| 摘要 |
PURPOSE: To restrain the low-contrast scanning to the minimum and to realize a high-speed AF. CONSTITUTION: The device detecting the focusing state of an imageformation optical system by obtaining a focusing degree evaluation value based on an output signal from a photodetector 13 which picks up the image of a subject being an observed object is equipped with a field diaphragm 11 arranged at a conjugate position to a subject image, a field diaphragm driving means 22 changing the diameter of the field diaphragm, a low contrast decision means judging whether or not the contrast value of the subject image is insufficient to detect focusing, a diaphragm diameter control means stopping the diaphragm diameter until the field diaphragm image is projected on the photodetector train 13 in the case where the contrast is insufficient, and a focusing direction detecting means detecting the focusing direction by comparing a 1st contrast value obtained in a state where the field diaphragm image is projected on the photodetector train 13 with a 2nd contarst value obtained after changing a relative distance between the subject and an objective lens 5. |
