AF teleconvertor question

[Wrench]

Had a quick Q about a 2x converter for my 10D. I was at Ritz tonight and mounted a quantaray 2x on my 10D that said it was for AF Eos mount.....it worked, except the auto focus. Manual worked though. What's different? Do they make one specifically for the digital line? Thx.

[wolf]

You lose 2 f stops with a 2x teleconverter so you need a fast lens or you will lose AF when using a 2X teleconverter.

[defordphoto]

For more information on lenses and much more, try this VERY informative thread: http://photography-on-the.net/forum/showthread.php?t=22081

A 2x TC is usually used as a last resort. On some lenses you will lose AF. The prosumer cameras (10D Drebel, 20D) are programmed to not auto-focus at f8 or smaller. As an aside Quantaray lenses are about at the bottom of the barrel when it comes to anything close to quality.

Buyer beware. Read the thread above. There's a wealth of information there that may save you from making a bad decsision.

[robertwgross]

There was an older Canon lens mount that did not do autofocus.

This teleconverter causes a loss of two stops. If you started with a very fast lens and then lost two stops, your lens and camera body might be able to still autofocus. The body's limit might be f/5.6 or f/8 or something. However, if you started with a slower lens and then lost two stops, your autofocus will be lost beyond the limit. That's pretty normal.

It helps you reacquainted with your lens's manual focus ring.

---Bob Gross---

[DaveG]

Had a quick Q about a 2x converter for my 10D. I was at Ritz tonight and mounted a quantaray 2x on my 10D that said it was for AF Eos mount.....it worked, except the auto focus. Manual worked though. What's different? Do they make one specifically for the digital line? Thx.

Lenses on a 10D have to be quicker than 5.6 to work with the AF. If you put the 2X on a lens slower than 2.8, then that's probably why it won't autofocus.

But along with cheap the quality you get from a TC of this level is terrible. A lot of users even dismiss the Canon extenders, although I'm not one of them. You've got a good camera and I presume good lenses and Quantaray is low end garbage. Keep walking.

[robertwgross]

This is kind of an unwritten thing, but there is a difference in performance between teleconverters. I can't quantify this, but I can see something when I place two teleconverters side-by-side on the table. Look at the Canon unit, and then look at the lower grade unit. Look at the physical diameter of the lens element in there.

I just have to believe that one is letting more light through, or at least with less optical distorsion.

---Bob Gross---

[Wrench]

Thanks for all of your help. I'll stay away from the TC then and just get another lense. I know quantaray isn't the best but I have one of their lenses and it works OK. I don't like it as much as my Tamron. I just don't have the money for Canon, I know others on here are in the same boat. What is a good brand for glass that wont break the bank? thx.

[defordphoto]

As an FYI I have both the Canon 1.4 and 2.0 TCs. :) Several members here do.