Archived posting to the Leica Users Group, 2003/04/24
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]On Fri, 25 Apr 2003 10:10:43 +0800, Red Dawn <reddawn@singnet.com.sg> wrote: ... > > u got me wrong. Wat i was comparing was using a Canon 50mm f1.4 lens on a > digital SLR like the EOS 10D, where the effective focal length would be > 50 x > 1.6 = 80mm, versus usng a true 80mm lens like the Summilux R 80 f1.4 on a > Canon EOS 1v film body, or a R8 for that matter. > > BOTH configurations will have the same angle of view, and will be able to > frame the same subject with the same composition and magnification, and > produce pictures with the same DOF. > > Hence this thing about digital not being able to get enough shallow DOF > is > simply a fallacy. With digital SLRs that are not full frame, you got to > change your mindset - a 50mm lens is NO LONGER a 50mm lens and does not > give > a field of view of a normal 50mm lens anymore!!!!!!... Forget about digital, for a moment. The concept of "effective focal length" is kinda bogus. The focal length of a 50mm lens is 50mm. Period (to be repetitive). Take a picture with a 50mm lens on a regular 35mm camera with a 24x36 image frame, and crop it down to the field of a digital sensor, what you have is a cropped image from a 50mm lens. Cropping does not change the focal length, effective or otherwise. Now, do not move the camera (assume it is on a tripod). Remove the 50mm lens and put on the 80mm lens (or use a zoom lens :-)). You get an image with the same composition, 1.6x (or so) larger -- but with reduced depth of field, based on my memory and experience. I have in the last few minutes tried an approximation to this experiment using a Canon G3, and zooming instead of changing lenses. Guess what -- the results validate the theory. Without moving the camera, the depth of field at the longer focal length was dramatically less then that at the shorter length, after adjusting the images to the same apparent size. Gee -- why am I surprised? I was a mathematician! Try it yourself using your own camera and lenses. You will be convinced. - -- Clive http://clive.moss.net - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html