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Old Sep 15, 2005, 7:28 PM   #1
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So I'm reading this in the canon EF Lens chart:

"If the EF 70-200mm f/2.8L USM lens is attached to an EOS camera having
multiple focusing points and an Extender is attached to the lens, only the
center focusing point will be usable for AF."

Now, does this mean that the 70-200 USM is subject to this and NOT the 70-200 IS?

Oddly enough it is notated in the 70-200 IS column, but it clearly seems to be referrring to the non IS version, or am I wrong? Does it apply to both?
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Old Sep 15, 2005, 7:52 PM   #2
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The IS(Image Stabilization) and USM(UltraSonicMotor) really have nothing much to do with the focusing. One stabilizes unsteady hands, and the other carries out the instructions from the AutoFocusing module in the camera.

Exactly backwards :-)
All focusing points are, or can be use all the time with or without the extender. (At least as far as I know, I 've never heard of a TC restricting you to the center focusing point, so I may be wrong) Depending on which focusing points you select.

It depends on the camera you are using it on but for the

20D
- with an F2.8 lens the center focusing point becomes a high precision focusing point
- with an extender the aperture drops, and the center focusing point becomes just a plain one like all the other.
- camera will attempt to focus with lenses down to F5.6

RebelXT
- all focusing points are standard,
- camera will attempt to focus with lenses down to F5.6

1D series
- more high precision focusing points and work with smaller apertures than F2.8.
- cameras will attempt to focus with lenses down to F8 (I believe)

Peter.
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Old Sep 15, 2005, 8:21 PM   #3
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PeterP wrote:
Quote:
The IS(Image Stabilization) and USM(UltraSonicMotor) really have nothing much to do with the focusing. One stabilizes unsteady hands, and the other carries out the instructions from the AutoFocusing module in the camera.

Exactly backwards :-)
All focusing points are, or can be use all the time with or without the extender. (At least as far as I know, I 've never heard of a TC restricting you to the center focusing point, so I may be wrong) Depending on which focusing points you select.

It depends on the camera you are using it on but for the

20D
- with an F2.8 lens the center focusing point becomes a high precision focusing point
- with an extender the aperture drops, and the center focusing point becomes just a plain one like all the other.
- camera will attempt to focus with lenses down to F5.6

RebelXT
- all focusing points are standard,
- camera will attempt to focus with lenses down to F5.6

1D series
- more high precision focusing points and work with smaller apertures than F2.8.
- cameras will attempt to focus with lenses down to F8 (I believe)

Peter.
Yes, other than the USM generally makes focus a bit quicker and quieter. But I realize that as far as IS it is not related, that is why I was a bit confused by the note in Canon's lens chart. I currently have a 20D and I was wondering if anyone here has had an experience with this phenomenon mentioned by Canon before I off and buy one or the other.
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Old Sep 15, 2005, 10:18 PM   #4
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Take a look at this: http://www.pbase.com/fstopjojo/image/49303910/original
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Old Sep 15, 2005, 10:28 PM   #5
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Now that's pushing the envelope...
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Old Sep 15, 2005, 11:12 PM   #6
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That is kinda like this shot of mine:

http://esmith.marx7.org/galleries/Mo..._hawk_owl1.jpg
This was taken with the 20D + 600mm f4 + 1.4xTC + 1.4xTC + small extention tube + 2xTC. The extention tube is required for this combo to work. I'm rather surprised how well it came out and if it hadn't be a really amazingly bright day it wouldn't have worked.

Eric
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Old Sep 16, 2005, 12:25 AM   #7
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Excellent stuff, Eric. Now THAT's pushing the envelope...
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Old Sep 16, 2005, 12:33 AM   #8
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Woah, are you seriously telling me that was a 3763mm shot!?
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Old Sep 16, 2005, 8:08 PM   #9
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eXterme telephoto :-)

Back to original question.
I tried my Sigma 120-300 F2.8 with and without a 2x teleconverter and all the focusing points worked in both cases.
So I would suspect they would also work with both the Canon 70-200's and a teleconverter.

Peter.
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Old Sep 16, 2005, 8:16 PM   #10
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Thanks Peter, exactly what I was wondering.
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