Patent ID: 6473244
Filing Date: 2002-10-29
Classification: G02B

Abstract:
A projection lens comprising:a first lens group, a diaphragm, and a second lens group, which are disposed in that order from a long conjugate side to a short conjugate side; wherein the first lens group comprises an aspherical lens disposed at the long conjugate side, and at least one positive lens, so that the first lens group as a whole has a positive refractive power, wherein the second lens group comprises at least one set of combined lenses and an aspherical lens, so that the second lens group as a whole has a positive refractive power, wherein a focusing operation is carried out by moving a gap between predetermined lenses in the first lens group, and conditional expressions (1) and (2) are satisfied: 1.87<BF/FConditional&it;â€ƒ&it;expression&it;â€ƒ&it;(1)0.22<HF2/F2<0.57Conditional&it;â€ƒ&it;expression&it;â€ƒ&it;(2)â€ƒwhere F denotes a focal length of the projection lens, BF denotes a distance in air from a last lens surface of the second lens group to a small conjugate point when a projection magnification is a predetermined value, F2 denotes a focal length of the second lens group, and HF2 denotes a location of a front principal point of the second lens group.