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Old Jun 8, 2005, 5:27 PM   #11
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wsandman1 wrote:
I just got a Sigma 18 - 200 DC lense.
I have one question for anyoneowning this Lense. What's the largest apeture your camera show at maximum zoom? The specs say 6.3 but the camera says 5.6. I have a 20D with the latest firmware updates. The rep at the camera store said that this was okay. It showed the same 5.6 reading on the 20D at the store. Is it possible that the lense is defective? I have 4 days to return it.
I see you never got the answer to your question. Sigma designs these lenses to report to the camera a maximum aperture of F5.6. That's because the 10d, 300D, 350D, and 20D cameras shut off autofocus for a lens slower than F5.6. Because Canon cameras are somewhat over-engineered, they will actually autofocus all the way to F9 that I know of (you need pretty good light with that slow a lens, though).

This "little white lie" that the lens tells the camera is not a problem, nor is it a defect. Since the actual light getting through is what determines exposure, this misinformation has no detrimental effect on exposure at all. I have a Sigma 50-500mm F6.3--it works the same way and in fact will still autofocus with the Tamron 1.4x converter, which makes the Bigma/Tamron combo an effective F9. As far as the camera knows, though, it is still a 500mm F5.6.

I've tested this with a 300D, 350D, and 20D. It is no problemo!

Bill (not you...another Bill)
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Old Jun 9, 2005, 9:39 PM   #12
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You could sell the 18-200 and 28-200 and use the money to buy a second camera body. Then you could use your two higher quality lenses without missing too many shots as well as having a back-up camera.
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Old Jun 10, 2005, 2:30 AM   #13
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Aaah - but this is what the Canon cheerleaders 'forgot' to tell you: The Tamron/Sigma 'digital' lenses will work on a full-frame/film camera (albeit not as optimum) - The EF-S with their shorter retro-focus are just expensive paper weights on a full-frame! :-) :lol: :G
Hee hee, not if your smart and buy L. :idea:

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