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03-03-2008, 10:41 AM   #1
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Aperture and AF speed?

Just curious, does the max lens aperture change the AF speed of the camera? I know pentax gets a little slow in low light, so wondering if going from f/3.5 kit to a f/2.8 lens would improve that.

03-03-2008, 10:53 AM   #2
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It does change the AF speed , since the smaller aperture doesn't allow as much light to reach the AF sensor. The difference is almost nothing in bright light, but in low light, a lens with an opening of 1.4 will be quite a bit faster to focus than one with an opening of only 5.6.
03-03-2008, 11:11 AM   #3
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nice document talking about principles of AF (Phase Comparison AF) systems :

http://doug.kerr.home.att.net/pumpkin/Split_Prism.pdf
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