| 摘要 |
PURPOSE:To save electric power and to increase a detection speed by deciding on focusing speedily when the integral value of the output of a photodetecting element attains to a focus detectable level. CONSTITUTION:Light emitted from a projected element 3 passes through b1 to strike an object, and is reflected irregularly to pass through an optical path b2, forming an image on a photodetecting element 6. When the image is in focus, the reflected light of the projection spot image P is photodetected in two areas 6A and 6B on the sensor with the same quantity of light, and the integral values VA and VB of their outputs have no difference. When the image is not in focus, the integral values have difference, so the photodetecting element 6 is moved until the difference is eliminated to move a lens 1 associatively. For the purpose, a means which detects the integral values attaining to a specific level and a means which detect the large/small relation between both integral values VA and VB exceeds the specific level are provided, and a focusing decision is made immediately when one of the detecting means operates. |
