| 摘要 |
An illumination system which ensures a numerical aperture larger than the orientation characteristics of a light sources and achieves uniform yet bright illumination is provided. The illumination system includes a light source, a collector lens constructed and arranged to converge light emitted from the light source to substantially parallel light beams and a relay lens constructed and arranged to transmit the substantially parallel light beams to an objective. The collector lens includes a first positive lens group, a second negative lens group, and at least one aspheric optical element. The working distance WD of the collector lens satisfies 0.5<WD/f<1.5 . . . (1) where WD is the distance from the center of the light source to the apex of a surface in the collector lens, the surface is located nearest to the light source side, and f is the focal length of the collector lens.
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