Canon Teleconverters (extenders)

[Vectisbirder]

I have a Canon L-series 400mm f5.6 lens and would like to get a teleconverter for it, most likely one of the Canon ones.
Obviously I would like as much reach as humanly possible, but keeping as much image quality as I can, hence going for a Canon one, rather than a cheaper alternative. As I use a 40D I know that I will lose AF, unless I tape the pins, but that's not a problem.

My questions are these, would I be better going for the 1.4x or the 2x extender? What are the pros and cons of each? Would I be best off going for the 1.4x and relying on a bit of judicious cropping, or the 2x, bearing in mind I'll lose 2 stops of light rather than one?

I also have a question about pin-taping - it makes the AF work but, as this is slow and presumably a bit of a struggle for it, could this eventually cause the AF to fail and need repairs?

Thanks

[Ollie]

Don't know about Canon converters but I occasionally use A Kenko pro 300 1.4x with my Canon 400mm f5.6L lens and it works reasonably well with the pins taped. Auto focus is a bit erratic though and tends to hunt a bit so I usually use manual focus with the converter on.

Only my personal opinion but I wouldn't use a 2x with mine as you would need extremely good light because as you say you lose a couple of stops with the 2x.

Would think you would have to use it for a pretty lengthy period for the AF to fail although I suppose it's a possibility

Roger

[BillyPilgrim]

Better to go for the 1.4x as the drop in image quality will hardly be noticeable, if at all.

You don't need to go for the Canon as Sigma and Kenko are just as good. And a second-hand Sigma or Kenko will probably be less than half the price of a Canon so there's no contest.

[Vectisbirder]

Thanks folks.

[Hobjob]

1.4 for me too.

I get a drop in sharpness with that and my 100-400 though
(and I have tried another 1.4 and it was the same).