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09-19-2016, 07:28 AM - 1 Like   #1
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Focussing problem with my K-1 --> resolved!

I am shooting with the Pentax K-1 for one month now, coming from a Pentax K-5 IIs. It has been a mixed journey so far which probably has to do a lot with my own learning curve in mastering a full frame camera. But there are some other things that do not seem to be caused by my learning curve of this specific camera and one of them is the autofocus system.

I have noticed that when reviewing my photo's, there are surprisingly few photo's that are in focus. First I thought it was due too the shallow depth of field and hence my learning curve, but today I did some experiments on a tripod with newspaper and I found out that with f2.8 - f5.6/ISO 100, the autofocus system shows quite pronounced backfocus with the DFA 24-70. When I focus this lens manually in Liveview using focus peaking, it is a very sharp lens. But when I am using the viewfinder, the autofocus if often way off.

So I have used the auto focus fine tune option of the K-1, but had to go all the way to +10 to get the focus aligned with the centre focuspoint (I was using spot AF). Somehow it does not feel right to have such a major adjustment on a new lens and camera.

I will do some more testing coming weekend, also with other lenses, but what are your opinions and did you have to adjust your autofocus like this? And would this be a lens or a camera problem?


Last edited by Lampo; 12-13-2016 at 11:48 AM. Reason: Adjusted topic title
09-19-2016, 07:35 AM   #2
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The only lens I had to do that on was on a Sigma 100-300 f/4 that I traded off, and it took a +4. The rest of been spot on for me.
09-19-2016, 07:37 AM   #3
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QuoteOriginally posted by Lampo Quote
Somehow it does not feel right to have such a major adjustment on a new lens and camera.
The AF adjust is there to be used. I test all lenses on each camera before using them. As long as +10 gets you where you want then all is good. Now if ALL lenses were off +10 then I might consider sending the camera in for calibration. But not without extensive testing on a number of lenses.

Also keep in mind that unless your testing process is meticulous you really are just guessing. Tests need to be done 5 to 10 times repeatedly under strictly controlled conditions. Just the movement caused by your finger on the shutter button can skew the test.
09-19-2016, 07:52 AM   #4
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Thanks for the replies, with the K-5 IIs I also did not have to adjust the focus, not even with the DA 300 with the HD 1.4 converter on the camera or the FA 77. So that is why I am a bit surprised and wondering if it is the new lens (DFA 24-70) or the new camera. But you are right, I need to test the AF with my trusted lenses as well, but for that I will print calibration charts and take time to do it right this weekend.

What I have done so far is camera on a tripod, with a remote trigger to fire with a 2 sec delay. Is it necessary to do the calibration under artificial light? Or is normal daylight sufficient?

09-19-2016, 09:15 AM   #5
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My FA31 and FA77 needed some tweaks. I can't figure out how to do the 24mm at a useful distance with the chart so that's uncalibrated. It seems my FA50 needs a bit of adjustment as well, as it seems to miss here and there, particularly at f/2.8. I guess at f/4 it's close enough that it's still sharp.

I rented a FA31 because mine was in need of repairs and that one seemed to focus dead on.
09-19-2016, 09:18 AM   #6
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A reminder. Lenses have tolerance. Mounts on the body have tolerance. The higher the resolution of the sensor the more critical this becomes. The same lens on another body may be a -10 (unlikely) but possible. The tolerances are very very tight for sharp pictures.

My own fine tuning (K-50 and K-3) have been done in daylight. Artificial light attempts were not bright enough in my house.
09-19-2016, 10:26 AM   #7
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QuoteOriginally posted by Lampo Quote
did you have to adjust your autofocus like this?
+10 for my DFA 24-70
09-19-2016, 10:38 AM   #8
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Thanks a lot for all your experiences and thoughts! It seems very logical that tolerances can balance each other out or reinforce each other and that this effect is more pronounced when the depth of field is smaller. I hope it is just the lens, I do not want to part with the K-1 to get it calibrated, we have no distributor in the Netherlands if I recall correctly, so calibrating the camera at Pentax would take probably quite some time...

The K-1 is a very nice piece of equipment, I just love the colours it produces and the white balance and metering has improved vastly over the K-5 IIs. If I can assure that the autofocus works as supposed to, I am absolutely confident that I have found my photographic dream machine for the next years!

---------- Post added 19-09-16 at 19:39 ----------

QuoteOriginally posted by Nuij Quote
+10 for my DFA 24-70
Ah, so you had a big adjustment on your DFA 24-70 as well? What about your other lenses?

09-19-2016, 11:49 AM   #9
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I've had to fine tune all of lenses except the FA 31mm Ltd. Some lenses were in the negative and some were in the positive.
09-19-2016, 12:14 PM   #10
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QuoteOriginally posted by Lampo Quote
Ah, so you had a big adjustment on your DFA 24-70 as well? What about your other lenses?

Not tested yet.
09-19-2016, 12:45 PM   #11
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QuoteOriginally posted by Lampo Quote
Somehow it does not feel right to have such a major adjustment on a new lens and camera.
It's perfectly normal. We're lucky that Pentax offers a way to do this in-camera. Some brands don't. Sigma goes the other way, and sell a docking station specifically to adjust AF on their lenses.

QuoteOriginally posted by jatrax Quote
Now if ALL lenses were off +10 then I might consider sending the camera in for calibration. But not without extensive testing on a number of lenses.
Even then, just offset the camera to +10 and call it a day.

QuoteOriginally posted by jatrax Quote
Just the movement caused by your finger on the shutter button can skew the test.
It's best to use a remote, or the phone app.

QuoteOriginally posted by UncleVanya Quote
. The higher the resolution of the sensor the more critical this becomes.
True, but for reference, it's mostly the pixel pitch which is important. for instance, the K-3 will show more "problems" than the K-1, because its pixels are smaller. The CoC will be smaller also.
09-19-2016, 01:25 PM   #12
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QuoteOriginally posted by Nuij Quote
+10 for my DFA 24-70
Exactly the same with mine....
09-19-2016, 01:55 PM   #13
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I've fine adjusted every single lens.
09-19-2016, 03:14 PM   #14
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DFA 24-70 and 15-30 +10 =(
09-19-2016, 07:30 PM   #15
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My Sigma 24-60 was -8 on the K3 and the Sigma 70-200 OS HSM & Pentax-F 300 were spot on. With the K-1 the 24-60 is spot on at all lengths and the two teles required an adjustment of +4 & +2 respectively. If you are getting the tolerance fit with the in camera adjustment you should be alright.
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