Distance and focal length combined are magnification.
Originally Posted by 2F/2F
The most important thing about DOF, by far, is that it is a perceptual thing. Not an 'autonomous' entity with an absolute dimension. (Despite all the formulae and calculators people like to let loose on it).
The best definition is that as "acceptable unsharpness".
Very clear about that it is a judgement, a perception, and not a measurement or dimension.
Still pretty vague, since it provides no clue about what sharpness is.
You can increase DOF dramatically, not by changing magnification or f-stop, but by changing how 'sharp' the sharp bit is. A good film and good lens produce shallower DOF than a bad lens on bad film. And vice versa. Simply by changing the difference, the visual contrast between realy sharp and not so sharp.
Another undefined thing is viewing distance.
The final magnification counts, so DOF gets less if you blow a negative up more.
But only if you do not increase viewing distance accordingly.
So a giant print can appear to have greater DOF than a small print of the same negative, if only you view the giant print from relatively further away than the small print.
Last edited by Q.G.; 07-08-2009 at 02:36 PM. Click to view previous post history.