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07-24-2011, 07:52 AM   #1
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Bad/wierd K5 focus issue

The photo below is if the bottom of my Vizio television. When I'm bored, sitting on my bed, fiddling with my various lenses, one of the things I'll often do is zoom in, focus on, and snap a photo of the silver grill with all its holes. Last night I tried that with my K5, and it would rarely if ever achieve focus. Ditto this morning, with additional light coming through the window.

Probably five times out of ten the lens will twitch and the camera will indicate focus lock, but its so blurry that you can barely tell there are circles. That's in the viewfinder even. It's not even close to appearing in focus. Two times the lens will hunt a bit then the camera will indicate focus lock, but the image will be that blurry. Two times the lens will hunt a bit and the camera will indicate it can't lock focus. The remaining try it may achieve focus lock or it may twitch and indicate it can't. If I swing the lens to the DTV logo, or up to the black edge of the screen, the camera locks perfectly, so it's the camera having trouble with the grill. The thing is, my K-10D locks focus every single time with every lens. It has no trouble with the grill at all.

I have tried this and it's repeatable with a Tamron 70-300, Tamron 70-200 2.8, Tamron 28-80, Sigma 18-50 2.8, and the Pentax kit lens. In all instances I was close enough that the grill filled the viewfinder, but far enough that I was well into the focusing range of the lens. Lighting in the room is above my head, about seven feet from the tv grill, and is four 100 watt (equivalent) fluorescent bulbs, plus (this morning) sunlight coming through the window. The K-10d will focus with only one bulb in, so I don't think available light is contributing to the issue.

I'm aware of the notes in the manual about certain surfaces being hard to achieve focus on, but I'm shocked that this could be one of them, especially when it's so easy for the K10.

Can anyone else try to duplicate this so I can confirm whether it's an issue with my camera or the K5 in general?

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07-24-2011, 08:03 AM   #2
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I haven't experienced this but a couple of times, or it would concern me too. The few times I have, were shortly before the battery went totally dead. Is your battery fully charged?
Generally, I find lithium batteries to retain almost full useful power until they just stop....as in my power tools...I can be drilling just fine in a hard surface with no seeming loss in power and it will just stop instantly, so this baffles me when it has happened in my K5? But on a full charge, I have never encountered this focus problem, so in my case I have to assume it is battery related?

Have you been having trouble in outside shooting or in situations other than your TV shooting?

Best Regards!
07-24-2011, 08:15 AM   #3
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My battery is fully charged, I just took it off the charger an hour before I was playing with the camera. Also, I forgot to mention, I have focusing set to the center point.

To your other question, I can't say that I'm entirely satisfied with the percentage of shots I get that are in good focus, and there are a few times that I've had the camera hunt and fail to lock outdoors when I questioned why, but nothing repeatable. For all the disappointments I've had, I've also gotten some stunningly sharp photos, and as I adjust to the K5 the number of sharp photos are starting to rise again.

This, it just shocks me that it's so bad and so repeatable. I hope it's my camera alone.

Oh, let me add one other focusing issue I've had. I have a Tamron 2X Pz-AF BBAR MC7 teleconverter. It works and achieves focus lock on my K10 with both the Sigma 18-50 2.8 and the Tamron 70-200 2.8, although not always perfectly with the latter. On the K5 with this teleconverter and these lenses, I experience a similar thing, the camera refuses to focus. The lenses will, at best, sit there and twitch. Subject and lighting do not matter.

Last edited by KyPainter; 07-24-2011 at 08:24 AM.
07-24-2011, 08:35 AM   #4
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What version of firmware are you running? The AF on the K10 is completely different from the K5.



07-24-2011, 08:41 AM   #5
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What you may be encountering is one of the unfortunate limitations of the K-5 AF system in low light.
The K-5 can be overconfident with its low light focusing accuracy, frequently 'locking on' to a subject wildly front-focused. This occurs with me also, but only in low light. At times, even reengaging focus doesn't end up getting the camera to focus properly, which is a shame. I'd rather the K-5 just admit defeat than confidently front focus on me. This has been happening with me from firmware v1.02 to the current v1.11
07-24-2011, 09:06 AM   #6
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While I can't imagine it's something as simple as this, I have to ask, do you have your AF assist lamp turned on?

I was at a wedding last night with my K-5 and while I'm sure I missed a handful of shots, the rest were well focused, even into the evening when there was barely any natural light coming in through the windows. To make matters worse, they had very little lighting over the dance floor apart from the "disco" style crawling dots that spin around the room.

I was also concerned about AF in this situation, but my K-5 came through.
07-24-2011, 09:37 AM   #7
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I'm using firmware 1.03. Autofocus assist light is enabled, but there's more than enough light to keep it from coming on. I just tried unscrewing bulbs and with the light from the window it doesn't come on unless I've unscrewed all four bulbs. At that point, even with the assist light, it won't focus lock even on the DTV logo. With one bulb still screwed in, the assist light not coming on, it will still lock on the DTV logo every time. With all bulbs on (400w) and the curtain completely open to increase available light to the max, the camera still won't lock focus on the grill. It's definitely not light level related, at least I can focus on and take sharp photos of other subjects in the room with no problems.

As annoying and disappointing as this is, even if it is a camera shortcoming, I can live with it since the focus is so far off it can't be mistaken for an in focus shot. What does worry me is whether this exists to a lesser degree in other circumstances and might explain the greater number of out of focus shots I get with the K5.
07-24-2011, 10:09 AM   #8
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Indeed, that's my issue with the K-5 also - in that the 'low-light' situations where focusing is slightly off occurs when the AF assist lamp is either not activated due to just enough light for the K-5 to focus without it, or when the AF assist lamp is useless (e.g. night landscapes). Quick shifting usually fixes this problem, but only for DA lenses, of which I only currently have two (12-24 and 55-300). Just wish it didn't have to require that. Would be good for accurate AF if it's going to lock on, otherwise MF is the only other option.

