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Old Feb 23, 2005, 7:37 AM   #11
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20d-> better autofocus.. I'm going for the 20d
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Old Feb 23, 2005, 7:47 AM   #12
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I read the article Ponin referenced. Could someone please explain the following quote from that article:

"The EOS 20D provides full cross-type performance with maximum apertures as small as f5.6, yet it achieves up to 3 times the standard focusing precision when used with EF lenses featuring maximum apertures larger than or equal to f/2.8. The autofocus system of the Digital Rebel XT is inherited from the film Rebel XT body and has normal precision f5.6 sensors."

Thanx,Ron
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Old Feb 23, 2005, 8:18 AM   #13
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The 20D is worth the $500 difference (or more) if you require the differences that it has. It's up to you.

I made a post in anotherthread summarizing the main differences:

http://www.stevesforums.com/forums/v...mp;forum_id=37



Autofocus Differences:

There is a bit of a description of the higher precision autofocus in the 20D manual, page 68. You can download it in pdf form from the Canono site. Have to get to work tho ... otherwise I'd be able to summarize it ...



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Old Feb 23, 2005, 9:35 AM   #14
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BobA kind of nail it again: IMO the single most important feature of the 20D is its higher precision sensor (up to 3x times) for larger aperture lens of f/2.8 or more...

If you have f/2.8 lenses then the DRebel/XT/10D may have a harder time geting the DOF right... but on the other hand if you don't need the bokeh or use f/2.8 lenses then you are kind of 'throwing way' this 20D extra nice feature! :?
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Old Feb 23, 2005, 9:57 AM   #15
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OK, the quote in my post above has to do with autofocus, and a wider fstop will focus faster using the 20D? My main interest is macro, and focusing seems to be harder in macro anyway. So, if I use a macro lens set at f2.8, the 20D should be faster and more accurate? However, with macro, most people are going for more depth of field, so setting at 2.8 would not necessarily be desirable. besides, most wind up using manual focus trying to get the right area in focus.
I'm just thinking out loud people. I'm planning on getting a dslr in the spring, but the difference in price could help buy better glass. My wife has a Canon Rebel and 2 zoomes that will work on the Canon dslrs, so I'd just buy the body and a macro lens anyway. Well, maybe a tele extender too, and a 1 gig card, and a tripod, aaand I really don't have that much $ now...:shock:
Comments greatly appreciated.
Thanx,
Ron
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Old Feb 23, 2005, 11:48 AM   #16
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It's the max aperture that matters, not what you actually set it at.
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Old Feb 23, 2005, 12:06 PM   #17
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Ewok wrote:
Quote:
It's the max aperture that matters, not what you actually set it at.
Correct!
The camera always focus wide open and not at the aperture a picture is taken at...

... this is the reason why the AF is more accurate since the focused image has to fall within a narrower DOF as compared to smaller aperture where there'll be more 'slack' front to back as the result of the deeper DOF! :?
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Old Feb 23, 2005, 3:02 PM   #18
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OK guys,
I get it now. It makes perfect sense. :-):!:

Thanx,
Ron
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Old Feb 23, 2005, 4:14 PM   #19
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So your saying that the Rebel XT will focus fine with a 2.8 macro lens. . .just that the 20D will focus faster?
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Old Feb 23, 2005, 4:39 PM   #20
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The 20D will focus more accurately using the high-precision mode.
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