| 摘要 |
PURPOSE:To attain the detection of a focus by providing a means converging at least a part of a reflected light or a transmitted light by an object to be irradiated, and a photodetector detecting the change in the luminous amount distribution at a face not perpendicular to an optical axis near the converging point. CONSTITUTION:In the figure, 9 is a condenser lens and 10-12 are luminou flux from the body to be irradiated. For example, in the device the luminous flux is 10 when the objective is focused to a disc face, and when the objective is parted from the disc face or approaches the disc face, the luminous flux is respectively 11 and 12. In observing the luminou amounts distribution at a face 13 not perpendicular to the optical axis near the converging point, the luminous flux is concentrated nearly on the center at focusing but when the disc face approaches or is parted, the distribution is biased respectively in B and C directions. The focus is detected by detecting the change in the luminous amount distribution. |
