d300, sigma 50-500 and teleconverters

[Isurus]

Hi everyone
I have the first two of the 3 items above and am looking for a teleconverter to go between them; do any allow AF?

Thanks

[Telecorder]

The Bigma will mount both the Sigma EX 1.4X TC and the Kenko Pro 300 DG 1.4X TC (I have all three - wanna trade my D50 for your body?)

One must rack out the zoom and lock to teleconverter to move the rear elements out of the way to mount the TCs -- critical for the Sigma EX TC.

Both will AF but the Sigma will need the first lens' side contact tape to disable the communications...
http://forums.dpreview.com/forums/read.asp?forum=1021&message=23560898&q=sigma+50+500+tc&qf=m

I'm yet to do any extensive IQ comparison testing on my Bigma + TCs to determine which offers the better IQ but its on my agenda... Image below is a monopod mounted D50 + Bigma + Kenko at 500-mm...

Unless in good light, fast shutter and using good support techniques, a monopod or stable tripod is almost mandatory for long end imaging with a TC.

Both AF if subject has a good contrast for sensor to pick up on. Low light + low subject contrast will probably result in some AF hunting at times...