Using a 2xTc

Richard Rickard · #1 September 18th, 2008, 02:40 PM

I have a 20D and I purchased a Mark II to use My 2x Tc on a trip I took. Sold the Mark II because of the weight.
Only using the Mark series can you AUTO focus a lens using a 2 X TC.
My question is, will we be able to use a 2X Tc and auto a lens using the new 5d Mark II.
It is a bad thing and I do not like the way Canon has it that we can not use a 2 X TC with a 20D , 30D, 40D, 50D or a rebel, we can ONLY us our 2 XTC on a MARK SERIES.
I have a 2 X TC sitting in my bag and can not us it( BAD Canon)

Richard Rickard

Doug Kerr · #2 September 18th, 2008, 03:07 PM

Hi, Richard,

Quote:

Originally Posted by Richard Rickard

I have a 20D and I purchased a Mark II to use My 2x Tc on a trip I took. Sold the Mark II because of the weight.
Only using the Mark series can you AUTO focus a lens using a 2 X TC.

Well, I wouldn't say that. It depends on the maximum aperture of the composite lens (basic lens plus the focal length converter) and the minimum aperture that is workable for the various type of AF point detectors in the body.

Many EOS bodies (not just the 1 series) offer AF detectors that will work at apertures of f/5.6, and so long as the basic lens has an aperture of at least f/2.8, then operation with a 2x focal length converter should be practical.

Nill Toulme · #3 September 18th, 2008, 06:33 PM

You can also use it even with lenses slower than f/2.8 by taping over certain contacts on the lens mount, but the AF performance tends to be shaky when used that way (i.e., Canon disables it for a reason).

Nill

Richard Rickard · #4 September 19th, 2008, 04:28 AM

Canon does not make 2.8 in a 500 or 600. And how would you handle a truck like that.
Using a 2 Xtc to get extra length with a 300mm 4/0 can not be done. Only short lens like a 70-200 2.8
makes sense or a 300 2.8, but then you have to spend a lot of money to do this.

Don Cohen · #5 September 19th, 2008, 04:34 AM

I feel your pain, Richard, but I don't think it's fair to blame Canon. It doesn't hide the requirements as far as which lenses their teleconverters can be used with, or what maximum aperture is required for autofocus.

True, it does require a 1-series body to be able to have autofocus at f/8, whereas all the others need f/5.6. That's just the nature of the beast, and one of the things you get for the price (and weight!) of these bodies. Everything is a trade-off.

You can always consider ebay-ing it, going with the 1.4x, or using a non-Canon brand 2x, which can sometimes allow autofocus on a non 1-series body (although you'll need to check this out, and how well it would work may also be an issue).

Good luck with your photography!

Nill Toulme · #6 September 19th, 2008, 06:03 AM

You'll get better results with the 1.4x anyway. The 2x usually has a fairly noticeable effect on image quality. It should only be used when absolutely necessary.

Nill

Doug Kerr · #7 September 19th, 2008, 06:20 AM

Hi, Richard,

Quote:

Originally Posted by Richard Rickard

Canon does not make 2.8 in a 500 or 600. And how would you handle a truck like that.
Using a 2 Xtc to get extra length with a 300mm 4/0 can not be done. Only short lens like a 70-200 2.8
makes sense or a 300 2.8, but then you have to spend a lot of money to do this.

"War is hell"
-Sherman

Best regards,

Doug