A method for optimizing focus of an optical system passively includes the following steps: discretizing optical positions with respect to precision requirements; initializing an idle counter to zero, going to the initial optical position, initializing a best position to current position, clearing a sharpness array; calculating correspondence; adding a sharpness value to a sharpness array; calculating a longest increasing subsequence on the sharpness array; checking if the longest increasing subsequence length increases; clearing the idle counter; setting the best position to the current position; incrementing the idle counter; checking if the termination threshold is reached; checking if the current position corresponds to the end of discrete optical positions if the termination threshold is not reached; driving motors to the next position; optionally improving the best position; going to the best position and terminating the method.