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Old Sep 5, 2010, 1:06 PM   #1
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Default Problems with my K7 Autofocus.

I noticed while taking photo's the other day at Disney, that my camera would refuse to lock focus on many of the normal contrast scenes. At home today I experimented with my camera, and found it won't lock focus when the focal length is set anywhere under 28mm about 80% of the time. If I zoom into 30 and above it seems fine. My lens is the DA 18-55mm WR. I also have the DA 55-300, and that works fine at any focal length. So is my problem in the lens or body? Strange thing is it seems to work indoors in artificial light. Go figure.
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Old Sep 5, 2010, 1:37 PM   #2
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That does sound strange. I do know that any camera will have trouble focusing if there's not some contrast (light/dark) no matter how bright the lighting.

I sometimes have had trouble getting the 12-24 to focus on something that's at infinity. Its been better with the K7 than it was with the K20. To deal with it, I either change the camera to manual focus and set it on infinity or else move the camera slightly, which often gets it to lock focus. You might try those with your kit lens. I've never used the 18-55 on the K7, tomorrow I'll pull it out and try it to see if mine does the same thing.
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Old Sep 5, 2010, 2:37 PM   #3
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Hi Tony,

I would usually say that this sounds like a lens problem, but with it working in artificial light, it sounds like it could possibly be connected to the tungsten sensitivity shift in the AF sensor. This is a unique aspect of the K-7, so it's relatively unexplored territory for the great majority of the DSLR experience. I'd call Pentax support, try to talk to a real tech specialist, and see if you can send it in for a fast track checkup. I would think they'd want to find out if this can be a problem with new feature in the AF system.

I don't shoot much really wide, and when I do, there's usually a very close object to focus on, and I've never experienced an inability to lock in daylight with any of my bodies. It's possible, considering Harriet's experience, that there might be something of a problem with the AF system locking on very small-sized contrast borders.

One thing to realize with any AF issue, is that the AF system works best with contrast borders which intersect the AF sensors at a right angle to the orientation of the sensor's lines. It's helpful to know where these lines are actually located, and a member at DPR posted a very good map of the sensor lines recently:

http://forums.dpreview.com/forums/re...ssage=36211521

The contrast borders don't have to be perpendicular to the sensor lines, but if the camera is struggling to lock focus, I'll sometimes tilt the camera to give it a more optimally oriented contrast border to work with.

I'd check the AF again, using this additional information, to eliminate any possible user error before contacting Pentax tech support, but if even this doesn't help, then I'd be giving them a call.





Scott
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Old Sep 5, 2010, 3:58 PM   #4
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Quote:
Originally Posted by mtngal View Post
That does sound strange. I do know that any camera will have trouble focusing if there's not some contrast (light/dark) no matter how bright the lighting.

I sometimes have had trouble getting the 12-24 to focus on something that's at infinity. Its been better with the K7 than it was with the K20. To deal with it, I either change the camera to manual focus and set it on infinity or else move the camera slightly, which often gets it to lock focus. You might try those with your kit lens. I've never used the 18-55 on the K7, tomorrow I'll pull it out and try it to see if mine does the same thing.
Thanks. I would appreaciate that. Seems to work fine 30mm and above. Is there a reset on the camera? Wonder if somethings just not screwed up in memory
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Old Sep 5, 2010, 4:43 PM   #5
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Hi Tony,

One more thought -- have you upgraded the firmware to the latest? If not, it would be worth a try, if you already have but have never noticed the problem before, then a reinstall might be worth a try.

Also, AF problems can be exaggerated by low battery charge. If your battery wasn't fully charged during the first instance, I'd try recreating the situation as closely as possible with a fully charged battery. There are a whole lot of variables to consider.

Scott
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Old Sep 6, 2010, 10:22 AM   #6
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There is definitely a problem. If I have it set to dull wide angle it won't lock focus, if I change the focal length to about 30mm pointed in the same place it will lock focus. I'm wondering if the infinity calibration on the lens is off though. It seems to always happen on infinity. The lens tries to keep moving closer to infinity, but can't. I'll give Pentax a call tomorrow. This is very aggravating.
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Old Sep 7, 2010, 10:38 AM   #7
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Your lens may be front focusing. If it's a problem at infinity, have you tried to manually focus at infinity with the problem focal lengths? Because the lens has a clutch for the focus mechanism, you can manually focus even when the camera is set to AF. If you can't, then there's something wrong with the lens (something has come loose in the focus mechanism). If you can, then perhaps it's front focusing with the camera - my 12-24 significantly front focused with the K7. I could see it when I finally got around to shooting some focus charts (that's harder to do with a wide angle lens). The AF adjustment was able to correct it without problems.

Any word from Pentax yet?
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Old Sep 7, 2010, 12:30 PM   #8
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Originally Posted by mtngal View Post
Your lens may be front focusing. If it's a problem at infinity, have you tried to manually focus at infinity with the problem focal lengths? Because the lens has a clutch for the focus mechanism, you can manually focus even when the camera is set to AF. If you can't, then there's something wrong with the lens (something has come loose in the focus mechanism). If you can, then perhaps it's front focusing with the camera - my 12-24 significantly front focused with the K7. I could see it when I finally got around to shooting some focus charts (that's harder to do with a wide angle lens). The AF adjustment was able to correct it without problems.

Any word from Pentax yet?
Yes, I just called Pentax, and spoke with Mark. He seems to think there is no problem. He said that I shooting scenes without enough contrast. Can you do me a favor, and try shooting against an old wooden fence about 20 feet away at 18mm, and tell me if your having issues. You might also try shooting into a bunch of tree's, just make sure your shooing at infinity, and at 18 mm. Here is one of the Disney scenes I was having trouble with. These shots actually did focus, but only after recomposing them.
Attached Images
  

Last edited by tony3dd; Sep 7, 2010 at 1:05 PM.
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Old Sep 7, 2010, 3:54 PM   #9
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I was recently having a similar issue with my K10D backup camera that I have had since it was new. It would not lock focus 95% of the time when using any lens that was wider than about 28-30mm and I wasn't getting the red focus square on my older manual lenses no matter what the focal length. On zoom lenses I could zoom in, focus and then zoom out and shoot.

I called Pentax and at first they told me that it was a normal scene contrast issue and nothing could be done, but when I mentioned that every one of these lenses worked perfectly if I put them on my K20D and tried to shot the same scene they suggested I send it in. Unfortunately my camera is long out of warranty, but they adjusted the focus, cleaned the camera and it works beautifully now.

Steve
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Old Sep 7, 2010, 11:28 PM   #10
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I put the kit lens on the K7 to play with it in good light tomorrow. I played around with it inside, but in rooms that don't have a lot of light. I could see the AF assist light come on and help lock focus - that's the first time I've seen that (I don't usually take pictures in such low light) and I thought that was very cool. I had no trouble locking focus on stuff at a number of various distances, including about 30 feet away. That was far enough to get the lens to show infinity, but all of this was in low light and much of the time I could see the focus assist light. It wouldn't lock focus when pointed at the middle of the stainless steel refrigerator door, which I expected - no contrast. It would focus when pointed at a door with a window in it that was further away and in very, very low light. I'll play around some at lunchtime tomorrow. The marine layer is supposed to be in so it will be very diffused, grey light not bright sunshine. That shouldn't make all that much difference.
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