METHOD AND DEVICE FOR DETECTING FOCUSING POSITION

摘要

PURPOSE:To automatically make focusing at high accuracy without dispersion by providing a photoelectric sensor made up of an aggregate of minute sensors smaller than the particle image of an original picture at the image forming position of a pickup lens. CONSTITUTION:A photoelectric sensor (CCD) 34 such as CCD etc. is placed at a position where a diaphragm 4 and optical distance become equal. Light from an original picture 2 is reflected by a movable mirror 33 and the real image of the original picture 2 is formed on the CCD 34. The CCD is the aggregate to many cells, i.e. minute sensors, and the output can be led out from each micro sensor. When a color particle or a silver particle forms an image on the CCD 34, the size of th one minute is set to become smaller than the size of one particle image. The steepness of density distribution near the border line of the particle image is calculated and evaluated according to an evaluation function prepared beforehand based on output from the micro sensors. A moving mechanism 40 is driven to make the result of calculation indicate maximum evaluation, and a pickup lens 3 is moved to focus position for the original picture 2.