| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an illumination optical device capable of adjusting a ratio of internal diameter to external diameter continuously in a wide range. <P>SOLUTION: The illumination optical device for applying luminous flux from a light source to a surface to be irradiated with light has a first prism group having a plurality of prisms, a second prism group having a plurality of prisms, and a prism group selection means for selecting the first prism group or the second one for introducing into an optical path. By moving at least one of the plurality of prisms in the first or second prism group introduced into the optical path in the direction of a light axis, the a ratio of internal diameter to external diameter of luminous flux emitted from the first or second prism group is changed. The upper-limit value of the ratio of internal diameter to external diameter of luminous flux emitted from the first prism group is equal to or more than the lower-limit value of luminous flux emitted from the second prism group and is smaller than the upper-limit value of luminous flux emitted from the second prism group. <P>COPYRIGHT: (C)2009,JPO&INPIT |
