TC autofocus - 100-300 f5.6L

[Mircula]

Hello,

does anybody know if any 1.4 teleconverter is compatible with my old Canon 100/300 f5.6L?

I would like to still have autofocus as the manual focus on this lens is just awful to use.

I read that the canon 1.4 will not do that as it only autofocuses with zoom lenses aperture f4 and larger. Is that correct.


Somewhere else i read that some cheaper kenko converters sometimes work even with zooms of 5.6 aperture.

Is there a list or some table in the internet to look this kind of stuff up?



Cheers.


Mirc

[Wobbles]

Mirc,
1. The Canon TC's physically won't fit on your lens.

2. Yes, the Kenko Pro TC's will fit, however you need to tape over (i.e. small piece of electrical tape) the first three pins to "hide" the TC from the camera. AF will work but you will need a lot of light and/or contrast for it to work reliably. Optically they are the best quality after the genuine Canon TC's

3. There are also the Tamron SP TC's, not as good optically, but will work without taping the pins.

Cheers
John

[Riverlander]

[QUOTE]I read that the canon 1.4 will not do that as it only autofocuses with zoom lenses aperture f4 and larger. Is that correct.[/QUOTE
Yes - with qualifications,,,,, :D

Canon, in their wisdom, have a feature in their cameras that disallows auto-focus unless the maximum aperture of the attached lens is greater than a set figure. For your 40D that figure is f/5.6.
Thus the attached lens MUST be f/5.6, or faster, for the camera to TRY to auto-focus.

If you attach a 1.4x TC you lose one stop of light, so your 100-300 f/5.6L effectively becomes an f/8 lens, and the camera will not even try to auto-focus. The camera gets this information via the 3 pins mentioned above (Google it - there are plenty of references) and if those pins are taped over the camera will not get the information and thus it will TRY to auto-focus.

The camera may/will have trouble getting the auto-focus to lock onto the subject and you may get serious "hunting" which could be detrimental to the lens motors. "Tape at your own risk."

Sometimes -- seems to happen more with Sigma stuff than Canon - if you attach the TC to the camera, and then attach the lens to the TC, you will find that the camera is not aware of the TC being there at all!!!! Your camera will report that an f/5.6 lens is attached (instead of f/8) and will auto-focus (sometimes with difficulty).
If you get this situation you will find that the auto-exposure is also wrong and your images will bw over-exposed by 1 stop unless you make in-camera adjustments.

[Mircula]

Hello,

Thank you very much for that info.

I also called canon and they said this lens is not at all compatible with any of their teleconverters....

i guess a f8 lens is not really useful to me....

Ahhh well....No longer focal lenght for me i guess :(