Projection optical system and image projecting apparatus

Abstract

A projection optical system is disclosed. The projection optical system includes a first optical system configured to form a first image conjugated with an object and a second optical system configured to project a second image conjugated with the first image toward a projection surface. At least one of the first optical system and second optical system includes at least one optical element(s) movable relative to the object is provided. An image distance of the projection optical system is changed and a size of the second image is changed, by moving at least one of the optical element(s) relative to the object.

1 - 20 . (canceled) 
     
     
         21 . An image projection apparatus, comprising:
 a lens optical system including a plurality of lenses;   a concave mirror disposed in an outgoing optical path of the lens optical system; and   a housing covering at least the concave mirror and having an aperture that allows light reflected by the concave mirror to pass through,   wherein an end of the aperture is located closer to a light entering side of the lens optical system than a closest lens of the lenses that is closest to the concave mirror.   
     
     
         22 . The image projection apparatus as claimed in  claim 21 , wherein the closest lens of the lenses faces a reflection surface of the concave mirror. 
     
     
         23 . The image projection apparatus as claimed in  claim 22 , wherein another end of the aperture is located between the closest lens and the concave mirror when seen from a projection plane. 
     
     
         24 . An image projection apparatus, comprising:
 a lens optical system including a plurality of lenses;   a concave mirror disposed in an outgoing optical path of the lens optical system; and   a housing covering at least the concave mirror and having an aperture that allows light reflected by the concave mirror to pass through, wherein   a closest lens of the lenses that is closest to the concave mirror faces a reflection surface of the concave mirror; and   an end of the aperture is located closer to a light entering side of the lens optical system than the closest lens of the lenses when seen from a projection plane.