| 主权项 |
1. An optical system for projection that is telecentric on a reduction side,
wherein a correction lens group substantially consisting of a part of lens groups in the optical system for projection is configured to move in the direction of an optical axis to correct a shift in a focal position caused by a change in temperature, and wherein the following conditional formulas (1), (2) and (3) are satisfied:
0.5<|ΔBf/(fw/100)|<5.0 (1);and|(ΔAt×fw)/(ΔBf×Imφ)|<0.12 (2);|D/fpr|<0.50 (3),where
ΔBf: a movement amount of a reduction-side focal position when the correction lens group has been moved by fw/100, fw: a focal length of an entire system, ΔAt: a variation amount of a tangential component of astigmatism at a maximum angle of view when the correction lens group has been moved by fw/100, Imφ: the diameter of a maximum effective image circle on the reduction side, D: a distance on the optical axis from a magnification-side focal position of a combined optical system of the correction lens group through a most reduction-side lens in the entire system to a most magnification-side lens surface in the correction lens group, and fpr: a focal length of the combined optical system of the correction lens group through the most reduction-side lens in the entire system, and wherein ΔBf, fw, ΔAt, D and fpr are values at a wide angle end when the optical system for projection is a variable magnification optical system. |
