| 摘要 |
An optical focus detecting apparatus for an optical system includes a focus scanning and spatial frequency filter comprising a rotating chopper disc. The disc is arranged at an angle with respect to the axis thereof whereby the disc focus position is oscillated back and forth through a predetermined plane, which plane may comprise the film plane of a camera. The disc includes a plurality of transparent and opaque radial sector pairs, the widths of the sectors of any pair being the same and randomly different from the widths of the sectors of adjacent pairs. The sector pairs are so relatively arranged that sector pairs of substantially identical widths are repeated at positions displaced 180 DEG on the disc whereby the modulation of the image optical spectrum is random in nature. The distribution of transparent and opaque sectors is such that the average transmission of light by the disc is 50 percent of the incident light.
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