At 12:32 PM -0700 7/5/05, Jim Brick wrote:
At 08:21 AM 7/5/2005, David Young wrote:
Yet the DOF is so small at such focal lengths, that the nose and teeth are fuzzy, to the point where the entire photo looks unsharp. And closing down does not seem to make any appreciable difference, at least until you get to the point where you can't use the view finder, and it all becomes pointless.
David,
Depth Of Field is a function of f/stop and image size. An 80mm lens on a 4X5 has precisely the same DOF as an 80mm lens on a Hasselblad, which has exactly the same DOF as an 80mm lens on a Leica, or a 1.6x digital sensor, in every situation. One does not give less or more DOF than the other.
Image size is a direct function of the focal length, nothing else. Your DOF is based entirely on the 800mm optic (400x2,) not the 1280mm equivalent optic. If you stuck a piece of Minox film over the sensor, you might get a 2000mm equivalent optic, but the actual optic is still 800mm. So everything is based on 800mm, regardless of the film/sensor size.
Here is a DOF calculator:
http://www.outsight.com/hyperfocal.html#dof
Which explains the digital LMF (Lens Multiplier Factor) which you are then told to use the lens actual focal length in the calculations, not the equivalent focal length.
Jim
Hi Jim,
http://www.photo.net/learn/optics/dofdigital/
-- * Henning J. Wulff /|\ Wulff Photography & Design /###\ mailto:henningw@xxxxxxxxxxxxxx |[ ]| http://www.archiphoto.com
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