Patent ID: 6765731
Filing Date: 2004-07-20
Classification: G02B

Abstract:
A projection lens for forming an enlarged image of a pixelized panel on a screen, said projection lens having an optical axis, a long conjugate side, a short conjugate side, and an effective focal length f0, said lens comprising in order from the long conjugate side to the short conjugate side:(A) a first lens unit having a negative power and comprising a plurality of lens elements, wherein: (i) one of the lens elements LM is a negative lens element of overall meniscus shape which is convex towards the long conjugate side and comprises at least one aspheric surface; and (ii) another of the lens elements has an optical surface S1 which constitutes the short conjugate end of the first lens unit; (B) a reflective surface for folding the projection lens' optical axis; and (C) a second lens unit having a positive power and comprising a plurality of lens elements, wherein: (i) one of the lens elements LA is a positive lens element which comprises at least one aspheric surface; and (ii) another of the lens elements has an optical surface S2 which constitutes the long conjugate end of the second lens unit; wherein: (a) the first and second lens units are the only lens units of the projection lens; (b) the projection lens has a field of view in the direction of the long conjugate which is greater than 82 degrees; (c) the projection lens is telecentric on the short conjugate side; (d) the projection lens has an effective back focal length BFL which satisfies the relationship: BFL/f0>2.0; (e) the projection lens has a mechanical spacing S1-2 between S1 and S2 which satisfies the relationship: â€ƒS1-2/f0>3.5,where the mechanical spacing is the smaller of the center-to-center distance and the edge-to-edge distance between S1 and S2 for an unfolded optical axis; and(f) the projection lens has a lateral color LC in its short conjugate focal plane which satisfies the relationships: LCred-blue<0.0012Â·f0, LCred-green<0.0012f0, and LCblue-green<0.0012f0, where (i) the red-blue and red-green relationships are satisfied over the full field in the short conjugate focal plane, (ii) the blue-green relationship is satisfied over at least 95% of the full field in the short conjugate focal plane, and (iii) the red, green, and blue wavelengths are 0.62 micrometers, 0.55 micrometers, and 0.46 micrometers, respectively.