Cross type AF and aperture

Geekybiker · 03-13-2008, 09:49 AM

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.

deejjjaaaa · 03-13-2008, 04:43 PM

Originally posted by Geekybiker

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

Geekybiker · 03-14-2008, 02:23 PM

Originally posted by deejjjaaaa

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.

deejjjaaaa · 03-14-2008, 02:39 PM

Originally posted by Geekybiker

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

ricardobeat · 03-14-2008, 04:10 PM

Originally posted by Geekybiker

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.

03-13-2008, 09:49 AM	#1
Geekybiker Veteran Member Join Date: Feb 2008 Location: Chicagoland Posts: 337	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.

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03-13-2008, 04:43 PM	#2
deejjjaaaa Veteran Member Join Date: May 2007 Location: steel city / rust belt Posts: 2,043	Originally posted by Geekybiker 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
Geekybiker Veteran Member Join Date: Feb 2008 Location: Chicagoland Posts: 337 Original Poster	Originally posted by deejjjaaaa 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
deejjjaaaa Veteran Member Join Date: May 2007 Location: steel city / rust belt Posts: 2,043	Originally posted by Geekybiker 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
ricardobeat Veteran Member Join Date: Aug 2007 Location: Brazil Posts: 376	Originally posted by Geekybiker 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.