Canon supertelephoto autofocus above f5.6

FourRingCircus

FourRingCircus

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Anybody out there with a 500mm F4L (or 600mm) may know this already, but I recently discovered it and it's not something I've heard about so I thought I'd share.

Normally, if you stick a 2xTC on a native F4 lens, (or a 1.4x on an f5.6) you will loose autofocus. This may not be the case on 1D bodies but it's certainly the case on 5D/7D.

I was messing about with live view last week and had the 2xTCIII on my 500(ISII). To my shock (and quite by accident), I noticed the focus was working and I got a green rectangle confirmation of focus. I pressed to zoom the live view to 5x and 10x and I (eventually) got a spot-on focus again!

It's not quick - in fact, it's horribly slow, but it works very well. Spot-on focus at 1000mm was quite a revelation.

Can't say if this will work for a version one IS lens or an earlier 2x but it would be interesting to try if, like me, you can never get close enough.:bonk:
 
Live view AF should work with pretty much any lens at any aperture, given decent light. It uses contrast-detect AF, working off the actual sensor image, and is quite independent of the normal phase-detect AF system that needs a certain minimum aperture to function.

There are reports emerging that in fact the 1DX will AF normally at f/8, eg 800L f/5.6 with 1.4x extender. Maybe a quirk of that particular combo. 5D3 has the same AF system so that might work too. Or not. These things tend to be unpredictable.
 
I thought all the 1 series could AF at f/8 anyway? Im sure my Mk3 used to. :thinking:
 
Aah right, didnt know that, any idea why Canon have changed it?
 
Thanks Bob :thumbs:, now if only i could afford one!
 
...as usual, Bob beat me to it.....go off on hols again, Bob, give the rest of us a chance!!
:bonk:
 
When you actually check about it is one of these things that, it works for some people and not others. Some are using reporting TCs some aren't. Some are using Canon TC some are using Kenko. Some say Canon MKII TCs are better for it than the MKIII. Some people using the same camera, lens, TC combo can get it to work whilst others can't.

This is the first thing I saw about it recently and dug about from there. http://www.birdsasart-blog.com/2012/08/30/mega-amazing-discovery-800-f5-6-1-4x-tc-canon-eos-1dx/

WEX photographic have a Canon teleconverter compatibility chart on their site but it doesn't take into account the limitations of the 1DX, beware.
 
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