| 摘要 |
An optical system having a light source portion, a light receiving medium receiving the light beam from the light source portion, and a light condensing optical system for condensing the light beam from the light source portion as a beam spot on the light receiving medium, the light condensing optical system having provided therein an area in which the light beam becomes a parallel beam, said area having disposed therein an afocal zoom lens, whereby the diameter of the beam spot can be continuously varied.
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