As many of you know, I have recently built a 6x12 format camera with a 65mm SA lens. I originally intended to fit the lens to be focused at the hyperfocal distance for f16 but in the end, I fitted it with a helical focus mechanism. I want to know if there is a formula for determining the amount of forward movement (or bellows extension if on a view camera) for the lens position to focus at a given distance. The things I know already are: Lens focal length: 65mm Lens flange distance: 70.5mm Suggested focus point for hyperfocal: 8.8 feet (5x4 film distance from dofmaster website). So with these figures, is it possible to calculate how much further forward the lens needs to be from its 70.5mm flange distance in order to be focused at 8.8 feet or is it easier to put it on a view camera, focus and measure the distance? Steve.