100-400 AF Problem?

[Theo]

Have the DRebel w\ the 100-400L + the 1.4TCII. Auto Focus worked fine the 1st 2 months through the whole focal range with the TC added, but now it won't even attempt to auto focus with the TC! 100-400 AF works Fine Straight on the DRebel and my 70-200 f4.0 Auto Focuses Fine with the TC! Cleaned the Camera-TC-Lens Contacts, but the 100-400 + TC AF is Still Dead!

Canon wants All 3 (Camera-TC-Lens) Back for Testing and Adjustment, but thought I'd ask Here for any Suggestions Before going that route!!

Thanks,
Ted
http://img.dpreview.com/images/one.gif
http://img.dpreview.com/images/one.gif

[PacAce]

Have the DRebel w\ the 100-400L + the 1.4TCII. Auto Focus worked fine the 1st 2 months through the whole focal range with the TC added, but now it won't even attempt to auto focus with the TC! 100-400 AF works Fine Straight on the DRebel and my 70-200 f4.0 Auto Focuses Fine with the TC! Cleaned the Camera-TC-Lens Contacts, but the 100-400 + TC AF is Still Dead!

Canon wants All 3 (Camera-TC-Lens) Back for Testing and Adjustment, but thought I'd ask Here for any Suggestions Before going that route!!

Thanks,
Ted
http://img.dpreview.com/images/one.gif
http://img.dpreview.com/images/one.gif

The 100-400 isn't supposed to AF with the 1.4x TC on the DRebel. It won't even AF with the 10D nor the 20D. AF with that combo will only work with the 1D series cameras. There's nothing wrong with your 100-400, 1.4x or the camera.

[RichardtheSane]

I'm suprised Canon did not pick up on this.

Although by trying to autofocus in the first place that could indicate a fault - maybe that is why Canon want it back?

[phili1]

The highest F stop the 20D will focus with is F6.3 I beleive the 300D it's F5.6 and when you put the extender on you might get it at 100 & 200 but loose on the 20D but you lost it at 100 with the 300D because you are at F 6.3 and it can only focus at F5.6.