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08-12-2012, 12:28 AM   #1
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Af adjust

I found that on my K-5, I have to readjust the AF periodically. What stroke me is that these periods are getting shorter. In the beginning, a few months could do, now about each three weeks I have to readjust. I am only shooting with AF primes (mostly on tripod), so the AF is always screw-driven and thus mechanically.
I see the 'unadjusting' coming up by the slight softening of the photo's bit by bit. I check the pictures at 66% only, I think that 100% is absurd...
I also found that there is, be it rather small, a difference between adjusting AF in LV and 'straight'.
I am using the SpiderLenscal and carefully set up the camera for parallelism, and shoot tethered with Eye-Fy on my Macbook to check instantly the adjustments (not the rear LCD thus).
Did anybody over here made the same observation?


Last edited by philippe; 08-12-2012 at 09:16 AM.
08-12-2012, 12:50 AM   #2
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Could be one (or more) of the 3 spring-loaded screws holding the actual AF sensor underneath the mirror box is/are coming loose. This can happen when they weren't threadlocked sufficiently. When this happens, the lens will indicate the focus (by AF) is farther than it actually is.
08-12-2012, 10:16 AM   #3
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Your shouldn't be judging the sharpness at 66%.
If 100% doesn't work for you, then use 50%
At 66% it's hard for your computer to represent image pixels with screen pixels due to rounding errors--so your images may in fact be perfectly sharp.
08-12-2012, 10:22 AM   #4
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I'm sending my K-5 to Pentax this week for that reason. I had noticed some time ago ago that I just wasn't getting the sharpness I was used to, especially with my Da* 50-135mm. So, for the first time, I tested some lenses using various AF fine tuning settings, and discovered that images were much better at a setting of +10 (the maximum adjustment without hacking the firmware). It wasn't guesswork - the difference was easy to see.
2 weeks later, noticing the focus problem had come back back, I retested under pretty identical settings, and found that setting AF tuning back to zero was better. My 2-year warranty expires in November, so I will let Pentax take a look at it.

Note - my testing may not have been as precise as yours, but I did use mirror-up, remote, 1 stop down from max aperture, 3 shots at each AF adjustment, forcing the lens to refocus for each shot.

08-14-2012, 05:42 AM   #5
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I just spoke with a Benelux Pentax Agency service technician.
He states that it is normal that the adjustments are getting out periodically.
"...There is always a normal shifting of the tolerances due to use, this is not wear. If one is using any kind of gear, adjustments are always under stress and by this getting out of order, more or less..."
He said that: "...AF should be checked and, if needed, adjusted each two months. Even a slight knock or a sudden shake can cause issues. Transporting the camera bag for instance on the back of a bicycle, is the worst that can happen to a camera, and most of the time the origin of that kind troubles..."
He warned to always put the camera bag on a seat, in the car, and to attach it with the seatbelt, do not put it in the trunk or on the floor.
The same can happen to lenses too: "...wether it be SDM or screw driven, vibrations and intensive shakes are evil..."
He ended: "The more one uses a camera [and lenses], the more one has to check the adjustments..."

Hearing this, I think that a good camera bag and reasonable attention are essential!
08-14-2012, 12:39 PM   #6
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QuoteOriginally posted by philippe Quote
I just spoke with a Benelux Pentax Agency service technician.
He states that it is normal that the adjustments are getting out periodically.
"...There is always a normal shifting of the tolerances due to use, this is not wear. If one is using any kind of gear, adjustments are always under stress and by this getting out of order, more or less..."
He said that: "...AF should be checked and, if needed, adjusted each two months. Even a slight knock or a sudden shake can cause issues. Transporting the camera bag for instance on the back of a bicycle, is the worst that can happen to a camera, and most of the time the origin of that kind troubles..."
He warned to always put the camera bag on a seat, in the car, and to attach it with the seatbelt, do not put it in the trunk or on the floor.
The same can happen to lenses too: "...wether it be SDM or screw driven, vibrations and intensive shakes are evil..."
He ended: "The more one uses a camera [and lenses], the more one has to check the adjustments..."
Tell me this was a joke?! After repairing my own Ds & K-m (and also Limited lenses), I noticed the threadlock Pentax were using must be really expensive because they were almost always not sufficient and resulted in loose screws.
08-15-2012, 02:55 AM   #7
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QuoteOriginally posted by wlachan Quote
Tell me this was a joke?! After repairing my own Ds & K-m (and also Limited lenses), I noticed the threadlock Pentax were using must be really expensive because they were almost always not sufficient and resulted in loose screws.
No, it's not a joke, why would it be?
I know the man, it's a serious craftsman with a long state of service, he's servicing Lieca too (trained in Solms) and formerly serviced Nikon (before the digital age)...
BTW, that 'loosening' happened to my Linhof Large Format camera too when I was hauling it around on power plants. I remember the problems I had due to the vibrations caused by the heavy machinery. I had to check and readjust the brass on Dural swallow fittings for the camera movements every night I came home. The same happened to my Hasselblad after a rough time on a construction site, the hook retaining the mirror had to be adjusted... The only camera that never caused that kind of problems was my Technorama 617, but this one is so primitively built that almost nothing can go wrong, besides the film transport mechanism, but that's exceptional...
Perhaps, just perhaps, here we can see the difference in price between a camera purposely constructed for rough professional use and the K-5, its a just guess...
10-12-2012, 07:47 PM   #8
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AF adjust under different light

I thought my AF on my K5 was going in and out, too, but now I'm starting to think that it has to do with the light. I've read in other places that under tungsten a wide aperture lens will back focus... It is easy enough to set up the AF in the shade, and set it up under a somewhat dim tungsten light. The difference is dramatic and consistent: -6 in tungsten, +4 in shade, and about 0 in bright sun. Do other cameras and other brands have the same problem? (I saw a similar effect on my K100D super with the same 50mm f1.4).

By the way, it is the light during focus, not exposure, so even if you're using a flash, if the camera focused under tungsten, it will have the negative bias.


Last edited by gpellegrinetti; 10-12-2012 at 07:50 PM. Reason: (forgot to mention the flash effect)
10-13-2012, 04:03 AM   #9
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QuoteOriginally posted by gpellegrinetti Quote
Do other cameras and other brands have the same problem?
I know little about other models from other brands, but the K-5 definitely has an issue with light colour temperature in low light.
The K-30's and K-5 II's AF systems have been redesigned to combat this K-5 weakness.

QuoteOriginally posted by philippe Quote
"...There is always a normal shifting of the tolerances due to use, this is not wear. If one is using any kind of gear, adjustments are always under stress and by this getting out of order, more or less..."
I guess this makes sense to some extent but shouldn't cause AF microadjustments from 0 to +10 and back. Any drastic changes like these, AFAIC, are either down to something being loose mechanically or a measurement issue (which could have to do with different light colour temperatures).
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