500 f4L IS and 2x Teleconverters

I already own the 1.4 extender, which is almost permanently attached to my 500

f4 lens, but sometimes I need the additional reach of a 1000mm lens for static

objects (hawks perched for example). I would like to maintain autofocus if at

all possible - so here's the question.

Can I trick the Canon 2x extender to autofocus by taping some of the pins, or

should I get the Kenko Pro 2x - I know the Kenko will autofocus when taped.

I understand the limitations of the 2x extenders and the slow autofocus with

the resulting f8 aperture, but sometimes a less than optimal shot is better

than no one at all:-)

Thanks for any help.

Juergen

I assume you don't have a 1-series camera (these work fine at f8, albeit with just the center

AF point). I tried the 'tape trick' with my 500/4 + Canon 2X on a 30d, and results were not

good: it would attempt to AF but there was a lot of jerky 'hunting' for correct focus, and

often it never did lock onto the subject. I suspect that it could work in bright light with a

contrasty target, but wouldn't place any bets.