1. A method of determining focus for an image capture system using scene content within an image, comprising the steps of: a) acquiring, from the image, image data having different focus positions; b) dividing the image data into sub-images; c) calculating a sharpness value for each sub-image; d) calculating an image sharpness value for each focus position using the sub-image sharpness values; e) plotting the image sharpness value versus the focus position; f) fitting a curve to the plot of the image sharpness values versus the focus position, wherein the curve has a peak sharpness value; and g) determining the focus of the image capture system from a point on the curve.