David,
See between your lines:
----- Original Message ----- From: "David Zaninovic" <[EMAIL PROTECTED]>
To: <[email protected]>
How much extension did you had to add to that macro lens ?
About 100mm. Note that I used it with the *istD, which needs less extension to avoid vignetting than a full-framed film camera.
You also focused the macro as close as possible, right ?
Yes.
Were you able to shoot at f11-f22 without vignetting ?
Had to. DOF is miniscule at >4x. (shooting snow crystals)
Does the extension that you add have more effect than the built-in extension or it is the same thing ?
Doesn't matter, you'll need both with the 28mm.
Is the rear element on the FA 100/2.8 fixed or it moves depending on the focus ?
Fixed. It has nothing to say with re. vignetting, afaik.
I see that the built-in extension on my lens has very little difference in regard to vignetting so I am afraid that I would have to add to much extension tubes which would be unmanageable.
There's no free lunch. :-)
If you plan to work from the top of a tripod, you should consider other options than stacked lenses. A reverse adapter and a 28mm will give you 2x right out of the box and a much less fiddly combo to work with. If you can live with stopping down your lens manually. Mark Cassino has done some wonderful macro stuff with a reversed 50mm. Check out http://www.markcassino.com.
Is there any automatic extension tubes that would pass the electrical contacts as well as aperture control so I can keep P-TTL.
Pentax flashes can deliver TTL even with screw-mount lenses, but don't have any hopes for P-TTL.
hth,
Jostein
