Thanks Chuck,
Interesting indeed.
Been away at mother's place, just catching up a bit. -finished
edging/weeding all beds, mulch applied, condensate central A/C hose
replaced--asked Home Depot plumber for the "Really Right Stuff-"--vinyl
tubing that would not kink, silicone tape on the one junction--repair
son is 500mi away so no failures permitted.
On surface seems to directly contradict Cambridgeincolour post.
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm
But not really on closer inspection. FL is indeed a minor factor until
approach hyperfocal distance or high magnification. Articles
discussing flip side of the same coin. Quote of footnote in the
Camincol article "
"*Note: We describe depth of field as being virtually constant because
there are limiting cases where this does not hold true. For focal
distances resulting in high magnification, or very near the hyperfocal
distance, wide angle lenses may provide a greater DoF than telephoto
lenses. On the other hand, for situations of high magnification the
traditional DoF calculation becomes inaccurate due to another factor:
pupil magnification. This actually acts to offset the DoF advantage
for most wide angle lenses, and increase it for telephoto and macro
lenses. At the other limiting case, near the hyperfocal distance, the
increase in DoF arises because the wide angle lens has a greater rear
DoF, and can thus more easily attain critical sharpness at infinity for
any given focal distance."
I am not sure about the pupil magnification issue for macro--I've
always ignored it. Though it may foul up any dof calculations, I think
it really only affects the "effective aperture" so the DOF at the same
true exposure is not really changed--anything else would violate the
sacrosanct "no free lunch" principle of optics.
Mike
Very timely. Jan and Mike should find this interesting. Here's more
on
DOF and focal length (by Ctein) from The Online Photographer:
<http://theonlinephotographer.typepad.com/the_online_photographer/2009/06
/depth-of-field-hellthe-sequel.html>
Chuck Norcutt
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