[greg_77]

So, do we know which of the AF sensors are the f2.8 ones?

If you let the camera choose which AF sensor to use will it alway use the f2.8 ones if you have a fast lens mounted, or will it use any of them?

Thanks - Greg

[obscura]

it has one f/2.8 af point, its the one in the center.
check this post
https://www.pentaxforums.com/forums/pentax-dslr-discussion/198596-k-5-ii-f-2...ml#post2134365

if it works the way i think it does, i dont think its an easy, or even possible task, to built 2.8 af points which are not in the center...
maybe if the points where smaller they could built 2.8 af like this
 ---
| + |
 ---

but all cramped up in the center...

[greg_77]

it has one f/2.8 af point, its the one in the center.
check this post
https://www.pentaxforums.com/forums/pentax-dslr-discussion/198596-k-5-ii-f-2...ml#post2134365

if it works the way i think it does, i dont think its an easy, or even possible task, to built 2.8 af points which are not in the center...
maybe if the points where smaller they could built 2.8 af like this
 ---
| + |
 ---

but all cramped up in the center...

Thanks for the link. I thought there were more than one. Makes it easy to select the hi-precision one I guess.

I dont think f2.8 sensors have to be in the center. I'm pretty sure Canon or Nikon have more than one on their high end cameras.

Cheers - Greg

[obscura]

canon 5dmkiii which has more room because its FF has 61 points and only 5 of them are 2.8 crosstype all of which are located in the center in a vertical line
and after reading the 7d manual, it has one 2.8 af sensor in the center.(p91)

[RonHendriks1966]

Would it make sence to make f4 type AF sensors? Sine there are some fine lenses for that that don't have the advantage off the f2.8 crosstype sensors (like DA*60-250mm and DA*300mm).

[obscura]

i think 5dmkiii has some f/4 sensors but it wont make much difference...
i should also add that the k-5ii/s sensor is not 2.8 cross type it has vertical 5.6 and orizontal 2.8 only, and in theory thats not good at all (its kinda cheap)
7d is crosstype 2.8 both orizontal and vertical
and the 5dmkiii's 2.8 sensors are diagonal in addition to the standard (vertical horizontal) 5.6 crosstypes
but in practice the owners of k5ii/s are amazed by the focusing capabilities of their cameras, so i think it works better than expected...

[greg_77]

canon 5dmkiii which has more room because its FF has 61 points and only 5 of them are 2.8 crosstype all of which are located in the center in a vertical line
and after reading the 7d manual, it has one 2.8 af sensor in the center.(p91)

Interesting. Thanks.

Greg