Focus condition detecting device

Claim 1

An automatic focus detecting device, comprising: an objective lens for forming displaced first and second images; first and second image signal generating means, having first and second sensors positioned to receive the first and second images and adapted to generate first and second image signals corresponding to the light intensity distributions of the images on the first and second sensors, respectively; correlation calculating means for calculating correlation between the first and second image signals while repeatedly shifting the second image signal relative to the first image signal by a given pitch to provide a correlation value of each shift with the corresponding amount of each shift; best correlation finding means for finding a best correlation among the plurality of calculated correlations to produce a best correlation value; contrast detecting means for detecting the contrast of one of the images on the first and second sensors; interpolation calculating means for carrying out an interpolation calculation to find a true best correlation in accordance with the best correlation value, the detected contrast, and a smaller correlation between a correlation in front of and another correlation behind the best correlation along the shifting direction, and focusing condition detecting means for detecting focusing conditon of the objective lens with respect to the object in accordance with the true best correlation.