| 摘要 |
<p>[Problem] To satisfactorily correct the displacement of the point of focus due to temperature variations in an optical system for projection, and to maintain the excellent optical properties of the system, even after correction, without requiring an increase in the size of the device. [Solution] An optical system which is for projection and in which the reduction side is telecentric, wherein a correction lens group (Gp) comprising a portion of the lens groups of the optical system for projection is configured so as to be mobile along the optical axis in order to correct the displacement of the point of focus due to temperature variations. The following conditional expressions (1) and (2) are satisfied. In the expressions: DeltaBf represents the amount the point of focus on the reduction side is moved when the correction lens group is moved fw/100; fw represents the focal length of the entire system; DeltaAt represents the amount the tangential component of the astigmatism of the maximum angle is varied when the correction lens group is moved fw/100; and Imphi represents the maximum effective image circle diameter on the reduction side. (1) 0.5<|DeltaBf/(fw/100)|<5.0 (2) |(DeltaAt×fw)/(DeltaBf×Imphi)|<0.12</p> |
