What extender is best for me?

This will be on my 5DmkII & my 100-400 f/4.5L IS USM.

Thanks for your suggestions!

Canon 1.4x

The 100-400 is not fully compatible with either extender, unfortunately. You might get it to work, but you'll lose autofocus, except with the 1.4 on 1-Series bodies.

1.4X is ALWAYS better than 2X. With 2X, too much IQ is lost.

what are you photographing?

You can retain AF on a 550D, 7D and a 5D2 with the 100-400 usinf a Kenko Pro300 DGX 1.4x converter. I know this because I've done it, although the AF starts to hunt a bit in poor light. In good light the AF is fairly rapid and accurate, though maybe not fast enough for "action" shots it's certainly fast enough for most every day shooting.

rick_reno wrote in post #14190348
what are you photographing?

Mostly wildlife & landscape.

modchild wrote in post #14190449
You can retain AF on a 550D, 7D and a 5D2 with the 100-400 usinf a Kenko Pro300 DGX 1.4x converter. I know this because I've done it, although the AF starts to hunt a bit in poor light. In good light the AF is fairly rapid and accurate, though maybe not fast enough for "action" shots it's certainly fast enough for most every day shooting.

Thanks, I'll look into one of these!

jeff

modchild wrote in post #14190449
You can retain AF on a 550D, 7D and a 5D2 with the 100-400 usinf a Kenko Pro300 DGX 1.4x converter. I know this because I've done it, although the AF starts to hunt a bit in poor light. In good light the AF is fairly rapid and accurate, though maybe not fast enough for "action" shots it's certainly fast enough for most every day shooting.

I don't have the 100-400 and use the Canon Mark II teleconverters on other lenses... But I've often heard and seen the Kenko recommended, so that would be my suggestion, too. Supposedly it's at least as good in terms of image quality (or minimizing loss of the lens' image quality) as the Canon 1.4X. But, just as importantly, because it doesn't "report" on the camera, the camera doesn't know it's there and it should continue to try to focus in reasonably good conditions. You'll likely need to restrict the AF to the center point only.

Any teleconverter "costs light" reaching the sensor and AF array. A 1.4X costs one stop of light. A 2X costs two stops. So an f5.6 lens such as the 100-400 becomes an effective f8 when a 1.4X is installed and an effective f11 when a 2X is installed.

Technically, only the Canon 1D series cameras can still focus with f8 or slower lenses (well, the old 1V and EOS-3 film cameras could too). The other cameras are limited to f5.6. In each case, only the center AF point continues to work at the smallest aperture.

Canon cameras and teleconverters are designed to recognize what's being used... and to turn off AF when the camera's limit is reached. If you see the teleconverter in the EXIF (i.e. a 500mm lens shows as a 700mm focal length when a 1.4X is installed)... then the camera is recognizing it... and will turn off AF when the camera's limitation is exceeded.

Some third party teleconverters are not recognized by the camera and the Kenko Pro 300 DG/DGX appears to be one of those. So your EXIF will show an incorrect focal length (that 500mm lens example would still show as 500mm even after the TC is installed). But, the camera will still try to focus... In good light it might be fine a stop or even two lower than it's limit, though it's likely to be slower and more inclined to hunt. Poorer light and/or subjects with little contrast and detail will be more difficult.

There's a trick with the Canon or any of the teleconverters that "report" to tape up two of the electronic contacts on the rear of the TC so the camera doesn't know it's there. That will allow the AF system to try to focus, same as a TC that isn't recognized at all. If interested in trying this, search here on POTN for more info about what pins to tape over. It's a temporary modification.

In general, the stronger a TC, the more image quality it will cost, too. And, in general, zooms don't work as well with TCs as prime lenses do. However, specific combinations can be exceptions and work fairly well.

Note, too, that there are two Kenko 1.4X models... an "MC-4" and a "Pro 300 DGX". The latter is their better quality and more expensive model. In general I wouldn't expect the same level of performance out of the less expensive 1.4X "MC-4" model, though it might work fine with some lenses.

The current Canon 1.4X Mark III is considerably more expensive than the 1.4X Mark II model it's replacing. I'm not sure that the new model will outperform the earlier model in any very significant way, except possibly on some of the newest lenses. The 2X Mark III appears to be a more dramatic upgrade, seems especially well matched with the 70-200/2.8 IS Mark II that was introduced about the same time. (I was never very impressed with the 2XII combined with the first version of that lens. I have occasionally used the lens with the 1.4XII and it's okay.)

amfoto1 wrote in post #14190665
I don't have the 100-400 and use the Canon Mark II teleconverters on other lenses... But I've often heard and seen the Kenko recommended, so that would be my suggestion, too. Supposedly it's at least as good in terms of image quality (or minimizing loss of the lens' image quality) as the Canon 1.4X. But, just as importantly, because it doesn't "report" on the camera, the camera doesn't know it's there and it should continue to try to focus in reasonably good conditions. You'll likely need to restrict the AF to the center point only.

Any teleconverter "costs light" reaching the sensor and AF array. A 1.4X costs one stop of light. A 2X costs two stops. So an f5.6 lens such as the 100-400 becomes an effective f8 when a 1.4X is installed and an effective f11 when a 2X is installed.

Technically, only the Canon 1D series cameras can still focus with f8 or slower lenses (well, the old 1V and EOS-3 film cameras could too). The other cameras are limited to f5.6. In each case, only the center AF point continues to work at the smallest aperture.

Canon cameras and teleconverters are designed to recognize what's being used... and to turn off AF when the camera's limit is reached. If you see the teleconverter in the EXIF (i.e. a 500mm lens shows as a 700mm focal length when a 1.4X is installed)... then the camera is recognizing it... and will turn off AF when the camera's limitation is exceeded.

Some third party teleconverters are not recognized by the camera and the Kenko Pro 300 DG/DGX appears to be one of those. So your EXIF will show an incorrect focal length (that 500mm lens example would still show as 500mm even after the TC is installed). But, the camera will still try to focus... In good light it might be fine a stop or even two lower than it's limit, though it's likely to be slower and more inclined to hunt. Poorer light and/or subjects with little contrast and detail will be more difficult.

There's a trick with the Canon or any of the teleconverters that "report" to tape up two of the electronic contacts on the rear of the TC so the camera doesn't know it's there. That will allow the AF system to try to focus, same as a TC that isn't recognized at all. If interested in trying this, search here on POTN for more info about what pins to tape over. It's a temporary modification.

In general, the stronger a TC, the more image quality it will cost, too. And, in general, zooms don't work as well with TCs as prime lenses do. However, specific combinations can be exceptions and work fairly well.

Note, too, that there are two Kenko 1.4X models... an "MC-4" and a "Pro 300 DGX". The latter is their better quality and more expensive model. In general I wouldn't expect the same level of performance out of the less expensive 1.4X "MC-4" model, though it might work fine with some lenses.

The current Canon 1.4X Mark III is considerably more expensive than the 1.4X Mark II model it's replacing. I'm not sure that the new model will outperform the earlier model in any very significant way, except possibly on some of the newest lenses. The 2X Mark III appears to be a more dramatic upgrade, seems especially well matched with the 70-200/2.8 IS Mark II that was introduced about the same time. (I was never very impressed with the 2XII combined with the first version of that lens. I have occasionally used the lens with the 1.4XII and it's okay.)

Tanks for your great info!
Jeff