Just to chime in a bit here ... a few things haven't been said clearly.
Many camera auto-focus systems refuse to work when presented with a lens of less than f/5.6. The top-of-the-line Canon "1" series cameras will happily auto-focus down to f/8. Canon 300D, 350D, 10D and 20D all want f/5.6 or better.
I shoot with Canon, I don't know what happens with Nikon (or other) equipment.
With the Canons there is a way to 'trick' the camera regarding the maximum aperture of the lens. A bit of tape over 3 of the electrical contacts between the lens and the converter will prevent the converter from being reported. This leaves the camera believing that it is using the straight lens and it will at least try to auto-focus. I say try because, due to the dimmer light with the teleconverter, it may not be successful.
A second thing that kills auto-focus (regardless of teleconverter use) is the lack of light or low contrast targets. Of course some cameras handle this situation better than others.
|