JPS6478205A - Detecting method for defocusing quantity - Google Patents

Abstract

PURPOSE:To detect the defocusing quantity of a photographic lens with high accuracy by correcting the defocusing quantity with a correcting value for the image formation position of the photographic lens corresponding to a ratio calculated from a predicted information quantity and the quantities of object information obtained with circumferential light and auxiliary light according to a previously found relation. CONSTITUTION:An image of an object is formed by a focus lens group 20A, varied to proper magnification by lens groups 20B and 20C, and formed on an image pickup surface through a master lens group 20D. Then when the photoelectric output waveform of a CCD line sensor 32 to the object image is deviates, the defocusing is detected from the quantity and direction of the deviation. For a correcting means, the ratio of the information quantity by the auxiliary light and the information quantity by the circumferential light, etc., are in the constant relation with the movement quantity of the image formation position of the photographic lens, so this relation is found in advance. Then the defocusing quantity is calculated from object information detected when the auxiliary light is used and the current correcting value is found to correct the defocusing quantity. Consequently, the defocusing quantity of the photographic lens is detected with high accuracy regardless of the quantity of the auxiliary light and the quantity of circumferential light.