Patent ID: 6301057
Filing Date: 2001-10-09
Classification: G02B

Abstract:
A projection lens for forming an image of an object which, in order from its image end to its object end, consists of:(A) a first lens unit having a weak power and comprising at least one aspheric surface;(B) a second lens unit having a positive power and comprising a negative lens element composed of a high dispersion material and a positive lens element composed of a low dispersion material;(C) a third lens unit having a negative power and comprising a positive meniscus lens element and a negative lens element; and(D) an optional field lens which is nearer to the object than to the third lens unit;wherein:f.sub.0 /.vertline.f.sub.1 <0.6; andBFL/f.sub.0 >0.3;where:(i) f.sub.0 is the effective focal length of the combination of the first, second, and third lens units;(ii) f.sub.1 is the effective focal length of the first lens unit; and(iii) BFL is the back focal length of the combination of the first, second, and third lens units for an object located at infinity along the long conjugate side of the projection lens.