07-24-2011, 05:05 PM   #9
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Have you tried Live View?

If I recall correctly, use of Live View can help overcome focusing issues in low light. It's worth a try anyway. Not that this is the ultimate solution as most folks don't want to use live view at times. But it might be interesting to see if Live View eliminates this reproducible issue.
07-24-2011, 05:15 PM   #10
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Could you try two things.

1. Try a fixed white balance (not Auto).

And...

2. Turn the camera between 15-60 degrees while attempting focus lock.

I don't have a k5 yet, but I read this section a lot, and I've been curious for a while if these actions could make a difference.

Thanks...
07-24-2011, 06:16 PM   #11
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Well, I fiddled with this a bit more today.

First off, live view focuses usably, but not perfectly.

Second, it's absolutely not low light related, because I packed the tv out on the deck into the direct sunlight and the camera still would not focus on the grill.

Third, rotating the camera 90 degrees does improve the camera's ability to achieve focus lock by a factor of 2-3. I don't understand why it would, because it's still just a grill of holes no matter which way you view it. Perhaps the direction of the light is changing relative to the camera?

Fourth, I have a set of computer speakers with fronts that are also a silver grill with round holes. The holes are about 1/4 the diameter of the holes in the tv grill. The camera will achieve focus lock each and every time, same position, same light, same everything. This suggests to me that there's something unique or unusual about this pattern of holes that really messes with the camera.

Fifth, I switched the camera to AFC and Auto focus point select and tried focusing on the grill. Oddly enough, the camera greatly favors the focus points on its power switch side. Even if I rotate the camera 90-180 degrees to change what part of the grill the points see, or the direction of the lighting relative to them, the same focus points keep lighting up.

Lastly, I did find one advantage to the extremely poor focusing here. With the camera in AFC I could move it around over this grill of holes and, by bringing it near the DTV logo or an edge, I could see exactly where the focus points became effective. The moment the DTV logo started to come within the center circle of the viewfinder from the left or right, focus instantly snapped in. It would snap in just outside the circle coming from the top or bottom.
07-24-2011, 06:36 PM   #12
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It ought to be pretty clear by now that you just need to get a new TV
07-24-2011, 06:40 PM   #13
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QuoteOriginally posted by bxf Quote
It ought to be pretty clear by now that you just need to get a new TV
Yeah, that's for sure, but if I replace it I have to replace all the other things I test focus on and end up dissatisfied. That's not so bad for most things but I've got so many bad test pictures of my toes, how do I replace those?
07-24-2011, 07:51 PM   #14
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It's The Pattern

QuoteOriginally posted by KyPainter Quote
The photo below is if the bottom of my Vizio television. When I'm bored, sitting on my bed, fiddling with my various lenses, one of the things I'll often do is zoom in, focus on, and snap a photo of the silver grill with all its holes. Last night I tried that with my K5, and it would rarely if ever achieve focus. Ditto this morning, with additional light coming through the window.

Probably five times out of ten the lens will twitch and the camera will indicate focus lock, but its so blurry that you can barely tell there are circles. That's in the viewfinder even. It's not even close to appearing in focus. Two times the lens will hunt a bit then the camera will indicate focus lock, but the image will be that blurry. Two times the lens will hunt a bit and the camera will indicate it can't lock focus. The remaining try it may achieve focus lock or it may twitch and indicate it can't. If I swing the lens to the DTV logo, or up to the black edge of the screen, the camera locks perfectly, so it's the camera having trouble with the grill. The thing is, my K-10D locks focus every single time with every lens. It has no trouble with the grill at all.

I have tried this and it's repeatable with a Tamron 70-300, Tamron 70-200 2.8, Tamron 28-80, Sigma 18-50 2.8, and the Pentax kit lens. In all instances I was close enough that the grill filled the viewfinder, but far enough that I was well into the focusing range of the lens. Lighting in the room is above my head, about seven feet from the tv grill, and is four 100 watt (equivalent) fluorescent bulbs, plus (this morning) sunlight coming through the window. The K-10d will focus with only one bulb in, so I don't think available light is contributing to the issue.

I'm aware of the notes in the manual about certain surfaces being hard to achieve focus on, but I'm shocked that this could be one of them, especially when it's so easy for the K10.

Can anyone else try to duplicate this so I can confirm whether it's an issue with my camera or the K5 in general?
Regular or repeating patterns confuse autofocus systems, particularly phase detect systems. Th AF system splits the same image area into two images of opposite phase and then compares them as the focus changes, but the repeating patterns all look the same whether they are in phase or not, so the system may stop the lens in the wrong position, hunt, or even lock correctly depending upon the pattern size, lens magnification, distance to the subject, and so on.

Nikon discusses this in their manuals, Pentax isn't so helpful.

Ray
07-26-2011, 06:12 PM   #15
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These are all hypotheses, not facts:

*I think the reason why rotating the camera works "better" is because the auto-focus system might be catching some of that non-grill area and it's helping with focusing.

*With the grill with the bigger holes, you might just have enough difference between dark/light for the AF system to lock.

This is why in these kinds of situations I would focus on the split between the black bezel and the grill. They're on the same plane so it should work well.

Have you tried zooming in to the point where the TV's grill occupies most of the frame?
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