> Has anyone on the list had experience using
> a TC-14a or TC-16a with the AF 180 ED 2.8
>(non-D if it matters)?
I've used them together a bit -- but just playing around.
I haven't printed anything larger than a 4x5.
> I have tried a few shots w/ the TC-16a and
> some show vignetting, some don't - I suspect
> it has to do with shutter speed, though I
> can't see how.
I don't know how shutter speed could affect vignetting either.
The only exposure warning I've heard of regarding fast lenses
on teleconverters is that the aperture doesn't stop down as
fast with the TC in the middle, so if you're going from f2.8 to f22
the aperture will still be closing during the first part of the
exposure. At fast shutter speeds, the change in aperture can
be large enough to cause uneven exposure.
You might want to test to see if it has something to do with
how far the TC's elements have to be shifted to bring the lens
into focus. As you probably noticed, the TC-16a has to shift
it's elements quite a bit to shift the focus on the 180. It's
possible that the TC is shifting its elements far enough that
they're not fully covered by the 180's image. See if manually
focusing the lens to the general vicinity of the subject
before starting the AF affects vignetting.
-Don
