PURPOSE: To obtain a large angle of view and the large aperture ratio of a projection lens consisting of three elements in three positive, positive, and negative groups successively from a screen side by introducing aspherical surfaces to the 1st and the 3rd lenses.
CONSTITUTION: A positive plastic lens 1 which has a large-curvature surface facing the screen side, a biconvex positive glass lens 2 which has a large-curvature surface facing the screen side, and a biconcave negative plastic lens 3 which has a large-curvature concave surface facing the screen side are arranged in order from the screen side. Then, both surfaces r1 and r2 of the 1st positive lens 1 and both surfaces of the 3rd negative lens 3 are made into adpherical surfaces having specific aspherical surface coefficients AD, AE, AF, and AF.
NAKAJIMA YASUO
NAGAOKA YOSHITOMI
