Projection optical system

Abstract

The 1-2nd lens group is divided into three lens groups which move when focusing is performed during the magnification change. Even in a case in which the second optical group is formed of one mirror, it is possible for a primary image to contain appropriate aberration and to hereby reduce aberration of an image which is finally projected onto a screen through the second optical group.

What is claimed is: 
     
         1 . A projection optical system comprising:
 in order from a reduction side,   a first optical group which is formed of a plurality of lenses and has positive power; and   a second optical group which has one reflective surface having a concave non-spherical shape,   wherein the first optical group is formed to include a 1-1st lens group which is fixed when focusing is performed during the magnification change and has positive power, and a 1-2nd lens group which moves when focusing is performed during the magnification change, is formed of a plurality of lenses, and has positive power as a whole, and   wherein the 1-2nd lens group is a lens group which individually moves when focusing is performed during the magnification change, and includes three lens groups of a positive F 1  lens group formed of at least two lenses, F 2  lens group formed of two lenses, and F 3  lens group formed of one negative lens.   
     
     
         2 . The projection optical system according to  claim 1 ,
 wherein the 1-2nd lens group includes one non-spherical lens formed of a resin, as the F 3  lens group disposed on the outermost enlargement side.   
     
     
         3 . The projection optical system according to  claim 1 ,
 wherein the F 2  lens group of the three lens groups configuring the 1-2nd lens group includes a biconvex lens and a biconcave lens in this order from the reduction side.   
     
     
         4 . The projection optical system according to  claim 3 ,
 wherein a positive lens and a negative lens configuring the F 2  lens group form a cemented lens.   
     
     
         5 . The projection optical system according to  claim 1 ,
 wherein, in the 1-2nd lens group, the F 1  lens group is configured of at least two positive lenses, the F 2  lens group is configured of two lenses of a biconvex lens and a biconcave lens in this order from the reduction side, and the F 3  lens group is configured of a resin lens having negative power and having both surfaces subjected to a non-spherical surface process.   
     
     
         6 . The projection optical system according to  claim 1 ,
 wherein the 1-1st lens group has an aperture therein, a positive lens, and at least a negative lens disposed on the enlargement side from the aperture in this order from the reduction side, of which the negative lens has at least one surface subjected to a non-spherical shape process.   
     
     
         7 . The projection optical system according to  claim 1 ,
 wherein the 1-1st lens group includes an aperture therein, at least two sets of cemented lenses of positive lenses and negative lenses disposed on the reduction side from the aperture, and a negative lens having at least one surface subjected to a non-spherical shape process.   
     
     
         8 . The projection optical system according to  claim 7 ,
 wherein the negative lens subjected to a non-spherical shape process, which is disposed on the reduction side from the aperture disposed in the 1-1st lens group is a negative meniscus lens and has at least a non-spherical surface on the concave surface side.   
     
     
         9 . The projection optical system according to  claim 1 ,
 wherein the numerical aperture on the object side is equal to or more than 0.3.   
     
     
         10 . The projection optical system according to  claim 1 ,
 wherein the reduction side is substantially telecentric.   
     
     
         11 . The projection optical system according to  claim 1 ,
 wherein elements configuring the first optical group and the second optical group all have a rotationally symmetric system.   
     
     
         12 . The projection optical system according to  claim 1 ,
 wherein a range of magnification change is equal to or greater than 1.5 times.