| 摘要 |
In an apparatus, a collimated-beam irradiating unit irradiates on the target a substantially collimated beam with a size thereon. A first pickup unit causes the photodetector to pick up through the imaging optics a first image of the target while the substantially collimated beam is being irradiated on the target by the collimated-beam irradiating unit. A measuring unit measures size information indicative of the size of the collimated beam being irradiated on the target based on the picked-up second image. A distance determining unit determines a distance between the apparatus and the target based on the measured size information of the collimated beam.
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