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07-21-2012, 05:09 PM   #1
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Yet Another AF Failure From My K-5



I used Auto-AF (11 points) and AF-S in this image. The lens was Sigma 30mm f/1.4.

I think the K-5 thought the red-shirt man in the left-back was more interesting than the man just in front of itself. (Face blurred over request).

So what do you think?

07-21-2012, 05:11 PM   #2
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User error imo. Focus and re-compose? Manual focus?
07-21-2012, 05:14 PM   #3
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No re-compose. I don't focus and re-compose, I choose a relevant focusing point if necessary. And as I said, I used Auto-AF (11 points) and AF-S in this image. That means I used AF.
07-21-2012, 05:15 PM   #4
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QuoteOriginally posted by Crosshair Quote
No re-compose. I don't focus and re-compose, I choose a relevant focusing point if necessary. And as I said, I used Auto-AF (11 points) and AF-S in this image. That means I used AF.
He was giving suggestions as to how to avoid those problems in the future. It's obvious the AF system locked on to the point of highest contrast, the guy with the red shirt.

07-21-2012, 05:18 PM   #5
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Center point helps a lot. Focus and recompose too.
07-21-2012, 05:18 PM   #6
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Oh if so, I must apologize @creampuff. Sorry I took it the wrong way
07-21-2012, 05:20 PM   #7
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Mental note: K-5 with Sigma 30mm combo has difficulty focusing on hairy chested guys...
Joking of course.

07-21-2012, 05:24 PM   #8
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so I thought that the Auto-AF option would focus on the nearest object of contrast. or it was the same in nikon anyway. I produced that way with the nikon d90 in the time.

the k-5 chooses the point of highest contrast in the frame, disregarding its position. is that so?
07-21-2012, 05:26 PM   #9
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@creampuff well I must say I thought those hairs made up a contrast against the cream color but as you pointed out the k-5 disregarded it.
07-21-2012, 05:31 PM   #10
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Such is life with AF
07-21-2012, 05:43 PM   #11
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Do you have the red dots turned on? Because then you would at least see the focus point the camera is using.
07-21-2012, 05:46 PM   #12
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Yeah, I had them turned on and as fas as I can remember, two points in the center (over the face and upper chest) were used. If side ones were used I'd notice right away and re-take the shot. So bad I didn't stoop to zoom-in and check the focus. Seemed OK in the instant preview so I moved on.
07-21-2012, 05:50 PM   #13
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If I'm not mistaken, the center AF sensor is a lot bigger then the red dot or the central circle of the standard focussing screen might suggest. It is entirely possilbe that the right shoulder/upper arm of the guy in the red shirt and the face and helmet of the intended target were both within the crosshairs (pun intended) of the AF sensor. If that is the case the sensor would select the area of highest contrast as the focus point, It is a contrast detect Auto focus method after all.

It may be that the error is one of misunderstanding how the AF function works.

Last edited by wizofoz; 07-21-2012 at 05:51 PM. Reason: clarity
07-21-2012, 05:54 PM   #14
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@wizofoz yeah, your suggestion makes sense. the central focusing area extending and overlapping the red guy in the back. so it is proof that the k-5 disregards distance in focusing and looks for the highest contrast on Auto-AF or Single-AF around which point is selected.
07-21-2012, 05:59 PM   #15
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All of the focus points are much larger than indicated. Auto-11 is a crap shoot at best. Imo, it's basically telling the camera "read my mind" about what to focus on. It is a much more reliable technique to either dial in an AF point to use, or use the center one and recompose as needed.
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