No option for AF w/400 5.6 and tele?

[brett_cole]

Is there no teleconverter that when used on a 20D/400 5.6 combo will retain AF?

Doesn't seem like it.

[JosvanEekelen]

Most third-party converters will retain autofocus but it will probably hunt. You can also tape some of the contacts on the converter.

[geoffs1]

I'll be the Kenko TCs like the <a href="http://www.adorama.com/Refby.tpl?refby=rflAID062012&sku=KN2XPDEOS">PRO 300 "DG" AF 2x</a> and <a href="http://www.adorama.com/Refby.tpl?refby=rflAID062012&sku=KN14XPDEOS">PRO 300 DG AF 1.4x</a> would work. I've not tried them on a Canon (I own the Nikon version), but they generally don't inform the camera body of their presence, so the aperture and focal-length don't appear to change. AF does get a bit slow in low light. - GSS

[rainer_t]

This thread ...

 

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00KQGG

 

... might be interesting to read.

[brett_cole]

Again you've found the appropriate thread when I was unable to. Thanks again.

[brett_cole]

Again you've found the appropriate thread when I was unable to. Thanks again.

[DickArnold]

I just posted this on another very recent thread in response to the same question about the use of a Tamron or Kenko extender.

 

I took a few pictures on a new Manfotto tripod and trigger type ball head this afternoon with the Tamron F 1.4 and my 100-400 4.5-5.6 IS. I was shooting outdoors and it was a little windy so I shot a thousandth with apertures varying by a stop. I am not a lens tester and did not control my variables that well. I did use mirror lock up and no IS. My conclusion is that I will put the Tamron 1.4 in my bag. If I need 890 mm focal length I will use it. The AF is slower but not by much in bright light. I took some highly saturated flowers and by gosh the color did not differ hardly at all IMO. I would post them but nothing is very conclusive at low resolution and I don't think you would see very much difference. As for sharpness I think there was difference of course but the extender pictures looked usable on my computer. If I were still doing sports I certainly would try it there. The way my old newspaper printed pictures you certainly could not judge sharpness. I am not a lens tester to repeat myself so I will now pass to Bob Atkins to say something more credible than I am capable of. Anyway we'll see how it works out. It is better in IQ than my Canon 2X that doesn't AF on this lens. I made a couple of 5x7 prints and you could frame them and no one would know the difference. Dnd of post.

 

This extender was stowed away in a drawer. I was surprised at how well my lens focused. Here is another post I made in that forum.

 

Alistair. I have a 100-400 4.5-5.6L. I have had a Tamron F 1.4 extender sitting in a drawer for several years. I just pulled it out and put it on an XTi and the above lens. The damn thing auto focuses like a champ. The aperture does not read right in the XTi but it actually reads the light correctly because I just made a bunch of photographs with and without and they are identical with the shutter speed reducing by a stop when the 1.4x is installed. It just thinks the lens is at 5.6 instead in the indicator instead of F8. I am kind of dumbfounded by the fact it works so well. I did not tape the left three contacts looking into the back of the extender as recommended in the Fred Miranda D30/10D hints. This gives an equivilent of a little over 900mm. I always assumed the 1.4 would not fit on the lens. I have a 2X. I am not sure yet about the IQ 1.4 but the Canon 2X has always been somewhat marginal on my 70-200 2.8L. The 2X will not focus on the 100-400 at all and I would not use it for serious pictures on that lens. I will take a few comparison pictures tomorrow to determine if I would use the 1.4 for anything serious. Anyway thanks for raising the subject

[DickArnold]

I took some low light pictures also and AF still worked effectively with the Extender.