2510332 - February 2009
Proximity of stop to rear aperture in a projection lens makes it difficult to manage stray light entering the projection lens. Also, for this reason, no illumination surfaces should be closer to the device than the rear of the projection lens, as they tend to become sources of stray light entering the projection lens.
Field-lens surface reflections from the illumination path are not controllable by the device state. These reflections can enter the projection lens pupil and deteriorate contrast. Careful modeling of surface reflections with commercially available optical design software is imperative.
It is very difficult to design lens-shift into a non-telecentric design. The numerical aperture of the projection lens has to be oversized by the amount of lens shift desired. This creates low f/# projection optics and flat state light overlap management issues. Also, it increases the size of the lenses, causing a need for more physical separation (offset) of the illumination and projection ray bundles.
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