| 摘要 |
PURPOSE:To decrease transmission systems in number and to simplify constitution, by using either one of two distance information on focal length and subject distance and the movement extent of an image plane, and then finding the other piece of distance information. CONSTITUTION:The extent DELTAX of displacement of the image plane from the image formation plane of an actual object image is detected by a focus detector 14 and a reversible motor 19 is driven forward or backward by the outpt of a control circuit 18 to perform focusing. As the motor 19 rotates, a signal for the movement extent of the image plane is obtained from a comparator 25 in the control circuit 18 through the pattern 23 of generating device 22 and 23 for the signal for the movement extent of the image plane. In infinite-distance focusing, when the extent of displacement is DELTAX, focal length is (f), and subject distance is R, R=f<2>/DELTAX+2f. For this purpose, only the (f) is transmitted from an interchangeable lens and the output of said comparator 25 is used as the DELTAX. Consequently, the R is calculated on a camera side, it is not necessary to obtain the R from the interchangeable lens side, and transmission systems are decreased in number to simplify the constitution. |
