Originally posted by devorama Does anyone know if the DoF scales on the DA lenses are based on the 1.5x crop sensor? I just recently learned that the DoF scale on the old full frame lenses assumes a full frame sensor, and should be decreased by a factor equal to the crop factor of the sensor. This is due to different sizes of the Circle of Confusion.
Crop factor is irrelevant. Crop factor refers to the FOV, the Field of View -- that is, the angle that the lens sees. DOF is determined ONLY by the aperture and focal length of the lens, and the distance to the subject. A smaller sensor or frame just means that you (and the camera) see a narrower slice of what's out there -- it doesn't change the depth relationships.
Say you have a 100mm lens, aperture is f/11, subject is 12 meters (40 feet) away. You use the same setup on 8x10 and 4x5 view cameras (wide), 645 and 6x9 MF cameras (nearly normal), 35mm FF and HF (same as APS-C) cameras (tele), and a 110 SLR (long tele). Because of the different frame sizes, the FOV angle changes greatly -- but the DOF remains exactly the same, from 7m (23 ft) to 30m (100 ft). All that changes is the width of what's captured.
EDIT: Darn, JeffJS, ya beat me to it! I shouldn't have stopped to look at a lens. ;(