| 摘要 |
PURPOSE:To make it possible to accurately detect the focal point of an object of any size by using a detecting element of large area having a small detecting cell. CONSTITUTION:The image signals having passed through an objective lens 21 are reflected by a half-mirror to reach an image detecting element 23. A monolithic photodiode, MOS photoelectric element or CCD photoelectric detecting element is used as the image detecting element 23. When the real image of the object is to be focused by the objective lens 21 upon the image detecting element 23, it is possible to generate the signals which have their optical contrast highly varied. If the respective cells of the detecting element 23 are made sufficiently small and if the output signals of the adjacent detecting cells are compared, there is a case, in which a remarkably difference resides in the output signal intensities of the two adjacent detecting cells. The output signals of the detecting cells 31 to 33 are compared so that the correct focal point is formed on the object at any distnace. |
