40D + 100-400 + 1.5x TC problems

Last weekend I decided to use my 100-400 and 1.5x TC since the wind was blowing so hard there wasn't going to be any possible way to hold the 500. Anyways, back to the problem.

I couldn't get it to autofocus on anything. I was using AI Servo. At first I thought it was a lens problem, but I put it on the XT and it focused fine. Later when I got home, I put the 100-400 on the 40D (no TC) and it worked fine too.

So does the 40D not like the TC (non-reporting) when the 100-400 is attached? I used this combo all the time on the XT without a problem.

40d shouldn't autofocus with the tc and 1-4 on there. it's not supposed to work with autofocus on lenses with a max aperture of 5.6. I've heard about taping the pins, but i think that's the 30d and older models.

I shouldn't need to tape pins since this TC doesn't report.

Only 1D bodies can auto-focus at f/8... not much about reporting, but rather, the actual amount of light reaching the AF sensor.

badams,

I've read conflicting posts about whether different models do or don't work with converters. Some users insist that on certain models it's impossible while others claim thats nonsense.

All I know is that with my 30D, using a Kenko C-AF 1.4x PRO 300 DG I needed to tape three of the eleven pins for the 100-400 to AF. With the pins taped it AF's perfectly. Before I bought the PRO 300 I tried a cheaper Kenko 1.4x and did not need to tape any pins.

Maybe the difference between your 1.5x and my 1.4x makes a difference, I just don't know.

I have a 30D and I know that my Tamron-F 1.4x C AF1 MC4 will autofocus on my Canon 500mm f4.5 L. I just attached it to my Canon 100-400 L and it autofocused just fine.

I think that the more expensive teleconverters ( Pro ) models are the ones that fail to autofocus past f5.6.

I bough my Tamron 1.4x a long time ago, used, and I did not use it because I thought it would degrade the image too much. About a year ago I tried it on the 500 and was amazed how well it did. It has bailed me out several times since.