| 摘要 |
PURPOSE:To execute a correct focusing detection by detecting a ratio of one out-of-focus function for evaluating a distinction of an image and other out-of-focus function, comparing this value with a constant, and executing a focusing decision by selecting an evaluation of an out-of-focus image or a horizontally shifted image. CONSTITUTION:An intensity of an image photodetected by each photodetector train 10, 11 and 12 becomes the largest when an image forming position exists on a photodetecting surface, and becomes small when it is shifted from the photodetecting surface. In this case, when the photodetecting surfaces of the photodetector trains 11, 12 are positioned on surfaces 13A, 13B before and behind an expected focal plane 9, and the image forming position is in a focusing state, the distinction becomes the highest on the photodetecting surface of the photodetector 10, and its output becomes like a step. In this case, on the photodetecting surface of the photodetector trains 11, 12, it takes an optical path difference of a prescribed distance DELTA, and as for a shift quantity delta of an output curve of an A group and a B group of the photodetector trains 11, 12, its absolute value is equal and its value is also small, but as said position becomes a non-focusing state, the absolute value becomes equal and the value also becomes large. Accordingly, by both the outputs of the photodetector trains 11, 12, the focusing detection is executed by detecting a horizontally shifted image in an area where an out-of-focus is large, and detecting an out-of-focus image in an area where it is in focus to some extent. |
