Auto focus with teleconverter.

I'm about to pick up a 100-400 and would like to get a 2x teleconverter to use for longer shots. Do teleconverters support autofocus and IS? If so, which brands do? I have a 7D if that makes any difference.
Thanks in advance!

IS, yes; you'll lose AF with a 2x on the 100-400, as that will drop your max aperture to f/11.

I had ok results with the 2x MkIII TC + 100-400, when I was testing out the 2x with my 70-200; but the 'Pump' was manual focus only with it. So I couldn't justify keeping it when it didn't work for anything on the 70-200.

blakeG! wrote in post #13960399
I'm about to pick up a 100-400 and would like to get a 2x teleconverter to use for longer shots. Do teleconverters support autofocus and IS? If so, which brands do? I have a 7D if that makes any difference.
Thanks in advance!

Do a search, the Kenko Pro 300 DGX 1.4x teleconverter works on the 100-400 with autofocus and IS

You will lose autofocus on this lens with any Canon extender, on anything but a 1D camera. A 1.4 will make the f5.6 into f8 and a 2X will be f11. You lose one and two f-stops respectively with the TC's. There is a way to fool the camera and make it try to autofocus by putting scotch tape over certain electrical contacts (I tried it) but it's unreliable and still realllllly slllooowww to focus except in real bright sunlight. Not worth it.

So you lose autofocus with the 2x. if I were to get a 1.4 tele, I would keep autofocus and IS?

on a 7d yes

blakeG! wrote in post #13960574
So you lose autofocus with the 2x. if I were to get a 1.4 tele, I would keep autofocus and IS?

Maybe. Some of the 1.4s won't report the focal length change to the camera and AF will remain on; however, it still may slow down and/or be inaccurate enough to not be worth it.

All you can do is try and see how you like the results.

[EDIT: PS; don't get the Canon 1.4. The Kenkos tend to give better results in that range of TC]

Snydremark wrote in post #13960598
Maybe. Some of the 1.4s won't report the focal length change to the camera and AF will remain on; however, it still may slow down and/or be inaccurate enough to not be worth it.

All you can do is try and see how you like the results.

[EDIT: PS; don't get the Canon 1.4. The Kenkos tend to give better results in that range of TC]

I plan on getting a kenko. Along with kenko extension tubes for my macro work

Don't bother with the extender on a 100-400 lens unless you plan on using it with manual focus. You will only be disappointed if you expect ANY AF capabilities.

fredrikb81 wrote in post #13961333
Don't bother with the extender on a 100-400 lens unless you plan on using it with manual focus. You will only be disappointed if you expect ANY AF capabilities.

I will mostly be using it for moon and bird shots. With birds that far away, I should be able to use live view to focus pretty spot on.

When I used a 1.4x TC with the 400 f/5.6 when I had it (taped pins) AF was terrible. But it still was nice to have the reach, and just pre-set the focus via live-view... For birding and such.

Don't expect great image quality with a teleconverter on a zoom. With a few exceptions (such as the Canon 70-200/2.8 IS Mark II with the Canon 2X Mark III), teleconverters work best with prime lenses.

A 1.4X "costs" one stop of light and a 2X "costs" two stops. So an f5.6 lens with a 1.4X added "becomes" an f8 lens. And a 2X on the same lens makes it an f11 lens. Technically, Canon cameras other than the 1D series are not supposed to be able to auto focus with less than f5.6 lens. You might still be able to manually focus, but your viewfinder will be dimmer too.

There are some tricks to try to get the lens to try to auto focus with a teleconverter. Use a third party TC that doesn't "report" to the camera. With TCs that report, you can tape up a couple of the electronic contacts so the camera doesn't know it's there. There are illustrations how to do this here on POTN and elsewhere on the Internet. Do a search if interested. Either way, the EXIF will only show the lens, not the lens + TC focal length.

However, "tricking" the camera will give reduced AF performance. It will be slower and it will hunt more... might fail more in lower light or lower contrast situations.

And adding the optics of a TC always costs some image quality. Less with a weaker TC (1.4X) than with stronger ones (2X). It can be very little loss with more ideal lens/TC combos... or a lot with less ideal combinations. In general, the 100-400 is not a very good zoom to use with teleconverters. But some people make it work adequately for their purposes.

Have you considered simply getting a longer lens, instead? For example, the Sigma 150-500mm lens alone might serve better than a 100-400 with a 1.4X. The Sigma also costs about $500 less.

Personally having tried the combination of a 7D+100/400+Kenko 1.4TC (with the pins taped ) in good light I would not bother just stick to the lens +camera.
The 7D +100/400 is quite croppable, one of the benefits of 18MP.
This is about 70 yards away from my house and while there is not much feather detail I would not expect it at that distance.

AF will work in LiveView with any combination of lens + extender e.g. 400mm f5.6 plus 2x extender. It's very slow, but useable for stationary or slow moving objects. Best to focus just past the subject as the af always seems to go from far focus to close and back again until it finds focus. Therefore, it takes much less time to lock on if you firstly focus just past the subject.

Thank you for all the input everyone. Greatly appreciated. I'm guessing a tele would have a lot better IQ with a prime. Such as the 400 5.6. Decisions decisions...