Anthony wrote:
(snip) > > DOF has to do with the focal length and the f-stop. Print > magnification has nothing whatsoever to do with it. > - But print magnification has EVERYTHING to do with it. Until now I have kept my silence WRT this subject but no more. Too frequently anecdote and intuition have been been offered as informed knowledge. The facts follow. The DOF concept is based on the circles of confusion (COC) of the out of focus part of a photograph being either smaller than the unaided eye can appreciate, in which case the subject matter will seem acceptably focussed, or large enough for the same unaided eye to see the unsharpness of it. Quite simply, when the enlargement factor of a print is increased then the COC of nearly focussed areas will become larger and will cross the threshold between small enough to pass as sharp and large enough to be deemed unsharp. REPLY: This is a mix-up of terms. The original poster is right; DOF has nothing whatsoever to do with enlargement factor in the finished print. Sharpness, not DOF depends of magnification when the area is constant. Otherwise, both DOF and sharpness are constant the moment you press the shutter. The scale on the lens says what sharpness is adequate (which is a highly subjective matter - DOF is not). If you increase reproduction ratio everything will experience reduced sharpness at a certain area equally but DOF is constant. DOF depends of four factors only: 1) F- stop. 2) Focal lenght. 3) size of the subject. 4) camera- subject distance. The reason why medium format display less DOF than 35mm is that for a certain F:stop, certain size of the subject and certain camera to subject distance focal length will be longer on MF hence displaying less DOF. P�l - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
