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6 Days Ago   #1
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On multiple bodies do lenses need consistent focus adjustments?

Does anyone have one lens needing a -5 and +3 for one lens. Yet the opposite for another? Say +3 and -5 for another? Or perhaps several lenses needing the same correction on one body but all different on another body?
What would cause this? Perhaps very slight decentering and other lens and mount variations?
Post your data or thoughts.

6 Days Ago   #2
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The short answer is no. The fine adjustment value is based on the interaction between the PDAF sensor and the lens' optical characteristics during focus. An adjustment determined on one body might be spot on another body, but might not.


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6 Days Ago   #3
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QuoteOriginally posted by swanlefitte Quote
Does anyone have one lens needing a -5 and +3 for one lens. Yet the opposite for another? Say +3 and -5 for another? Or perhaps several lenses needing the same correction on one body but all different on another body?
What would cause this? Perhaps very slight decentering and other lens and mount variations?
Post your data or thoughts.
No, the adjustments needed may vary.

Adam
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6 Days Ago   #4
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QuoteOriginally posted by stevebrot Quote
The short answer is no. The fine adjustment value is based on the interaction between the PDAF sensor and the lens' optical characteristics during focus. An adjustment determined on one body might be spot on another body, but might not.


Steve
No? Not sure to what. All yours lenses with +1 adjustments on one body all have -7 on another body? If I have 20 lenses and 8 are all +1 on one body I would think if I adjusted one on another body that adjustment would be almost the exact same for all 8 lenses on the other body instead of all over the board.

6 Days Ago - 1 Like   #5
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My personal experience - using a K-3II, K-3 and K-5 - is that the additive or subtractive offset is consistent between bodies once you've established a baseline for each. So... let's say Body A requires zero adjustment with Lens #1 and Body B requires +3 adjustment with the same lens. If Body A requires -5 adjustment with Lens #2, Body B will need a -2 adjustment for that lens. If Body A requires a +6 adjustment with Lens #3, Body B will need +9 adjustment.

It's also proven consistent with my K10D and GX-10 bodies, although the AF fine adjustment steps and the direction of adjustment differ. A +1 adjustment on the K-3II / K-3 / K-5 translates to a -20 adjustment in DEBUG on the K10D, while a -1 adjustment translates to +20. But otherwise, the behaviour is consistent.

In fact, I have a spreadsheet that I use to record and manage the AF fine adjustment settings for all of my lenses on all of my bodies. I use my K-3 as the reference, since (very fortunately) it requires zero adjustment with most of my DA Limited lenses and is within +/-5 for every other AF lens I own. Having calibrated all of my lenses on the K-3, I only need to calibrate one lens on each of my other bodies to get a baseline value, then I calculate the required adjustment for each body / lens combo. It works a treat

Last edited by BigMackCam; 6 Days Ago at 02:09 PM.
6 Days Ago   #6
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QuoteOriginally posted by Adam Quote
No, the adjustments needed may vary.
That seems to imply lens variation could mean we have the same lens and same body and neither like the performance but if we swap lenses we may both see improvement.
6 Days Ago   #7
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QuoteOriginally posted by BigMackCam Quote
My personal experience - using a K-3II, K-3 and K-5 - is that the additive or subtractive offset is consistent between bodies once you've established a baseline for each.
I would expect this but it's not clear this is normal behavior. I hope more ppl will chime in on what happens for them.
6 Days Ago   #8
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QuoteOriginally posted by swanlefitte Quote
I would expect this but it's not clear this is normal behavior. I hope more ppl will chime in on what happens for them.
It's definitely worth waiting for others' input.

I will say, though, the behaviour I've mentioned is demonstrable across all of my bodies - K-3II, K-3, K-5, K10D, 3 x GX-10, GX-1L and *ist DL. The only gotcha is on those last two, where close range focusing with certain lenses seems to require different AF fine adjustment settings for absolute accuracy. I put that down to the older AF algorithms. But the rest of the bodies mentioned have proven consistent...

6 Days Ago - 1 Like   #9
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QuoteOriginally posted by BigMackCam Quote
My personal experience - using a K-3II, K-3 and K-5 - is that the additive or subtractive offset is consistent between bodies once you've established a baseline for each. So... let's say Body A requires zero adjustment with Lens #1 and Body B requires +3 adjustment with the same lens. If Body A requires -5 adjustment with Lens #2, Body B will need a -2 adjustment for that lens. If Body A requires a +6 adjustment with Lens #3, Body B will need +9 adjustment.

It's also proven consistent with my K10D and GX-10 bodies, although the AF fine adjustment steps and the direction of adjustment differ. A +1 adjustment on the K-3II / K-3 / K-5 translates to a -20 adjustment in DEBUG on the K10D, while a -1 adjustment translates to +20. But otherwise, the behaviour is consistent.

In fact, I have a spreadsheet that I use to record and manage the AF fine adjustment settings for all of my lenses on all of my bodies. I use my K-3 as the reference, since (very fortunately) it requires zero adjustment with most of my DA Limited lenses and is within +/-5 for every other AF lens I own. Having calibrated all of my lenses on the K-3, I only need to calibrate one lens on each of my other bodies to get a baseline value, then I calculate the required adjustment for each body / lens combo. It works a treat
Nice system, I think I need to drag out the spreadsheet and copy your method
6 Days Ago   #10
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I think the calculation is good as a starting point. I would fine-tune it anyway. Because when I try to adjust the auto focus, I want to make it as accurate as possible.
6 Days Ago   #11
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I would check if one body needs a global adjustment too. If it's impossible to calibrate all lens with about the same value plus a global adjustment on all bodies that sounds weird, but possible. The lenses has many calibration values in their chips...
6 Days Ago   #12
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QuoteOriginally posted by swanlefitte Quote
What would cause this?
Production tolerances for the cameras and lenses are the reason for that.
If you match a lens that is on the longer end of the tolerances (distance mount to optical elements wise) and a camera on the lower end (flange focal distance below the optimum of 45.46 mm for Pentax K) then you might need no focus adjustment. Same goes for a shorter lens and a longer camerabody combination and a perfect lens length and perfect camerabody lengt combination will also need little to no adjustment.
Matching a longer lens with a longer camerabody (or short lens, short body) on the other hand will use the entire focus adjustment boundaries of the camera.
Knowing all focus adjustment settings for all your lenses on one camera should theoretically allow you to transfer them onto another camerabody after matching one lens to the new camera, as long as the step width of the focus adjustment for each camera stays the same (otherwise you will need to match at least a second lens to extrapolate your needed values)
6 Days Ago   #13
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The adjustments certainly have varied between cameras I have had (k-x, K-5, K-1).

Although it will vary between sets of camera gear, for me it seems like the adjustment is compensating for something like 75% for tolerances in the camera and 25% in the lens itself. For example on my K-1 my lenses end up with a similar setting (+5 +/- 2) but quite different on say the K-5 (+9 +1/-2).
6 Days Ago   #14
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Despite the way we talk about it, you're not actually calibrating the lens, you're matching the software in the camera to the lens, calibrating the camera as it were. The variation comes from the differences among the camera bodies, not the lenses.
6 Days Ago - 1 Like   #15
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QuoteOriginally posted by dlh Quote
Despite the way we talk about it, you're not actually calibrating the lens, you're matching the software in the camera to the lens, calibrating the camera as it were. The variation comes from the differences among the camera bodies, not the lenses.
That's mostly true... However, there is usually some variation between copies of the same lens due to tolerances in manufacturing and assembly. So AF fine tuning is adjusting the camera in software for individual variances in both the camera body and lens...
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