AUTOMATIC FOCUSING DEVICE

摘要

PURPOSE:To perform accurate automatic focusing even when an image is low in contrast by detecting the variable density level of an interference fringe and regarding the position of a variable density level larger than a specific value as a focusing position. CONSTITUTION:A sample 20 is moved as shown by an arrow A to form the interference fringe. Variation in the variable density level of this interference fringe is detected through a slit 27. A reference light mirror 24 is so positioned previously that the variable density level output value of the interference fringe is maximum when the sample is in focus; and the value of the detection signal of the interference fringe when the sample is within the depth-of-focus range of an objective 23 is predetermined and the sample 20 is set where the variable density level of the interference fringe is larger than the value, attaining automatic focusing. Consequently, the precision of the focusing is irrelevant to the contrast of a real image of the sample, so the automatic focusing is accurate even when the image has low contrast.