On 8/30/2011 8:10 PM, C.H.Ling wrote:
> I understand the DOF/image size issue but long lens has shallow "appearance
> DOF", even the calculated DOF are the same the longer lens give softer
> background. So I have mentioned you need to stop down for the DOF. Stopping
> down the short lens will give harsh background while the long lens still
> maintain a soft one.
>
> With the test I just made, I found a strange thing, looking at the edge of
> the can the 300mm give sharper image with similar magnification and same
> aperture. I have double checked the aperture and focus point and focus was
> done by liveview very carefully. It seems that DOF cannot be governed by a
> simple formula.
Give that man a (choice of edible or smokeable prizes)!
All the DOF formulae that we grew up with use the thin lens assumption and were
based on observation of human viewings
of B&W prints taken with film.
It seems clear to me that they are no more than general guidelines with very
complex lenses, digital sensors and digital
viewing.
There's a related discussion on TOP today on Ctein's topic, "Will the Sony
NEX-7 Suffer Diffraction Effects?", with at
least a couple of quite interesting responses.
<http://theonlinephotographer.typepad.com/the_online_photographer/2011/08/nex-7-diffraction-effects.html>
Mine, which may or may not be interesting, suggests that Ctein might revise his
article to say "Always look at actual
pictures and let your eyes be your guide."
I conclude "The map is NEVER the territory."
I have simply seen too much stuff that doesn't agree with theory to take
theory's word for the actual territory. BTW,
with 20/10 vision, my DOF tables would be different anyway. :-)
Moose
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