| 摘要 |
A so-called active-type focus detection device applicable to optical instruments such as camera is provided with light emitting means and photoelectric detector means disposed at two positions conjugate with the pre-arranged focal plane of an image-forming optical system whose focus adjusted condition is to be detected or two positions optically equivalent to the two conjugate positions, and the light emitted from the light emitting means is projected toward an object to which the camera is to be focused, through the image-forming optical system. The light then reflected by the object is received by the photoelectric detector means through the image-forming optical system and the focused condition of the image-forming optical system with respect to the object is detected in accordance with the electrical output of the photoelectric detector means. According to a preferred embodiment of the present invention, the light emitted from the light-emitting means is projected upon the object by utilization of the maximum half area of the effective aperture of the image-forming optical system while, of the light that is reflected into the image-forming optical system by the object, the light passing through the maximum other half area of the effective aperture of the image-forming optical system is directed to the photoelectric detector means, whereby the position of incidence of the light flux on the light-receiving surface of the photoelectric detector means is varied correspondingly to the focus adjusted condition of the image-forming optical system with respect to the object and the variation in position of incidence of the light flux on the light-receiving surface of the photoelectric detector means is detected in accordance with the electrical output of the photoelectric detector means, thereby detecting the focus adjusted condition of the image-forming optical system with respect to the object.
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