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09-10-2010, 11:56 AM   #1
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AF points....what are they?

So i finally think i need to figure this out Below are descriptions from amazon in regards to the AF points in camera:

Canon 5D mark 2 :
"A 9-point auto focus system is supported by 6 additional invisible Assist AF points, located inside the spot-metering circle to optimise subject tracking performance in AI SERVO AF mode. For accurate exposure readings in tricky lighting conditions, the spot metering circle covers just 3.5 percent of the frame. "

Nikon D700 :
"Nikonís Multi-CAM 3500FX autofocus sensor module features 51 AF points and the ability to use 3D tracking to focus and lock-on a moving subject"

Pentax k7:
"The K-7ís new SAFOX VIII Plus wide-frame autofocus system features 11 sensor points (with nine cross-type sensors positioned in the middle)"

Pentax k5? 18?

So ...um. I am not quite sure what they all mean. what do they do to begin with, and is more better? If this is the case, then why are some comparing speculated k5 with D700?

Thanks!

09-10-2010, 12:33 PM - 1 Like   #2
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If you've ever used an *istD, K10D, K20D, or K-7, the AF points are the little red dots that are superimposable on the focusing screen.

A focusing point is a point at which the AF system can measure the focus. The more, the better, as overall accuracy in auto and single-point mode can be improved. Currently, Pentax DSLRs have 11 focusing points. Since the K-5 will have 18, it's AF will both be faster, and more accurate.

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09-10-2010, 03:16 PM   #3
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Ah I see.

So in general, with K5 we should be up to par with 5D, but the Nikon system is still exponentially better with 51 points?

How much better is it when quantified to ..say, time?

For example, can we say that a D700 will be able to lock focus with something that is moving at 100km/hour in ...1 second flat.
A K5 will be able to lock focus to a similar object in...2 seconds.

Can we do that sort of quantifiable comparison?

Thanks
09-10-2010, 03:22 PM   #4
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AF speed also depends on what lens you're using (some have really long focusing throw, and SDM is slower than screwdrive), but it seems that the new Pentax AF system in the K-5 will be close, if not as good as, that of the competition. I would only expect a marginal difference between the K-5 and the 5D given that a lens with fast AF is being used (i.e. a DA limited or FA* lens).


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09-10-2010, 04:55 PM   #5
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One thing also is that it helps when the AF points are over the spots you use most often. Better yet if they are all cross type AF sensors.

There are cameras that are actually more faster/sensitive when using only the center AF point.
09-10-2010, 08:04 PM   #6
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ah cool thanks for the help guys
09-10-2010, 09:04 PM   #7
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Already got your answer but more AF points is better as it allows for more customisation as per the user's personal preferences.

bazz.
09-10-2010, 09:46 PM   #8
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QuoteOriginally posted by Adam Quote
AF speed also depends on what lens you're using (some have really long focusing throw, and SDM is slower than screwdrive), but it seems that the new Pentax AF system in the K-5 will be close, if not as good as, that of the competition. I would only expect a marginal difference between the K-5 and the 5D given that a lens with fast AF is being used (i.e. a DA limited or FA* lens).
They are also implemented in the K200d.

09-11-2010, 06:28 PM   #9
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While more AF points is better, it's not like twice as many as twice as good. After all, most of us here never use any but the center point anyhow. The advantage comes in mainly when you actually decide to select focus points, and then more means you can place focus more precisely. But it also takes longer select one from 50+ options than to select one from 11. For people who let the camera decide to focus, more points means the camera has more options to choose between. I don't see any particular reason to believe that this increase the likelihood of the camera guessing what what you had in mind, but nor do I think it would necessarily make it any less likely. Letting the camera select a focus point is asking for a lot of out-of-focus pictures no matter how many focus points the camera has available to choose between.
09-11-2010, 10:00 PM   #10
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Ah that makes sense I guess I have been doing this as well myself; the whole letting the camera choose always gets me the wrong points, so i ended up switching to middle and do it myself.
Not quite sure why the idea of a new camera makes me rethink my already working strategy
cheers

Last edited by D4rknezz; 09-11-2010 at 10:02 PM. Reason: elaborating
09-12-2010, 08:09 PM   #11
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Personally since I tend to shoot landscape and nature shots of objects that most of the time aren't moving around (non action shots) for me more auto focus points is nice but not really a huge factor. My old Olympus had three focus point and I rarely if ever found that I coudn't auto focus fairly quickly on one of those three spot and then re-compose my shot to how I wanted it. My K7 has all that I will ever need.

In fact with so many spot I sometimes have trouble in auto focus because the camera tries to focus on something that isn't the subject. So I generally prefer to have the auto focus locked on the center spot, position the spot over my subject to lock focus then move reconfigure the shot the way I want it to be.
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