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Old Feb 13, 2012, 4:26 PM   #1
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Default Multi point AF what is it used for?

HI all

could someone explain the use of AF area 23 or 11 or 5 vs 1. I don't understand the use of so many Auto Focus points if the camera chooses what to focus on instead of you. Or is this used for action shots where something is always moving Like a bird or a car or something like that?

Could you help me understand what it is used for?

Thanks
Mark
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Old Feb 13, 2012, 6:26 PM   #2
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Multi point AF helps if you are photographing a fast moving subject like a BIF, athlete running, vehicle moving....AF is 'on' .
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Old Feb 13, 2012, 7:15 PM   #3
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Lesmore beat me to it, but I was going to say exactly what he said.
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Old Feb 13, 2012, 7:32 PM   #4
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Is 11 point AF more suited than 5 point AF. for what type of situations?

Thanks
for your previous response that makes sense
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Old Feb 14, 2012, 4:25 PM   #5
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Quote:
Originally Posted by popellis View Post
Is 11 point AF more suited than 5 point AF. for what type of situations?

Thanks
for your previous response that makes sense
I'm not technical expert...but I would think having 11 AF points as opposed to 5 AF points would be better...more areas to focus on his subject.
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Old Feb 14, 2012, 10:37 PM   #6
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Quote:
Originally Posted by popellis View Post
Is 11 point AF more suited than 5 point AF. for what type of situations?

Thanks
for your previous response that makes sense
Hi Mark,

5 point gives a more selective focus area than 11 point, a diamond shaped pattern in the center of the focus screen (the center point + those directly above, below and to either side). Let's say that you're trying to shoot a bird in flight, and it's relatively small compared to the whole VF. By limiting the AF sensors to the middle of the VF, you'd still have a fairly large area of active focus points, but it's less likely that a high contrast border like a telephone pole at either edge of the frame could confuse the AF system to focus on it instead of the bird.

Multi point AF tries to focus first on the closest object that has sufficient contrast borders regardless of where this object might be in the frame. By using the 11 point version, you're telling the camera that it can use close to the full viewfinder area. this is useful for very quick moving subjects, where you might have trouble keeping up with its motion. 5 point is more discreet, and can be used for slower subjects, or if you feel confident that you can keep the subject centered. Single point is the most discreet, but takes the most skill to use with moving subjects.

I'll offer a few more tips about the AF system used by Pentax, and I hope that you don't mind. . .

The AF sensor areas are actually much larger than the AF "points" most people talk about. The Center focus area roughly covers the central ( ) etchings on the VF, and though the surrounding areas are smaller, they're only slightly so, and more oval shaped.

Any contrast border within the active area can be "chosen" by the AF system, and those that have either higher contrast or are more closely aligned with either the vertical or horizontal axes can be preferred by the AF system, even though they may not be part of the main subject. The AF system cannot read you mind, so the photographer must be the one who decides if the AF system has chosen the correct focal plane, and then trip the shutter.

Scott
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Old Feb 15, 2012, 7:11 AM   #7
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Thank you Scott

That was a great explanation, I'm sure there are others who are confused about this as much as I am. That makes a lot of sense now.
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