| 摘要 |
PURPOSE:To prevent the occurrence of an erroneous focusing operation due to the unevenness of the distribtion of the quantity of light on the sensor surface, by dividing one of two image- forming luminous fluxes, to which a luminous flux is divided, into three approximately equally in respect to the quantity of light and forming random mirror patterns on the surface of a variable area beam splitter. CONSTITUTION:One image-forming luminous flux 14 of two luminous fluxes to which a luminous flux is divided by a mirror 12 is divided and reflected by variable area beam splitters 91, and 92 and a mirror 93, and image-forming luminous fluxes 101, 102, and 103 are divided so as to have an approximately equal quantity of light and are led to CCD sensors 111, 112, and 113. The quantity of light and are led to CCD sensors 111, 112, and 113. The quantity of blur of the formed-image which is generated by the difference of length of optical length among three luminous fluxes is detected by sensors to detect the focusing state. Many small holes whose area corresponds to the third of the overall area of the surface of the splitter 91 are provided at random on the surface of the splitter 91 crossing the luminous flux 14 to form mirror patterns. The distribution of the quantity of light obtained by scanning the formed-image, which is generated through small holes, on the sensor 111 has a certain periodicity, and the variance of the quantity of light is restrained in accordance with calculation, and the erroneous focusing operation is prevented. |
