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04-12-2016, 07:56 AM   #1
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Consistency of autofocus fine adjustments

A hypothetical question (so far, anyway): Is this kind of scenario possible, or would it be indicative of, for example, user error or extreme sloppiness in a lens mechanism:

Camera #1, lenses #1 through #6 all need some degree of moderate positive AF adjustment, like +3 or +5 (doing standardized tests--tripod, same flat high contrast target, single focus point, etc.). Camera #2, lenses #1 through #5 all need a similar degree of modest positive AF adjustment, like +3 or +5, but lens #6, on camera #2, needs a negative adjustment (for example, -4).

Put differently: if most lenses (#1 through #5) behave similarly across both cameras (thus suggesting that there's little camera-to-camera variance), is it possible that one lens could still behave in radically different ways across cameras? If the camera bodies don't vary much, if at all, could a particular lens still mesh in very different ways with each body? Thanks for any insight.

04-12-2016, 08:16 AM   #2
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I found it odd when I calibrated my lenses on two k3 bodies. Like you, mostly, all had between +2 and +7 and they were identical for both bodies. So there was negligible camera to camera variation. I'd been led to understand that this is unusual. Perhaps it isn't.

Can't understand why the variance of one lens. The was it zoom or prime ?
04-12-2016, 09:06 AM   #3
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Without knowing your exact testing procedure it is hard to say but when I see an outlier like that the first suspect would be the testing process. Certainly anything is possible and if the lens is a zoom perhaps even more possible. But if it were me I would re-do the tests on that lens to double check. Maybe you already did that?

Another thought is that there might be some slop in the lens mount. Some third party lenses have been known to develop loose mount screws introducing just a minor bit of looseness in the mount. You don't say which lens but this is something to check. You might also run the test on both cameras again taking the lens off and remounting during the test to see if that has any impact.
04-12-2016, 01:36 PM   #4
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Last year I calibrated the (recently repaired) 100-300 F4 Sigma, 150-500 Sigma HSM (repaired last year) and 18-135 on K-5, K-30 & K-3 - and the conclusion was that the K-3 needed repair/recal. So, which ever body/lens was the odd man out probably wanted fixing (the K-3 went to the Pentax repair centre, so. hopefully it is now "OK").


Last edited by jeallen01; 04-12-2016 at 01:53 PM.
04-12-2016, 07:00 PM   #5
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I did fine tune adjustment with my k30 about 6 months ago. All my Pentax lenses did just fine. I have 2 Sigma lenses 18-200 and 70-300. I adjusted the 18-200 first and then the 70-300. I do not remember the exact number of the adjustments for both lenses, I do know they were not the same. Once I did the adjustment on the 70-300 the camera did not save the adjustment for the 18-200. I went through this process again thinking that I made a mistake. But what ever the adjustment was set to for the last Sigma lens I set was used no matter which lens I had on the camera. As I said, all the Pentax lens adjustments were saved and the adjustment was applied as I changed lenses. I was just wondering if anyone has had the same experience?
04-12-2016, 09:07 PM   #6
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QuoteOriginally posted by macman24054 Quote
I was just wondering if anyone has had the same experience?
The camera saves the settings in a memory slot using the lens ID code presented by the lens. Pentax lenses all use a unique ID code. Unfortunately some third party lenses re-use the same lens ID code so to the camera they appear to be the same lens.
If you have Lightroom or an EXIF reader check a file made using each lens and you will likely find the same ID code for both lenses.
04-13-2016, 04:24 PM   #7
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QuoteOriginally posted by jatrax Quote
The camera saves the settings in a memory slot using the lens ID code presented by the lens. Pentax lenses all use a unique ID code. Unfortunately some third party lenses re-use the same lens ID code so to the camera they appear to be the same lens.
If you have Lightroom or an EXIF reader check a file made using each lens and you will likely find the same ID code for both lenses.
Thanks for the info
04-16-2016, 08:43 AM   #8
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Yes, thanks to all who responded to my question.

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