> > 2. Wide aperture on ANY lens reduces DOField but decreases
DOFocus.
TYPO WARNING: That should have been " ... increases DOFocus."
> You're probably right here. My point was that a 12mm extension tube
on a
> 20mm lens will probably leave you with no usable focusing range.
True: I tried the 12mm tube on a 20 ... and it is unusable.
> I don't have a 12mm tube, but I do have a "mini optical bench"
(actually an
> odd bracket thing I picked up at a camera show years ago). I mounted
my EOS
> 1N and placed my 21-35 in front of it with the lens flange 12mm from
the
> camera flange. At 21mm, focusing range was from 1/2 inch (at
infinity) to
> 1/4 inch (at .5 meters) from the front front lens element.
Interesting, but
> not very practical.
A true 20mm lense should work fine on bellows; that is a nice lens
designed for high magnification macro work. They tend to be fairly
symmetrical though.
Bob
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