>From Bob Atkins article on Pnet:
http://photo.net/learn/optics/dofdigital/
"Here are the answers:
For an equivalent field of view, the small-sensor camera has at least
1.6x MORE depth of field than a full-frame camera would have - when the
focus distance is significantly less then the hyperfocal distance (but
the full-frame format need a lens with 1.6x the focal length to give
the same view).
Using the same lens on a small-sensor camera and a full-frame camera,
the small-sensor image has 1.6x LESS depth of field than the full-frame
image would have (but they would be different images since the field of
view would be different)
If you use the same lens on a small-sensor camera and a full-frame
camera and crop the full-frame image to give the same view as the
digital image, the depth of field is IDENTICAL.
If you use the same lens on a small-sensor camera and a full-frame
camera, then shoot from different distances so that the view is the
same, the small-sensor image will have 1.6x MORE DOF then the film
image.
Close to the hyperfocal distance, the small-sensor camera has a much
more than 1.6x the DOF of a full-frame camera. The hyperfocal distance
of the small-sensor camera is 1.6x less than that of a full-frame
camera. "
This is mostly old hat and Chuck is certainly correct in his
statements--(not suprising given the stable of in-house consultants he
has.)
I trust CH kept the autotube or bellows in the same position as the
effective aperture would indeed change
as the DOF is governed bythe effective aperture not the lens setting.
No need to worry about PMF as the lens is symmetric.
Couple of things I see: Have read in an assignement at Focus School
that oversampling with a greater number of
diffraction limited pixels still renders more detail than a fewer
number of larger pixels. This really should not alter DOF per se but
how that translates visually I don't know. May expalin in part what is
apparent to the eyes. The other wild card is keeping the
postprocessing equivalent.
The "apparent dof" increase using shorter FL lens at an equivalent
subject size by moving closer is easier to explain in many situations.
The distribution of the dof changes with a shorter FL and a larger % is
behind the plane of focus. Seems the DOF is often judged more by the
background than foreground.
Assistant to Dr. Focus, Mike
--
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