Image sharpness detecting system and apparatus utilizing the same

Claim 1

An image sharpness detecting system cooperating with an image-forming optical system to detect an optimum degree of sharpness of an image projected thereby from an object comprising: light-to-electrical signal converting means positioned at a point of substantial focus of said optical system; detecting means connected to the output of said light-to-electrical signal converting means upon variation of the electrical output signal for detecting an optimum degree of sharpness of an image of the object; said light-to-electrical signal converting means including: first photoconductive means having an electrical characteristic associated therewith, said means having at least a pair of electrodes and a photoconductive element of such a geometry as to establish a current path of wide width and short length with the photoconductive material sandwiched in between said electrodes along the respective entire wide widths of said element, second conductive means having an electrical characteristic associated therewith, said means having at least a pair of electrodes and a photoconductive element of such a geometry as to establish a current path of narrow width and long length with the photoconductive material sandwiched in between said electrodes along the respective entire narrow widths of said element; said electrical characteristic of both first and second photoconductive means having a peak value when the sharpness of the image to be formed thereon becomes maximum; and optical means arranged between said first and second photoconductive means for adjusting the ratio of total incident light intensities on the surface of said two means so as to compensate for differences between the resulting lightresponsive characteristics of said first and second photoconductive means, whereby the optimum degree of sharpness of the image of the object which may be encountered can be detected with high accuracy even at low light levels.