| 摘要 |
PURPOSE:To prevent erroneous detection in the case where a face to be detected is approximated to a condenser lens, by arranging an aperture in the optical path of a reflected wave from the face to be detected. CONSTITUTION:In the in-focus state shown in a figure (a), outputs Va and Vb of two light receiving faces 19a and 19b of a photodetector 19 are equal to each other, and an error detection signal Ve is zero. If a face 15 to be detected is deflected to a position more distant than the focus position, the signal Ve is positive. If the face 15 to be detected is deflected to a position nearer than the focus position, the signal Ve is negative. If the face 15 to be detected approaches a condenser lens 14 furthermore, the beam diameter of reflected light 16 should be larger but is controlled by an aperture 18. In this case, the signal Ve has not the polarity inverted if the size of the aperture 18 is so determined that this beam diameter does not exceed the beam diameter for the in-focus state. Consequently, the state where the face 15 to be detected is approximated to the condenser lens is not detected erroneously as the state where the face to be detected is more distant from the condenser lens. |
