In a method of determining focus in an image capture system of the type having an image sensor, optics for forming an image of a scene on the image sensor, and an image processor for determining the best focus, an image is acquired such that the focus of the image changes continuously, line by line, across the image. A plurality of edges above a predetermined magnitude are detected in the image and the sharpness of the detected edge is measured. The sharpest edge in each line of the image is determined and plotted versus the location of the line in the image. A curve is fit to the plot of sharpness versus location and the best focus of the imaging system is determined from the peak of the curve fit.