Importance

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Abstract

A projection lens for use with LCD or DMD panels is provided. The lens has three lens units, the first unit having a negative power and at least one plastic lens element having two aspheric surfaces, a second lens unit having a negative power or a weak positive power and at least one color correcting doublet, and a third lens unit having a positive power and an aspheric surface either on a glass element or on a weak plastic element. The projection lens has a back focal length to focal length ratio of at least 3.0, the ratio being achieved by arranging the first, second, and third lens units so that: D.sub.12 /f.sub.0 >1.0, D.sub.23 /f.sub.0 >0.7, and 1.5<(D.sub.12 +D.sub.23 +BFL)/BFL<4.0 where: f.sub.0 is the effective focal length of the combination of the first, second, and third lens units; BFL is the back focal length of the combination of the first, second, and third lens units; D.sub.12 is the distance between the first and second lens units; and D.sub.23 is the distance between the second and third lens units.

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First Claim