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03-13-2008, 09:49 AM   #1
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Cross type AF and aperture

I know alot of other manufacturers specify that their cross type AF points only work at certain apertures or better (f/2.8 normally) Does anyone know if pentax's system has a similar restriction? I've never seen it mentioned, and pentax has more cross type sensors that its comparable competition.

03-13-2008, 04:43 PM   #2
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QuoteOriginally posted by Geekybiker Quote
Does anyone know if pentax's system has a similar restriction?
it is not a restriction - it is an advantage to have additional sensors that can work better
with brighter lenses
03-14-2008, 02:23 PM   #3
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QuoteOriginally posted by deejjjaaaa Quote
it is not a restriction - it is an advantage to have additional sensors that can work better
with brighter lenses
Ummm sensors that won't work below a certain aperture certainly is a restriction. Unrestricted would be operating at apertures. However google isn't turning up any info on it.
03-14-2008, 02:39 PM   #4
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QuoteOriginally posted by Geekybiker Quote
Ummm sensors that won't work below a certain aperture certainly is a restriction. Unrestricted would be operating at apertures. However google isn't turning up any info on it.
the way they do this is to provide additional (not instead) sensors that work when you put lenses that are typically F/2.8 or better...

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

you can read it all (better) or just skip to the last page

03-14-2008, 04:10 PM   #5
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QuoteOriginally posted by Geekybiker Quote
Ummm sensors that won't work below a certain aperture certainly is a restriction. Unrestricted would be operating at apertures. However google isn't turning up any info on it.
Most cameras won't focus properly with apertures smaller than f5.6. That's standard. As they said, what they offer are adittional extra-sensitive AF sensors that can work with a little less light, and faster in good light.
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