Patent ID: 6538821
Filing Date: 2003-03-25
Classification: G02B

Abstract:
A projection optical system for projecting an image on a first surface onto a second surface, comprising, in the named order from said first surface side to said second surface side:first lens group of positive refracting power including two or more positive lenses; a second lens group of negative refracting power including two or more negative lenses; a third lens group of positive refracting power including three or more positive lenses; a fourth lens group of negative refracting power including two or more negative lenses; and a fifth lens group of positive refracting power including at least six or more consecutive positive lenses, wherein either one of said fourth lens group and said fifth lens group has one aspherical surface; said fifth lens group has an aperture stop inside thereof; a portion at which a light flux is diverged right before said aperture stop has a first air lens of negative refracting power, a radius of curvature of a lens surface on said first surface side of said first air lens is positive; and a portion at which the light flux is converged at the rear of said aperture stop has a second air lens of negative refracting power, a radius of curvature of a lens surface on said second surface side of said second air lens is negative.