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Old Sep 7, 2004, 6:14 PM   #1
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I've seen comments up on dpreview.com from people that indicates that the 20D has superior autofocusing than the 10D and that it's AF is 3x more accurate with lenses that have maximum apertures of 2.8 or less. That seems to be affirmed by this quote from Steve's review of a preproduction model of the 20D:

Quote:
The sophisticated 9-point autofocus system has a high-precision cross-type sensor in the center position. This new design seen for the first time in the 20D provides full cross- type performance with maximum apertures as small as f/5.6, 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.
I'm trying to understand why there is 3x greater AF precision with EF lenses with 2.8 or larger maximum apertures? What is this greater precision measured relative to? Is it relative to previous AF performance using EF lenses across all Canon bodies, or just relative to the 10D with those same EF lenses?

I'm trying to decide if it is worth retaining my pre-order for the 20D with the 17-85 EF-S IS lens, or if I should just buy the body and apply the $500 that would have gone to the 17-85 lens instead towards a faster EF lens...
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Old Sep 7, 2004, 10:06 PM   #2
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There's an FAQ to this very same question on the Minolta site:
http://konicaminolta.com/products/co...x7/ope01b.html


BTW I wouldn't be too fast on my feet... Chances are the 1st few cameras out of the line (just like cars) usually have a few bugs as kinks on the assembly lines are being ironed out (My early 10D for example had its serial# marked with felt tip pen which disappeared after a few days)
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Old Sep 7, 2004, 10:13 PM   #3
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Thanks, NHL!

That is a pointer to a great diagram explaining the theory behind this difference in behavior for faster lenses. So, the statements about greater precision are probably true for the 20D relative to the 10D because the latter didn't have any cross-type sensors. Am I getting this right?

Is there any reason why the same statement wouldn't also be true if there were EF-S lenses that were that fast?

Finally, do you have any advice with regard to my lens purchasing options?
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Old Sep 7, 2004, 10:24 PM   #4
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Actually the 10D had a cross hair sensor, but I don't think that sensor was designed for the camera, rather a carryover from their Elan film cameras...

May be there's some truth in theses front/back focus problems after all (My Sigma f/2.8 lenses have been behaving OK though under controlled tests) because of the larger defocus shift in faster lens! :?



Quote:
Finally, do you have any advice with regard to my lens purchasing options?
This is just my opinion: The Sigma 12-24 EX is the only full-frame zoom in this focal range so it's worth considering for the future... as for the 24-xxx f/2.8 lenses there's various choices one can buy from!
http://www.stevesforums.com/forums/v...648&forum_id=8
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Old Sep 8, 2004, 6:40 AM   #5
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I'm not sure what relavence this had however the 1D specifictions indicate the af sensors are different and 3x faster then those of the 10D. Is it possible that they were borrowed into the 20D design?
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Old Sep 8, 2004, 7:42 AM   #6
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If they did borrow part of the sensor from the 1D, that would be serious news.

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Old Sep 8, 2004, 8:37 AM   #7
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NHL wrote:
Quote:
BTW I wouldn't be too fast on my feet... Chances are the 1st few cameras out of the line (just like cars) usually have a few bugs as kinks on the assembly lines are being ironed out (My early 10D for example had its serial# marked with felt tip pen which disappeared after a few days)
Ahh, you edited this one after my first reply to it and I never saw this remark :roll:

Well, I probably wouldn't be so anxious to get the camera except I am going on a trip overseas in the beginning of October and would much rather be toting along a new 20D rather than the Oly C8080WZ that I currently have. I'm hoping for the best and keeping my fingers crossed! Of course, I may not even receive the camera in time so it could just be all academic anyways...
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Old Sep 8, 2004, 8:39 AM   #8
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mrkryz wrote:
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I'm not sure what relavence this had however the 1D specifictions indicate the af sensors are different and 3x faster then those of the 10D. Is it possible that they were borrowed into the 20D design?
Are the 1D sensors 3x more accurate too? Faster doesn't necessarily mean more accurate. Also, is the speed (and possible accuracy) only pertaining to lenses used with the 1D that have max apertures of f/2.8 or greater or is that restriction a bit more relaxed for the 1D?
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Old Sep 8, 2004, 8:42 AM   #9
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eric s wrote:
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If they did borrow part of the sensor from the 1D, that would be serious news.
I suppose it could be possible. It'd still mean the 20D was a downgraded offering compared to the 1D because I think it would only be the center sensor that is of the more accurate/faster type. Aren't the 1D sensors all of the same type?

How would we ever know if this were the case? Unless Canon actually told us, it would probably take someone dismantling the 20D and 1D to compare the components!
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Old Sep 8, 2004, 8:54 AM   #10
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IMO they can't pick and chose AF sensor(s)... It's an entire focusing module array designed specifically for each camera with its own splitting lenses in front for each phase detector

Also see the previous diagram, there's a difference between + and x sensors (the Minolta uses both). :idea:
http://konicaminolta.com/products/co...x7/ope01a.html
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