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10-31-2012, 04:18 PM   #1
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K-5 II AF sensor size

There I was, already to pull the trigger and buy a K-5 when I bumped into some threads on the size of the AF points.
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The basic jist of the thread being that the size of the autofocus crosses are much larger then the viewfinder displays such that if you attempt to focus on say a models eye or a squirrel in a tree the cross is so large the camera may lock focus on the ear, or a nearby branch, etc.

So my question is... has anyone tested the AF point size on the new k5 ii? Easy test is to hang a coat hanger on a white wall, select center focus point (or any single point I suppose) then slowly move corner of the hanger into the frame to see when you get focus lock.

Thanks all for the help. I learn so much here as a lurker its not even funny.

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10-31-2012, 04:25 PM   #2
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The new AF system seemed to behave just like the old one in the original K-5 with respect to AF point size, but I didn't really do an extensive test of this. With the new select area expansion feature, however, you'll be able to keep the camera focused at a certain distance even if the subject moves over to another AF point, which could come in handy for what you're describing.

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10-31-2012, 04:34 PM   #3
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QuoteOriginally posted by Big_Bang Quote
There I was, already to pull the trigger and buy a K-5 when I bumped into some threads on the size of the AF points.
HTML Code:
 https://www.pentaxforums.com/forums/pentax-k-5/177572-all-fuss-about-auto-focus-point-size.html
The basic jist of the thread being that the size of the autofocus crosses are much larger then the viewfinder displays such that if you attempt to focus on say a models eye or a squirrel in a tree the cross is so large the camera may lock focus on the ear, or a nearby branch, etc.
Yes, the red square is a joke, the AF sensor is at least ten times the area of the red square. If you look through a K-5 viewfinder there's a faint circle a bit inside the black semi-circle lines; that seems to be where the A/F can lock on (anywhere in that circle).
10-31-2012, 04:45 PM   #4
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Most of my photo's are either landscapes at say f11, or indoor ambient light photo's of my kid at perhaps f2.8-f3.5. Its the indoor shots where I am concerned that the sensor will grab the background rather then his near eye. I could stop down some for added DOF, but then I either have to use a flash or up the ISO.... so accurate placement of autofocus is important for my shooting needs. AF tracking not so much so as I don't do sports or BIF.

10-31-2012, 04:51 PM   #5
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you can always manual focus, kick it old school!
10-31-2012, 05:12 PM - 1 Like   #6
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QuoteOriginally posted by Big_Bang Quote
I am concerned that the sensor will grab the background rather then his near eye.
Remember, camera AF cannot read your mind, no matter what the brand. In some scenes, if the AF sees several adjacent areas of contrast, or lack of contrast, it will have to choose what to lock onto. That may not always match up what you think the camera should be choosing.

AF always has issues, and those issues don't always relate to just AF point size. Unfortunately AF point size seems to be the current obsession around PentaxForums at the moment, as if it is all that matters with AF working properly or not. Pic related, from Nikon:

10-31-2012, 05:14 PM   #7
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The AF points have been that size since at least the K10D. Somehow people have managed to take pictures with their Pentax cameras anyway...
10-31-2012, 05:26 PM   #8
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No doubt about that.... obviously lots of love for the K-5! It seems the general work around for the K-5 is to stop down a little and focus on the face rather then the eye. Or manual focus, or live focus as necessary. All this advice is great, particularly rawr's nikon autofocus chart.

Has it been determined then that the Af sensor size is the same for the k-5II(s) as the K-5?

10-31-2012, 06:00 PM   #9
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QuoteOriginally posted by Big_Bang Quote
Has it been determined then that the Af sensor size is the same for the k-5II(s) as the K-5?
No one has systematically tested even the K-5 or the K-5II's 'AF point size' that I know of (yet?).

But look at the nice test done by UnknownVT of the good AF 'point size' sensitivity of the K-x eg using centre-spot AF. The K-5 in my experience is capable of precision better or equal to any of that, at pretty much all AF points.
10-31-2012, 08:01 PM   #10
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QuoteOriginally posted by rawr Quote
Thanks RAWR, that's a very fascinating read indeed. I wonder if anyone has ever done similar back of the napkin analysis on non-Pentax cameras, and if not.... why not.
10-31-2012, 08:07 PM   #11
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I don't think that the current AF area size is a huge problem. Smaller AF areas can help with better targeting small features, but in practice, I've been fine with all my shallow DOF shots.

There is a possibility that the new f/2.8 AF area is a bit smaller. Maybe not, I guess no one has looked into this yet.

Too bad that the K-5 II review did not investigate the new AF module further than establishing that it manages to lock focus in light levels lower than the K-5 can deal with.
10-31-2012, 10:38 PM   #12
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QuoteOriginally posted by Big_Bang Quote
I wonder if anyone has ever done similar back of the napkin analysis on non-Pentax cameras
I'm sure some folks have - eg this guy with his Canon 7D - and possibly others have done similar. But these sort of tests are hard to find. Maybe a good Google search will find some more, but I haven't tried.

TBH as a centre-spot, focus-recompose kind of guy, the whole issue is not hugely interesting to me. You don't need to play with AF so much for most shots in order to get decent results if your technique is OK. And most of the time I even have the AF indicators on screen turned off on my K-5. All those flashing lights are simply distracting.

Needless to say, I also never turn the AF confirmation beep on. I also never enable the K-5's AF illumination light.

Last edited by rawr; 10-31-2012 at 10:50 PM.
11-01-2012, 09:45 AM   #13
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QuoteOriginally posted by ElJamoquio Quote
If you look through a K-5 viewfinder there's a faint circle a bit inside the black semi-circle lines
OMG i would never have found about this one if you didnt mention it !
and yes doing a quick test, it focuses when something enters that circle ! which is bigger than the red square, not 10 times though...
11-01-2012, 12:46 PM   #14
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QuoteOriginally posted by obscura Quote
OMG i would never have found about this one if you didnt mention it !
and yes doing a quick test, it focuses when something enters that circle ! which is bigger than the red square, not 10 times though...
10 times in area. You don't think that circle diameter is over 3x the width of the red square?
11-01-2012, 01:00 PM - 1 Like   #15
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Back with my K7, the focusing point was a bit off center. I did a few tests to see where the camera thought it was supposed to focus.
The image shows the focus points slightly below where they should be. But I believe their sizes and general locations have not changed... other than being properly aligned in most current Pentax cameras, of course. :-)

Note the blue + is the center focus spot, and it overlaps with the center top & bottom focus points.

http://moringello.com/photo/focusing_1.jpg

(dunno why the image would not insert... anyway, hopefully the link is good. It should be viewable by all).
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