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Old Sep 13, 2005, 8:23 PM   #1
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I've dont some searching for teleconverters here but most of the info I found is that alot of people have them. Not much info on good, bad, big, small......etc. I have an XT and a Sigma 70-300 APO DG and ofcourse want more reach with out spending $800 + right now. Not like I'm making a living doing this and my money tree isnt in bloom.

I've noticed most people have a 1.4 or a 2.0. (ofcourse my eye is on the 2.0). I have also read that with the 2.0, you need to adjust 2 stops. Is this a major issue? I'm not sure what else I'm trying to ask here, just looking for more info on teleconverters. Not just "ya, I have those in my bag". Is one better than the other? Why would I want a 1.4 when I can have a 2.0? Buy Canon, Sigma.......??

thanks for any input. :?

the other lenses I have are the Canon 18-55 (kit lens) and Canon 38-76 (had for a few years).
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Old Sep 13, 2005, 8:32 PM   #2
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I would say that in general you want to match your teleconverter brand to the lens brand, though many people would disagree. And, yes, they reduce the amount of light reaching the sensor by a stop or 2. So, you'll have to increase ISO or decrease shutter speedto getthe same exposure as without it.

Like a lens or filter, buy the best quality you can comfortably afford, if the quality of the teleconverter is only so-so and your lens is wonderful, then you're wasting a lot of the lens' potential.
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Old Sep 13, 2005, 9:19 PM   #3
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overkill wrote:
... Is one better than the other? Why would I want a 1.4 when I can have a 2.0? Buy Canon, Sigma.......??

thanks for any input. :?
The 1.4x is usually better since it doesn't degrade a lens as much as a 2x...

However you're running into 2 issues:
1. You'll lose the autofocus if your lens is slower than f/5.6 which the 70-300 APO DG is
2. A matched teleconvereter is only designed to 'match' certain set of lenses and my guess is the Sigma won't work on your lens (ditto with the Canon) - Theses teleconverters have more correcting elements in them than regular TCs and protrude inside the rear of the lens mount: http://www.sigmaphoto.com/lenses/lenses_tele.asp

-> You're limited to generic (3-elements or less) teleconverters...

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Old Sep 13, 2005, 9:29 PM   #4
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Buy neither the Canon or the Sigma teleconverters:!:
They physically won't fit the lens in question.
The Canon & Sigma teleconverters are called matched teleconverters in that they will fit only certain lenses that can accept their front element protrusion.

Try a Tamron sp (the lower cost one) Teleconverter .
The lower cost one does not transmit its presence to the camera, so it will try (rather badly) to keep autofocusing.
If you get the higher priced one, it will inform the camera of the true new lens max F-stop which in the case of a 2x tc is now F11, and the camera will simply refuse to even try to focus (Canon has a cut off at F5.6 in the cameras bios).

The viewfinder will also be quite dark at the F8 with a 1.4x tc or F11 with a 2.0x tc.

It will work, I used to try to use the tamron sp 2.0 tc on my old EF 100-300 F5.6.

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