Optical: systems and elements – Lens – With field curvature shaping
Reexamination Certificate
2001-05-08
2002-10-29
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Lens
With field curvature shaping
C359S757000
Reexamination Certificate
active
06473242
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection lens and more particularly to a projection lens with only a few lens elements. The projection lens has only minimal diameters, a short body and a long back focal distance. The aberrations of the projection lens are well corrected.
2. The Prior Art
There are various well-known types of projection lenses for projectors having three spatial light modulators or digital micromirror devices (DMD). In this kind of protector, the light produced falls on three matrices of micro-mirrors. The micro-mirrors are electronically guided and produce images which consist of three color channels. By means of a prism lens or beam concentrator, the images from the three color channels are combined to provide a single full-color image which is reproduced by the projection lens in enlarged form on a screen.
Because the beam concentrator can direct light to the projection lens only below a certain limiting angle, the projection lens has to be nearly telecentric in order to guarantee an optimal light source efficiency. In addition, the projection lens must have a high optical efficiency in order to produce a bright clear image.
In U.S. Pat. No. 5,914,818, such projection lenses are described. These lenses, however, have very large diameters and long assembly cases, and are for that reason heavy and expensive to manufacture.
In U.S. Pat. No. 5,625,495, a telecentric lens is shown. The lens, however, has too short a back-focal distance to use for the application described.
The projection lenses described in U.S. Pat. Nos. 5,969,876, 5,218,480 and 5,969,874 largely fail to meet the required condition of telecentricity.
SUMMARY OF THE INVENTION
In accordance with the invention, a lens is produced with small dimensions, high image quality, a small number of lenses, and of small dimensions. The projection lens is nearly telecentric and has a long back focal distance.
By conforming to certain prescribed lens combinations, the maximum angle of the principal ray to the optical axis on the modulator side of the lens amounts to two degrees or less, with the result that the projection lens is approximately telecentric.
Beginning with the object side of the lens, i.e. the side facing the projection screen, the projection lens comprises a positive lens element L
1
, a negative lens element L
2
, a positive lens element L
3
, or lens element group L
3
Which in turn comprises a negative lens element L
31
and a positive lens element L
32
, followed by a negative lens element L
4
, a positive lens element L
5
, and a positive lens element L
6
.
REFERENCES:
patent: 5099361 (1992-03-01), Yamamoto et al.
patent: 5218480 (1993-06-01), Moskovich
patent: 5539580 (1996-07-01), Kim
patent: 5625495 (1997-04-01), Moskovich
patent: 5914818 (1999-06-01), Tejada et al.
patent: 5969874 (1999-10-01), Moskovich
patent: 5969876 (1999-10-01), Kreitzer et al.
Collard & Roe P.C.
Josef Schneider Optische Werke GmbH
Sugarman Scott J.
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