Patent ID: 6624952
Filing Date: 2003-09-23
Classification: G02B

Abstract:
A projection optical system that, by using projection light emanating from a light valve illuminated by illumination light, projects an enlarged image of an image displayed on the light valve onto a screen, comprising, from a conjugate enlargement side:a front lens unit having a negative optical power as a whole and including at least one aspherical surface, the front lens unit having a first lens element disposed at a conjugate-enlargement-side end thereof and having a second lens element disposed on a conjugate reduction side of the first lens element, the first and second lens elements both having a negative optical power; optical path turning means, including a reflecting surface, for turning a light path of light emanating from the front lens unit; a rear lens unit having a positive optical power as a whole and including at least one aspherical surface, the rear lens unit including a third lens element made of an anomalous dispersion material and having a positive optical power; and projection light preparing means disposed between the rear lens unit and the light valve and having at least one of a function of separating the illumination light and the projection light and a function of integrating together light of different colors, wherein a center of the light valve is not located on an optical axis of the rear lens unit, and wherein the following conditions are fulfilled: 4831/f<7â€ƒâ€ƒ(2) Vd>75â€ƒâ€ƒ(3) 0.52Ngâˆ’Nf)/(Nfâˆ’Nc)<0.56â€ƒâ€ƒ(4) where&ohgr;represents a maximum angle of view (Â°);Dlrepresents a turning aerial interval (an optical path length, asconverted on an air basis, from a most conjugate-reduction-sidesurface of the front lens unit to a most conjugate-enlargement-sidesurface of the rear lens unit);frepresents a focal length of the entire projection optical system;Vdrepresents an Abbe number of the anomalous dispersion material;Ngrepresents a refractive index of the anomalous dispersion materialfor a g-line;Nfrepresents a refractive index of the anomalous dispersion materialfor a f-line; andNcrepresents a refractive index of the anomalous dispersion materialfor a c-line.