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02-22-2014, 09:31 AM   #1
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Does anbybody know how the AF system picks a focus point?

I have been playing with the AF on my K-5iis and I can't figure out how the camera chooses a focus point when it's set to 5 or 11 points. It almost seems to be random. Does anybody know what the algorithm is?


Last edited by maxxxx; 02-22-2014 at 01:46 PM.
02-22-2014, 09:41 AM   #2
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I think this is the main reason we use centre point or select focus point. I just have my DSLR set to select point and have learned to do it fairly quickly, without looking at the commands.
The auto select.. meh, Id use it only when I wouldn't know where the subject will appear. I hope someone can give you an answer, but I doubt anyone outside Pentax can help with it
02-22-2014, 10:48 AM   #3
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It picks the closest point with reasonable contrast, as far as I can tell.

Regards,
--Anders.
02-22-2014, 10:54 AM   #4
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asp1880 has it. Most cameras of any brand will pick the closest point with good contrast. I'm with Na Horuk. I use only the centre point on my K10D. That way I know where it is focusing. I have also recently set my camera to focus only with the AF button rather than the shutter release. I don't have the fumble problem when focusing on point A and then recomposing while trying to hold the shutter button just so.

02-22-2014, 11:24 AM   #5
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QuoteOriginally posted by Canada_Rockies Quote
asp1880 has it. Most cameras of any brand will pick the closest point with good contrast. I'm with Na Horuk. I use only the centre point on my K10D. That way I know where it is focusing. I have also recently set my camera to focus only with the AF button rather than the shutter release. I don't have the fumble problem when focusing on point A and then recomposing while trying to hold the shutter button just so.
I generally use center point focus too and I also use only the AF button (I think they call it back button focus). The reason why I tried the 11 point focus is that I want to take pictures of my dog playing with a ball. She moves around a lot so it's hard to keep her always in the middle of the frame. I can't really figure out how the focus tracking behaves to make the process more predictable.

---------- Post added 02-22-14 at 10:25 AM ----------

QuoteOriginally posted by asp1880 Quote
It picks the closest point with reasonable contrast, as far as I can tell.

Regards,
--Anders.

That makes sense. That spot is not necessarily the expected spot :-(.
02-22-2014, 11:26 AM   #6
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QuoteOriginally posted by maxxxx Quote
Does anbybody how the AF system picks a focus point?
That's an easy one... it's the point that your least likely to want in focus, a sixth sense kinda thing.
02-22-2014, 11:31 AM   #7
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My understanding is that first point to acquire focus wins.

As with those who posted above, I generally use a fixed point (usually center) for AF-S. For tracking in AF-C...I haven't a clue. AF-C sucks on my K10D and I never use it


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02-22-2014, 11:49 AM   #8
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QuoteOriginally posted by Kerrowdown Quote
That's an easy one... it's the point that your least likely to want in focus, a sixth sense kinda thing.
That's exactly what I have observed!

02-22-2014, 12:00 PM   #9
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QuoteOriginally posted by stevebrot Quote
My understanding is that first point to acquire focus wins.

As with those who posted above, I generally use a fixed point (usually center) for AF-S. For tracking in AF-C...I haven't a clue. AF-C sucks on my K10D and I never use it


Steve
My K10D works perfectly, and tracks focus on Formula 1 race cars coming directly at the camera with no problems at all. As long as they are being pushed into the pit by the crew.
02-22-2014, 12:04 PM   #10
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QuoteOriginally posted by Canada_Rockies Quote
As long as they are being pushed into the pit by the crew
Ouch, that's sounding a tad cynical.

Even if it is true.
02-22-2014, 12:09 PM   #11
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QuoteOriginally posted by Canada_Rockies Quote
My K10D works perfectly, and tracks focus on Formula 1 race cars coming directly at the camera with no problems at all. As long as they are being pushed into the pit by the crew.
Mine is about the same. One reason I seldom use the feature is that the noise of the frantic whirring of the AF motor sets all the neighborhood dogs to howling. Not good.


Steve
02-22-2014, 12:32 PM   #12
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QuoteOriginally posted by stevebrot Quote
Mine is about the same. One reason I seldom use the feature is that the noise of the frantic whirring of the AF motor sets all the neighborhood dogs to howling. Not good.


Steve
You would't have the noise problem at Formula 1 though.
02-22-2014, 01:04 PM   #13
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The real question is how do you pick the focus point? After all, you do know where you want the subject in the frame, don't you?
02-22-2014, 01:04 PM   #14
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QuoteOriginally posted by maxxxx Quote
You would't have the noise problem at Formula 1 though.
True, though if I had to wait until all the cars are being pushed...


Steve
02-22-2014, 01:14 PM   #15
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QuoteOriginally posted by DSims Quote
The real question is how do you pick the focus point? After all, you do know where you want the subject in the frame, don't you?
I know the focus point I want but with a dog that's playing and running it's quite hard to compose a picture. I am just trying to figure the camera's behavior so hopefully I can adjust to that.
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