Which teleconverter will autofocus with the Canon 100-400mm?

I know that this has been discussed before but -

 

I'd like to add a 1.4X teleconverter to my Canon 100-400mm lens and I

understand that with the Canon it won't autofoucus. So, what is the best

alternative in order maintain the autofocus function?

Use a third party teleconverter. However, they will only TRY to get autofocus. There is no guarantee that it will be either fast or accurate. Either way, you'll have to manual focus most of the time.

Any time the efective aperture is smaller than 5.6 the autofocus won't work. (I read this in the Canon literature.) The lens is at 5.6 once you zoom out to 250mm. I'm not sure of the math, but I'm guessing that since the largest aperture is 4.5 a 1.4 teleconverter would equate to a 6.3 lens at best.

I use a Kenko Pro 300 DG 1.4x and tape the 3 pins on the left (looking at it from the lens side). My 100-400 retains AF when using the TC with the pins taped.

<I>Any time the efective aperture is smaller than 5.6 the autofocus won't work.</i><P>

 

I believe that depends on the body and lens(es) used. A 1-series camera (1D, 1Ds, etc) can still use the center AF point with some lenses and the 1.4x TC up to f/8.

Forgot to mention that the 100-400 retains AF on my 5D and 20D.

Any body with 45-point AF (1D's, 1Ds's, 1v and 3) can AF to f8 with the centre point and will therefore work with the that lens and the 1.4x TC.

 

Kenko and Tamron TC's don't communicate effective aperture so may work unreliably on bodies with lesser AF units. Sigma TC's won't AF if the lens+TC combo gives less than f5.6.

Marvin,

 

before I switched to digital a few years ago, I got a 1.4 teleconverter to use with my 100-400mm lens to use with my Rebel film camera (rebel 2000 at the time). As a rugby photographer, I found that autofocusing was slow, if not difficult, plus since the sport I shoot is fast paced, a good action shot is missed as the focusing was too slow for my liking to catch the moment.

 

that said, I stopped using it, as I found this process frustrating, and returned to my normal shooting ame plan, and got the results I wanted in the end, shot-wise. I still ahve the teleconverter, but haven't used it since I switched to digital.

 

sheryl

Marvin, you don't mention what camera body you will using this for. As has been mentioned some Canon bodies have no problem focusing with f/8 (effective), although there are some restrictions about which AF sensors can be used this way.

 

I found that f/8 (f/5.6 lens with Kenko 1.5x TC) worked pretty well with a Canon 300D/D-Rebel, barely ok with a Elan II, and not so good with a 20D. Of course different lenses and TC combinations might work differently with this. Above, Don W. says that the 100-400 works with Kenko Pro 1.4x on a 20D, so it can work.

 

Don's Kenko Pro TC's must be the type that reports the effective aperture loss. That's why he has to tape the contact pins. You can do the same with Canon TC's. The cheap third party versions work without the tape, but you get what you pay for too.

I have been using the Kenko 1.4x teleconverter with the Canon 70-300mm 4-5.6 on my Digital Rebel with reasonable success. As has been written here, you need light to do AF. I can shoot at f8 and that means 5.6 with the TC on. Even then, it is not a quick focus and frequently there is a good degree of seaching. When that happens, I switch to MF. Roger