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09-18-2014, 08:47 AM   #1
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more AF points - always better, or ?

It struck me recently that more AF points could just catch more extraneous items and not necessarily be ideal for many users. If you stepped up to the K-3 you would be the right people to ask! Has anyone using a large set of active AF points noticed this? I know a lot of people switch to center point and recompose, or pick a strategic subset, so perhaps many owners choose not to use the full set of points anyway - but this information would be helpful. More technology may not be always better for imagers.

Thanks!

09-18-2014, 08:51 AM   #2
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With the K-3 there's no real drawback since the points are just in a more dense layout within the same space.

One advantage of cameras with more points and larger frame coverage is that they can do a better job of predicting of what you're trying to focus on. On the other hand, the AF can fail you in auto mode if you're trying to pinpoint a single target, which is why users normally switch to single-point/group AF modes in those scenarios.

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09-18-2014, 08:58 AM   #3
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Depends on the AF system and your needs. If you need a lot of AF points near the centre for AF tracking, then its good. If you need points spread out, then a dense configuration might not help at all. For my purposes, the Pentax AF system is enough, and I can always switch to live view to focus anywhere I want, if need be
09-18-2014, 09:10 AM - 1 Like   #4
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I have never understood how multiple point AF works. Do people just trust the camera to pick what they would like their focus to be? I like to tell the camera where I would like the focal plane. I always use single point.

I would think one would really need to understand how the AF system uses information form the various AF points for the camera to "decide" where to put the focus. Wil it pick the closest object? The closest object near the center of the frame? Or the focal plane that gets the most AF point hits? If one knows how the system works, THEN maybe more points is helpful. Otherwise, you may as well roll the dice.

09-18-2014, 09:12 AM   #5
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One lesser but useful note about more points: it means that the center point covers a smaller area. That means when you need center point to focus on a certain point (say the eyes in a portrait), the focus is more precise. I definitely notice this if I'm using a narrow depth of field on a portrait that isn't straight on. Also more points leads to better tracking focus because the camera has more points to interpolate subject movement.
09-18-2014, 09:18 AM   #6
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QuoteOriginally posted by Adam Quote
With the K-3 there's no real drawback since the points are just in a more dense layout within the same space.

One advantage of cameras with more points and larger frame coverage is that they can do a better job of predicting of what you're trying to focus on. On the other hand, the AF can fail you in auto mode if you're trying to pinpoint a single target, which is why users normally switch to single-point/group AF modes in those scenarios.
Does this also apply to tracking in AF-C? In other words, 27 points in the same zone as 11 points won't lose track as easily? On my K-30, I've tried Select Point and Enhanced AF, and it works when I move the camera to recompose, but doesn't track moving subjects very well.
09-18-2014, 09:26 AM   #7
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As in many things the K-s1 is a 'tweener - it has AF Hold and Enhanced AF but fewer points. I expect I will bump AF Hold up & see how it helps when moving objects inevitably hit the larger gaps.
09-18-2014, 11:03 AM   #8
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QuoteOriginally posted by Lukinosity Quote
I have never understood how multiple point AF works. Do people just trust the camera to pick what they would like their focus to be? I like to tell the camera where I would like the focal plane. I always use single point.

I would think one would really need to understand how the AF system uses information form the various AF points for the camera to "decide" where to put the focus. Wil it pick the closest object? The closest object near the center of the frame? Or the focal plane that gets the most AF point hits? If one knows how the system works, THEN maybe more points is helpful. Otherwise, you may as well roll the dice.
What you're describing is what in Pentax world is called AF-A. As you said for the most part you dont really know what the camera will choose in this mode, however that isn't the only use of a camera with many AF points.

My most recent pentax was K-x which has pretty bad / simplistic AF-C, so I can only chime in on how I use predictive AF with 39 points on D600 / D7k (AF-C-3D in Nikon)

I usually always start with center point, I put my subject in center, and hold down AF. As my subject moves across the frame and closer / farther from me, the AF point moves and it's smart enough to know what was previously in the center (usually in my case a person's face) and keeps that object in focus as it changes distance and location in the frame. I dont have to recompose to keep the subject under only that one point.

I know there are other uses for it, but this is the way I use it. On my stress test I can track my son running towards me and get 85% keeper rate of his face in focus (yes most of it is crap, but one or two of them usually have a nice expression I wouldn't get otherwise)

So no, you're not necessarily playing dice, you're still in control, only your tool is a bit smarter now.


Last edited by Andi Lo; 09-18-2014 at 11:12 AM.
09-18-2014, 12:22 PM   #9
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QuoteOriginally posted by Adam Quote
With the K-3 there's no real drawback since the points are just in a more dense layout within the same space.
What he said. Assuming that you have a great deal of processor power, having more data is better than less for doing a valid evaluation.

QuoteOriginally posted by Na Horuk Quote
Depends on the AF system and your needs.
Indeed! I shoot primarily using center point only for a number of reasons. Now, if I were shooting Nikon, I might opt for using the full array. The blinking lights in the viewfinder are more fun than watching a cluster of fireflys!


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09-18-2014, 12:50 PM   #10
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The more information and calculation power the better the predictions, additional information well-handled is never bad for a system.
09-18-2014, 01:57 PM   #11
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QuoteOriginally posted by VisualDarkness Quote
The more information and calculation power the better the predictions, additional information well-handled is never bad for a system.
The 'well-handled' part was my concern; if any points strayed near the edge I'd be likely to capture too many random items. Not that I don't compose the whole image of course! If one lets automation rule unrestrained, one gets what one deserves.
09-18-2014, 02:03 PM   #12
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QuoteOriginally posted by jimr-pdx Quote
The 'well-handled' part was my concern; if any points strayed near the edge I'd be likely to capture too many random items. Not that I don't compose the whole image of course! If one lets automation rule unrestrained, one gets what one deserves.
It's all a matter of good calculations and prioritizing, the human mind is pretty simple to predict to a good degree in many situations and I'm pretty sure that photo compositions is one of them.

---------- Post added 09-18-14 at 11:05 PM ----------

If you get enough points, good enough distance measurements and low errors you gan basically "paint" the whole scene for the AF.
09-18-2014, 02:23 PM   #13
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My Canon 5DMK3 has 61 AF points. In addition to the advantage of better tracking moving things, I find the broad dispersion extremely handy for shooting macro and close-up shots. In Canon systems, many of the focus points have within, smaller more pinpoint AF points. These are great for macro. Instead of manually focusing in LiveView, I'm retraining myself to plop a macro AF point on my desired target and trust that. 61 points allows that target to be almost anywhere within the frame.

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09-18-2014, 08:48 PM   #14
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QuoteOriginally posted by Andi Lo Quote
My most recent pentax was K-x which has pretty bad / simplistic AF-C, so I can only chime in on how I use predictive AF with 39 points on D600 / D7k (AF-C-3D in Nikon)

I usually always start with center point, I put my subject in center, and hold down AF. As my subject moves across the frame and closer / farther from me, the AF point moves and it's smart enough to know what was previously in the center (usually in my case a person's face) and keeps that object in focus as it changes distance and location in the frame. I dont have to recompose to keep the subject under only that one point.
If I'm not mistaken, the Expanded Area AF feature in the K-30, K-50, K-5 II(s), and K-3 works the same way. The K-3 is better in this regard because it has an 86k pixel RGB metering sensor with Real-Time Scene Analysis.

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