C359S769000
Reexamination Certificate
active
06295166
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a projection lens system for a projection type of television which is applicable to cameras, such as electronic cameras using charge coupled devices or image pickup devices as image recording media and cameras for use with silver films as image recording media.
2. Description of Related Art
Typically, projection lenses for television sets of the type having a liquid crystal screen have a need to employ a telecentric optical system therein in interrelation to a liquid crystal panel, an illumination system and a color composing optical system and/or to have a long back focal distance in order to incorporate the telecentric optical system therein. One of the projection lenses which satisfy these needs is known from, for example, Japanese Unexamined Patent Publication No. 63-81414. This prior art projection lens comprises a less number of lens elements than before and has a back focal distance longer as compared with its focal length, realizing a desired telecentric optical system.
Projection lens having a back focal distance longer as compared with its focal length are confronted with an large-sized external shape. While projection systems using a liquid crystal device throw a picture with distortion enhanced more than a pictures on an ordinary television screen or a printed picture, and hence have to kept distortion as less as possible, the prior art projection lens described in the above mentioned publication is still hard to have sufficiently corrected distortion.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a telecentric projection lens which has a back focal distance necessary to put a supplemental optical system, such as a color composing lens system, therein and is sufficiently corrected in distortion.
The foregoing object of the invention is accomplished by providing a projection lens for a projection type of television system which comprises, in order from the image side or the side of magnification to the object side or the side of reduction, a positive power first lens element having a convex surface on the image side, a positive power second lens element having a convex surface on the image side, a biconcave third lens element, a positive power meniscus fourth lens element having a convex surface on the object side and a positive power fifth lens element having a convex surface on the image side satisfies the following conditions:
0.35<F
12
/F<0.65
−0.30<F
3
/F<−0.13
0.5<F
5
/F<0.85
0.35<BF/F<0.55
where
F
12
is the composite focal length of the first and second lens elements;
F
3
is the focal length of the third lens element;
F
5
is the focal length of the fifth lens element;
F is the focal length of the projection lens; and
BF is the back focal distance of the projection lens.
The projection lens is preferable to satisfy the following condition (V):
1.2<R
7
/R
8
<3.2
where
R
7
is the radius of curvature of the image side surface of the fourth lens element; and
R
8
is the radius of curvature of the object side surface of the fourth lens element.
Further, the projection lens is preferable to shut out an on-axial light bundle on the image side from the object side surface of the first lens element.
The present invention provides a compact projection lens with maintaining well balanced aberrations while having a back focal distance appropriate to incorporate a color composing optical element therein.
REFERENCES:
patent: 3575495 (1971-04-01), Tibbetts
patent: 5257134 (1993-10-01), Sugawara
patent: 5764419 (1998-06-01), Kodama et al.
Fuji Photo Optical Co., Ltd.
Schwartz Jordan M.
Young & Thompson
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