On Wed, 26 Feb 2003, Butch Black wrote: > I agree that the same focal length lens will produce aprox. the same > DOF regardless of format. In the above example if you cropped a 35mm > neg to APS size, aprox = to a 75mm lens and you shot the same image at > the same spot with a 75mm lens (not cropped) and blew both up to the > same size, they would have the same DOF. My question, maybe best > answered by D100, D30, D60 owners, is with the APS sized sensor is the > DOF the same or greater then shooting with the equivalent 35mm lens?
If you're comparing focal lengths directly, DOF is the same. If you're comparing field of view, it's different. To explain... If I use a lens with a focal length of 50mm on a 35mm camera, I will get the same DOF that I'd get if I put a 50mm lens on a DSLR, or on a 645, or on a 6x7 camera. If I take a picture with a 50mm 6x7 lens on my Pentax 6x7 camera, and then take a shot at the same aperture with a 50mm lens on this new Pentax DSLR, the DOF will be the same. If I crop the 6x7 photo so that it has the same field of view as the DSLR shot, the DOF and perspective will in theory be identical... the two shots will look the same if you ignore grain, tonality, etc. Now, if you compare field of view, DOF will appear to be greater on the DSLR than it will on a 35mm shot or a 6x7 shot. The reason for that is the wider the lens, the more DOF you get. If I need a 50mm lens for my 35mm film camera to cover a certain field of view (say, a head and shoulders shot), then I'm only going to need a 33mm lens to cover the same field of view with a DSLR that has a 1.5x magnification factor. Because I'm using a wider angle lens (33mm instead of 50mm), I'm getting more DOF in the DSLR shot. OTOH, if I kept the focal lengths the same by using a 50mm lens on each, then my DOF would be the same but my DSLR shot would look like it was shot with a 75mm lens. The quick guide to comparing a 35mm film camera and a DSLR with a 1.5x factor: (a) 50mm lens on DSLR, 50mm lens on film SLR --same DOF --same perspective --DSLR has less field of view and greater apparent magnification (smaller sensor on DSLR, so only center of image is recorded) (b) 33mm lens on DSLR, 50mm lens on film SLR --DSLR has more DOF --perspective is different --field of view and apparent magification are the same chris
