| 摘要 |
PURPOSE:To always fix a focus detecting point in a photographing screen by providing asymmetrically a pupil for projection and a pupil for photodetecting on one of planes containing the surface of an object and an optical axis of a photographic lens, and the opposite side, respectively, and bringing a reflected light from the object to light-guiding to a photodetector through a reflecting mirror which has been brought to reflection arrangement vertically to said plane. CONSTITUTION:At the photodetecting side, a reflected light from an object being in a position corresponding to points P1, P2 and a reflected light from an object being in a position corresponding to a point P3 are condensed by a pupil 5a for photodetecting and a pupil 5b for photodetecting, respectively, and the reflected light corresponding to the point P2, and the reflected light corresponding to the points P1, P3 are brought to light-guiding to a sensor 9 directly, and after having been reflected by a mirror 10b, respectively. In such a way, the optical path length through which the reflected light corresponding to the points P1, P3 reaches a focal plane directly is made the same as the optical path length through which said light is made incident on the sensor 9 on the focal plane through the mirror. In such a way, one of projection elements is selected and lighted, one arbitrary point among three points on the screen is selected, and a focus in its position is detected, therefore, however varied a focal distance of a photographic lens may be, a focus detecting point can always be fixed in a photographing screen. |
