Abstract: In a focus detection system for detecting focus condition of an objective lens, there is disposed a pair of photosensor arrays each having a plurality of photocells lined up in one direction to receive a first image and second image passed through respectively a lens system and the photosensor arrays produce first original signal groups and second original signal groups each signal groups corresponding to light intensity of the images projected thereto. A processing device processes the original signal groups in such a manner that the first original signal groups are respectively divided into a plurality of blocks, and one of the blocks of the first original signal groups is selected and it is detected that in what group in the selected block best coincidence occurs.

Abstract: A device for measuring convergence of a color CRT periodically generating a test pattern in a predetermined portion of a screen of the color CRT including signal output means for outputting a signal corresponding to glow timing of the test pattern generated on the screen, image pickup means for picking up the test pattern on the screen to output an image signal, control means responsive to output of the signal output means for controlling the image pickup means so as to output the image signal during the time that the test pattern is not generated in the predetermined portion of the screen, and calculation means for calculating a convergence assessment value of the color CRT based on the image signal.