Patent ID: 7145729

Claim:
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 f 0 , said lens, in order from the long conjugate side to the short conjugate side, comprising: (I) a first lens unit comprising a plurality of lens elements one of which has an optical surface S 1 which constitutes the short conjugate end of the first lens unit, said plurality of lens elements having a minimum clear aperture CA min/U1 and comprising: (A) a lens element L U1/N1 which: (i) comprises at least one aspheric surface, (ii) comprises a plastic material having a V-value V U1/N1 and a Q-value Q U1/N1 , (iii) has a focal length f U1/N1 , (iv) has a lens element f-number F/# U1/N1 , and (v) has a short conjugate surface which is concave towards the short conjugate side; (B) a lens element L U1/N2 which: (i) comprises at least one aspheric surface, (ii) comprises a plastic material having a V-value V U1/N2 and a Q-value Q U1/N2 , (iii) has a focal length f U1/N2 , and (iv) has a lens element f-number F/# U1/N2 ; and (C) a lens element L U1/P which: (i) comprises a glass material having a Q-value Q U1/P , and (ii) has a focal length f U1/P ; and (II) a second lens unit having a positive power, said lens unit comprising a plurality of lens elements one of which has an optical surface S 2 which constitutes the long conjugate end of the second lens unit, said plurality of lens elements having a maximum clear aperture CA max/U2 and comprising a lens element L U2/P1 which: (i) comprises a glass material have a Q-value Q U2/P1 , and (ii) has a focal length f U2/P1 ; wherein: (a) the first and second lens units are the only lens units of the projection lens; (b) the first lens unit does not include any lens elements which comprise a glass material having a Q-value greater than 50.0; (c) the projection lens has a field of view in the direction of the long conjugate which is greater than or equal to 85 degrees; (d) the projection lens is telecentric on the short conjugate side; (e) the projection lens has an effective back focal length BFL which satisfies the relationship: BFL/f 0 ≧2.0; (f) the projection lens has a mechanical spacing S 1-2 between S 1 and S 2 which satisfies the relationship: S 1-2 /f 0 ≧3.5, where the mechanical spacing is the smaller of the center-to-center distance and the edge-to-edge distance between S 1 and S 2 for an unfolded optical axis; and (g) f U1/N1 , F/# U1/N1 , V U1/N1 , Q U1/N1 , f U1/N2 , F/# U1/N2 , V U1/N2 , Q U1/N2 , f U1/P , Q U1/P , f U2/P1 , Q U2/P1 , C min/U1 , and C max/U2 satisfy the relationships: f U1/N1 <0 F/# U1/N1 ≦1.0; V U1/N1 ≧45; Q U1/N1 ≧100.0; f U1/N2 <0; F/# U1/N2 ≦1.5; V U1/N2 ≧45; Q U1/N2 ≧100.0; f U1/P >0; Q U1/P ≦50.0; f U2/P1 >0; Q U2/P1 ≧35.0; and CA max/U2 /CA min/U1 ≦1.0.