PROJECTION EXPOSURE APPARATUS

摘要

PURPOSE:To enable intermittent variation of a focal length without shifting an image surface vertically, by varying the focal length by providing a transparent plate having different thicknesses between a projection lens and the image surface. CONSTITUTION:A transparent plate 3 having different thicknesses is provided between a lens 1 and an image surface 2 and a focal length is varied by varying the thicknesses. According to this constitution, an optical path is shortened by d-d/n by the transparent plate 3 of a thickness (d) having a refractive index (n) of light, and therefore the focal length can be varied by varying the thickness of the transparent plate 3. Since a focal depth can be varied without shifting the image surface vertically according to this constitution, a projection exposure apparatus enabling attainment of a high throughput can be obtained.