| 摘要 |
<p>A projection optical system including a first lens group G1 having positive power; a second lens group G2 having negative power; and a third lens group G3 having positive power wherein the lens elements in each of the lens groups are composed of glass materials selected from the group consisting of fluorite and quartz. Also, the projection optical system satisfies the following condition: <MATH> <MATH> <MATH> where: L: distance between an objective plane and an image plane f: focal length of the entire system f3: focal length of the third lens group G3 f3C: composite focal length of fluorite lens elements which are included in the third lens group G3. <IMAGE></p> |
