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Old Mar 11, 2005, 8:22 PM   #1
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Hi guys, I know the 20D fires off 5FPS and the XT only 3 but how well does the AF work with a fast lens- does the AF of the XT allow for rapid firing of say "racing motorcycles or flying birds".....how much improved is the AF on the 20D as opposed to the 10D? Is it much slower than the 1D series?

Thanks everyone- just some questions that left me puzzled.
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Old Mar 11, 2005, 9:27 PM   #2
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In DSLRs, the lens is the most important component of the whole system. I have never used a 10D, so can't compare the focus speed of that camera vs that of the 20D using the same lens, however, from what I have read, lenses vary a lot in focus speed, even on the same camera.

Careful with the term "fast lens". In the context of your question, a fast lens is one that focuses quickly. The more common useage of that term deals with arpature size (or f-stop).

The 20D is an amazing camera that starts up quickly and focuses smartly with the lenses I own, but I'm sure that a lens that has a slow focus motor won't perform as well on any camera. The 20D's ability to snap off 5 frames a second is amazing, though I'll readily admit I seldom use the capability because of the way I use my camera. Those who shoot a lot of sports, or even children running around, will be able to take better advantage of that capability. It's kind of like having the ability to go from 0-60MPH in 4 seconds... I may never use it, but it's nice to have the capability if I want to use it.
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Old Mar 12, 2005, 12:01 AM   #3
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i have the xt (butthe rebel when i took this picture)and this lens (not the greatest but better than the kit lens)


and took this pic (resized and compressed but not cropped)

if you want the .tif lemme know and i can host it.
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Old Mar 12, 2005, 8:15 AM   #4
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There are 3 aspects to autofocus that are relevant I think:

1. The accuracy of the system in the body. The 1 series have 45 point AF, the 20D has a 9 point, and the XT 7 point system. The more expensive cameras have more AF points and better AF algorithms.

2. The 20D has one high-precision AF point in the centre which allows large aperture (f2.8 or better) lenses to focus more accurately. The 1 series have this too, but the XT does not.

3. The focus speed of the lens comes in 3 varieties, ring USM - fastest, USM - fast, non-USM - slower.

So for sports or flying birds with the more expensive lenses then yes the 20D will likely perform noticably better than the XT.
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