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08-26-2016, 11:05 PM   #1
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Fine Focus Adjustment on K1

Have a problem with front focusing on a Sigma 24-70mm lens. Tried to use the AF Fine Adjustment function but could see no difference. Any suggestions?


Also noticed in the tutorial on the use of 3rd party calibration tools that it is not clear whether the AF Adjustment function alters phase detect AF, contrast detect AF or both. Any thoughts?

08-26-2016, 11:11 PM   #2
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Hi Neil. A few questions for you. What are you using as a target? What settings are you using on your camera and lens? How far away are you from the target? Are you using the 24mm or the 70mm? Tripod or hand held? We need a little more information from you to be able to answer. Cheers.
08-26-2016, 11:20 PM   #3
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Tested in controlled conditions on a tripod using remote shutter release. Tested at 24 and 70mm, F2.8 and F8. Using a proper printed target set at 45 degrees to lens. About 1.5m away.
08-26-2016, 11:26 PM   #4
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Also used phase detect AF, not contrast detect (with LV).

08-26-2016, 11:34 PM   #5
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What I can say is the fine adjustment only affects the phase detect. Contrast detect is only in live view and is using the sensor, so there cannot be any front or back focus in live view with contrast detect. If it is out of focus in live view, it's because it has miss focused.
08-26-2016, 11:42 PM   #6
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Can you post your test shots? You should only use F2.8 as shallower DoF makes your distance scale easier to see.

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08-27-2016, 12:10 AM   #7
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Yvonne's charts work well PENTAX DSLRs: PART-1. Autofocus Adjustment charts for front and back focusing problems. Good for Pentax, Canon and Nikon.
08-27-2016, 06:20 AM   #8
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Yvon.

08-27-2016, 03:48 PM   #9
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Will post test images as soon I can.


Thanks.
08-28-2016, 04:54 AM   #10
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There's also this method.

08-29-2016, 06:31 AM   #11
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QuoteOriginally posted by NeilS Quote
Have a problem with front focusing on a Sigma 24-70mm lens. Tried to use the AF Fine Adjustment function but could see no difference. Any suggestions?
Curious. I have major issues with this lens on my K3 and K5IIs. I sent it back to Sigma under warranty and they reported they calibrated it.

Still didn't work properly. FFAs didn't help much pre or post calibration. I could get it to focus better within certain ranges, and then it would be off in others. Pretty much I gave up on the lens and moved on. Sigma wouldn't have anything else to do with it unless I sent my bodies in with the lens and being in my busy season I could not do that. By the time I could I was out of warranty.

Fast forward to the K-1, and I decided to give the lens another try. It has been spot on with no FFAs and gets a lot of use now.

Seems these lenses have some issues.
08-29-2016, 03:07 PM   #12
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The 24-70 is new to me. Just purchased second-hand for use on the K1. I have just tried the Dot Tune method listed by deepbluish, but couldn't get the lens to misbehave as in my previous test. Most strange.


I guess that I just have to keep testing to determine the situation(s) when it is not focusing properly. Seems a bit random at present.
08-30-2016, 02:00 AM   #13
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QuoteOriginally posted by NeilS Quote
Using a proper printed target set at 45 degrees to lens.
I would not use a tilted target. You may use a nearby tilted surface as an indicator for FF/BF, but the actual AF target should be parallel to the camera's sensor.

You may want to check out these AF adjustment hints.
08-30-2016, 02:02 AM   #14
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QuoteOriginally posted by gryhnd Quote
Seems these lenses have some issues.
Clearly, given your own experience ("It has been spot on with no FFAs and gets a lot of use now."), it is typically the camera-lens combination that is problematic.
08-30-2016, 02:27 AM   #15
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>>What I can say is the fine adjustment only affects the phase detect. Contrast detect is only in live view and is using the sensor, so there cannot be any front or back focus in live view with contrast detect.<<



This should be the case but regrettably is not always so. Due to an incorrect version of the lens ROM I have such a problem with a Sigma 18-125 HSM lens and my K-r.
Therefore I would always first make a test, if the lens is capable to yield good quality pictures at all by LV manual focussing. Then I would try if this is still the case by LV contrast detection AF. At last I would try phase contrast AF and adjust it if necessary.


Good luck!
Stephan
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