100-400L IS with 2x converter

[sweepiedog]

If I use my 100-400L IS with a canon 2x converter will I lose my autofocus ????

[chris maddock]

The short answer is yes, it won't even try to AF. Third-party TCs often don't tell the camera what combination is fitted, so it will try but may only be less than 50% successful

There is a trick on Fred Miranda's website, where you apply tape to the last three contacts on the TC and it stops the camera from knowing what lens combination is fitted so it does at least try.
This is reasonably successful with the 1.4x TC, but only may work with the 2x and very good light and a very contrasty subject.

The above is for use with the D30/D60 which have a spec of f5.6 for reliable AF. I believe the 1D can go to f8, which means that the 1.4x should be no problem without the tape trick and the 2x may work with it.

HTH
Chris

[adamsmith]

http://www.usa.canon.com/eflenses/lenses/ef_2x/ef_2xsample2.html

According to this Canon chart, the 100-400 + 2x converter makes AF "impossible".

-Adam

[Andy Somnifac]

As adam pointed out, no, it won't work. When combined with the 2x TC, the lens would have a maximum working aperture of f/9.5 which puts is it beyond the AF capabilities of even the 1D. You can try the tape trick, but there are reasons that those pins are there I would imagine. If the camera would AF properly (given a reasonable success rate) at that aperture there would be no need for them, would there?

Andy