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01-14-2013, 07:30 AM   #1
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K-5 Front Focus Woes

Ok I know this has been discussed to death. I don't know what I want to do with my problem though. Here goes. I've consistently noticed less hits on my k-5 in low light. This is much more noticeable with my 50mm lenses at apertures wider than 2.8. This is using the AF for focus confirmation on manual lenses, which I realize is somewhat dodgy. So I've been toying with this cheap pentax kit zoom and found that it misfocused as well, especially under lower light and tungsten. In daylight moving between -10 to 0 on the AF adjustment menu didn't seem to do much. In more middle light (5-6 EV or so) I can see it moving over a sequence of shots. I do notice that there is some inconsistency in lower light with a definite failure rate. This seems higher under tungsten. Moving to -10 globally seems to fix all of my focusing issues under tungsten and I can happily use the AF system down to 1EV give or take as long as I have something with contrast to grab. I do realize that the center point is as large as the spot mark. Sooo....after a great deal of trying to test with inconsistent results I threw my camera on a tripod and used a calender to show the plane of focus and offset the camera 30 degrees. Sure enough, -10 was giving me consistent results with both the 18-55, the fa 28-80 kit, as well as my manual 50mm. Moving it up made everything front focus. I never had that many issues with my k-7 and focus except in horrible light, so it made me wonder why I keep missing so much with an AF system that is supposedly improved. I upgraded the firmware and didn't notice any improvement in low light, but in hindsight, I do feel like the firmware changed some things. Just a feeling. It looks like it go beyond -10 just a hair. I wish I had an FA 50 to test with, but something doesn't seem right. I could upload some pictures if you wanted to see, but its clearly hitting more in a front focus position at 0. Usually I am stopped down to apertures where it wouldn't matter, but its frustrating to try to figure this out as I would like it to be in tune, but lack the fast AF lenses I would need to test more. I'm thinking to debug mode it and step it back a hair and then dial it in from there. I have my k-7 as a backup, but I would hate to send in a body that I could just calibrate to my satisfaction in a matter of 20 minutes. What do you all think? Is it normal to sometimes get a body that is out of calibration in regards to AF? Don't they test that sort of thing in the factory? I don't get it.

01-14-2013, 07:36 AM   #2
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Hmm...thinking I will leave at -10 for a while until I get a proper setup to test focus calibration with a ruler and proper target.....not scientific enough for my liking yet. I was just really wondering who else had this experience. -10 seems like a good bit to be out of step.
01-14-2013, 10:32 AM   #3
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I am having some AF inconsistencies of my own, though it's appears to be specific to wide angle focal lengths and all my tests have been in bright, natural light for the sake of having a more controlled test.

I can appreciate wanting to fix a problem on your own if it only means spending twenty minutes with a test chart; I've done it myself with a few lenses over the course of two or three years. However, to have a body that is apparently so far out of alignment that you're maxing out the AF Fine Adjustment is unacceptable to me. You have a K-7 backup body so it doesn't sound like you simply sell off your old DSLRs once you're done with them. Nevertheless, imagine you sold the K-5 a year or two from now. I couldn't sell a camera in the condition you described. I'd be giving somebody else the same headache I had.

If the K-5 is still under warranty my recommendation is to send it in to CRIS and have them work their magic. Even if the warranty is past I would send it in. Getting the camera back in pristine working order will be a welcome surprise and you can use it without the memories of having to use it in such a jerry-rigged fashion.
01-14-2013, 10:45 AM   #4
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Seems to me like the PDAF isn't performing as it should. Some have perfectly fine K-5's and the handful I tried were bad. In the end I had it swapped with a K-30 and haven't experienced same problems since.

01-14-2013, 04:11 PM   #5
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Im going to build a focus rig and see what it does in sunlight first. Its almost like it is focus shifting under lower light.
01-14-2013, 04:14 PM   #6
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Its still under warranty. I just dont want to give it up for some weeks. I have a k7 for backup, but i would rather be sure i have a problem. There is nothing else wrong with it. All pentax is going to do anyways is recalibrate it. Im ok doing that myself. :-)
01-14-2013, 04:27 PM   #7
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One of the better methods I found to test AF involved using different colors. You could create an image at your monitors resolution with 10 or so thin bars, each with different colors from the visible spectrum and then one by one focus on each bar - you might notice, some colors affect the AF more than others. Red was worst in my case.

Here's the same thing basically but performed in a slightly different way: The colors are illuminating from my monitor: https://www.pentaxforums.com/forums/general-technical-troubleshooting/191214-...ml#post2013534
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