You can get a sense of how DOF varies in different situations but
plugging representative numbers into a calculator program such as
this one online:
http://www.dofmaster.com/dofjs.html
Various rules of thumb get bandied about, but they are no substitute
for really checking the math in the specific situation that you're
concerned with (35mm vs. 4/3 etc.)
The question of how depth of field is different with digital cameras
has confused more than a few people. I lay the blame squarely on the
industry's use of "equivalent 35mm focal lengths," a convenient
fiction but which often leads to incorrect assumptions. Quoting
angles of view would be something new to most people, but much less
confusing.
I think this is all clearer for people who have some history of using
medium format cameras--where, for example, a 105mm lens might give a
"normal lens" angle of view.
Hold all the following constant:
Lens angle of view
f/stop
final image size and viewing distance
acceptable circle of confusion for that image size
...and the smaller the format, the deeper the depth of field.
cheers,
--Ross
~~~~~~~~~~~~~~~
Ross's photo gallery:
http://flickr.com/photos/vox
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