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06-15-2011, 06:37 AM   #1
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Area AF: How does the camera choose?

This thread might belong elsewhere since it pertains to more cameras than just the K-5, but since I just got a K-5 and since I'm weary from looking around for an answer to this one, I'm taking the easy way:

Probably a very basic question: Can anyone explain to me how the camera chooses the AF point from the 11-point AF matrix? I've always used center point, plan to do some experimenting with area AF on my new K-5 ... but I would like to know what the camera's criteria are for choosing a focus point if it's not centered so I'll have some hope of interpreting the results.

I do have the feeling this is answered elsewhere here on the Forums, but I couldn't find anything. Thanks.

06-15-2011, 06:45 AM   #2
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It typically goes for the closest subject, which is useful to know when using AF-C on fast moving subjects (E.G bird in flight photography) with a featureless background - though once the background becomes more contrasty and textured I would recommend selecting the AF point myself because the camera will be confused when it comes to distinguishing detailed foregrounds from backgrounds.
06-15-2011, 07:03 AM - 1 Like   #3
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If you half press the shutter button, the camera will choose another focus point. You can use this mode to cycle thru potential subjects, however, if your camera doesn't have a confirmation light, you're either guessing or relying on your superior visual acuity to judge whether you've hit your target.
06-15-2011, 11:53 AM   #4
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QuoteOriginally posted by dragonfly Quote
If you half press the shutter button, the camera will choose another focus point. You can use this mode to cycle thru potential subjects, however, if your camera doesn't have a confirmation light, you're either guessing or relying on your superior visual acuity to judge whether you've hit your target.
I guess I learned something new. I had no clue it did that. It won't do that with the AF button will it?

Repped!

06-15-2011, 12:09 PM   #5
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QuoteOriginally posted by Digitalis Quote
It typically goes for the closest subject, which is useful to know when using AF-C on fast moving subjects (E.G bird in flight photography) with a featureless background - though once the background becomes more contrasty and textured I would recommend selecting the AF point myself because the camera will be confused when it comes to distinguishing detailed foregrounds from backgrounds.
Just a quick question, without trying to steal this thread:

Are you going to get better results using area AF for BIF vs. point AF?
With the K5, I find that point AF works just fine ... for me.

Cheers.

JP
06-15-2011, 12:59 PM   #6
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The designers can either choose to prioritize
A. signal strength (more contrasty points are favoured),
B. point position (central points are favoured), or
C. proximity (closer points are favoured).

My unscientific feeling about this is that the Pentax system weights the factors in the above mentioned order. I've experimented by aiming at a uniformly textured, slanted surface to see if I could make it pick the closest point. But it really wants to pick the center point.

Sincerely,
--Anders.
06-20-2011, 04:58 AM   #7
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QuoteOriginally posted by jpzk Quote
Just a quick question, without trying to steal this thread:

Are you going to get better results using area AF for BIF vs. point AF?
With the K5, I find that point AF works just fine ... for me.

Cheers.

JP
Center point works fine if you'r good a aiming I try to set the camera to 5 or 11 point AF for bif against a clear sky. That way the camera automatically pics the bird (since there is nothing else to focus on). With 1 spot af I sometimes miss the bird, and AF hunts out to infinity. I hope that made it clear
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