Abstract: A projection system includes a first lens group that does not move when the projection magnification is changed with the aid of the zoom function, and the first lens group includes a correction lens group that is moved in the direction of the optical axis to correct worsened astigmatism. The projection system satisfies the following conditional expressions (1) and (2): |?BF20|<P×FNO×?2??(1) 1.5<|f1/f|??(2) where P represents the pixel pitch in an image displayed by liquid crystal panels, FNO represents the F number of the entire lens system, ?BF represents the amount of movement of the back focus position in a case where the correction lens group is moved by the amount of movement for correction of the aberration that changes when the temperature changes by 20° C., f represents the focal length of the entire lens system, and f1 represents the focal length of the correction lens group.

Abstract: A projection system includes a first lens group that does not move when the projection magnification is changed with the aid of the zoom function, and the first lens group includes a correction lens group that is moved in the direction of the optical axis to correct worsened astigmatism. The projection system satisfies the following conditional expressions (1) and (2): |?BF20|<P×FNO×?2??(1) 1.5<|f1/f|??(2) where P represents the pixel pitch in an image displayed by liquid crystal panels, FNO represents the F number of the entire lens system, ?BF represents the amount of movement of the back focus position in a case where the correction lens group is moved by the amount of movement for correction of the aberration that changes when the temperature changes by 20° C., f represents the focal length of the entire lens system, and f1 represents the focal length of the correction lens group.