MECHANISM AND METHOD FOR DETECTING FOCUS

PROBLEM TO BE SOLVED: To provide a focus detecting mechanism which detects a focus using image signals for which a sample image is captured and further detects highly accurate focus position. SOLUTION: The focus detecting mechanism includes: an illumination light source 1 for performing emission to a sample; an imaging optical system including a first photodetection means 23 for outputting the image signal of the sample; a relative distance change means 9 for changing a distance between the sample and the focus of an objective lens; a control means 32 for driving the illumination light source; a position detection means 11 for detecting the position in the optical axis direction of the objective lens or a sample stage; a second photodetection means 4 for monitoring the light quantity of illumination light; and a signal processing apparatus 40 for outputting focusing position information. The signal processing apparatus 40 includes: a means 44 for calculating the contrast of the sample image; a means 45 for normalizing the calculated contrast using monitor signals; and a means 46 for detecting the position of the objective lens or the sample stage for maximizing the contrast on the basis of a series of relations between the normalized contrast and the position signal. COPYRIGHT: (C)2011,JPO&INPIT