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09-29-2019, 07:32 AM   #1
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K-1 soft images: AF Fine Adjustment or Body issue?

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Morning all,
I've been struggling lately with a higher percentage of soft photos than I'm used to, and refusing to believe that I'm just that bad of a photographer I dropped the money to get the latest FocusTune/LensAlign package and have started to check my lenses. I've tested 5 different setups now and the results are making me wonder if I need to send my K-1 body in for service. Thoughts and insights appreciated:

D FA 24-70 at 24mm: +1
D FA 24-70 at 70mm: +10

D FA* 50mm: +6
D FA WR 100mm: +6

D FA* 70-200 at 70mm: ~+12 (AF Fine Adjustment maxes out at +10)
D FA* 70-200 at 200mm: +10

FA* 200mm: +10


What I'm noticing is that the results for each lens say they are back focused by a decent amount which makes me wonder if there's something out of alignment in my body. I feel fairly comfortable in my testing setup (but I'm still open to it being human error) having watched the setup and alignment video a half dozen times now to make sure I understood it, and I've realigned the camera and test device for each of the above setups. Have others seen this much adjustment needed on their lenses?

Edit: Autofocus is set to use a single focus point and between 6-10 images were taken at each AF adjustment so the software can get some good averages.
Edit2: Added adjustment values for the 70-200 at 200mm as well as for the FA* 200 prime. That's all of the autofocus lenses that I have.


Last edited by CoreyC; 09-29-2019 at 12:35 PM.
09-29-2019, 07:59 AM   #2
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Does the adjustment then give you perfect shots?

My K1 needs approx +6 to +10 on all my lenses
09-29-2019, 08:06 AM   #3
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QuoteOriginally posted by CoreyC Quote
D FA 24-70 at 24mm: +10. D FA* 70-200 at 70mm: ~+12 (AF Fine Adjustment maxes out at +10)
You'd start by fine tuning AF for the middle of the zoom ranges (50mm and 135mm), or even with zooms fully extended (70mm and 200mm).
09-29-2019, 08:09 AM   #4
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QuoteOriginally posted by pschlute Quote
Does the adjustment then give you perfect shots?

My K1 needs approx +6 to +10 on all my lenses
I haven't taken them out in to the real world yet, there's a group shoot later today I'll be attending specifically to test if the adjustments improve things.

It is good to know, albeit a bit disheartening, that I'm not the only one that is seeing this amount of adjustment needed for all of their lenses.

09-29-2019, 08:15 AM - 1 Like   #5
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In real world shooting (f4, f5.6, f8) of medium distant subjects, lack of sharpness is not related to AF fine adjustment. Shutter speed too low , SR disabled, often steals more sharpness than AF accuracy.
09-29-2019, 09:17 AM   #6
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QuoteOriginally posted by CoreyC Quote
It is good to know, albeit a bit disheartening, that I'm not the only one that is seeing this amount of adjustment needed for all of their lenses.
I think you are approaching this from the wrong angle.

In years gone by when we used film, any inaccuracy in AF was hidden by the fact we generally looked at small prints or DOF hid the effect.

Same was true to a degree with the first DSLRs. But now with big MP sensors we are able to peek at our images like never before. And we have discovered what the camera manufacturers already knew. Manufacturing tolerances added to the behaviour of different lenses means that perfect AF alignment will not be achieved out of the box. This is why Pentax and all other DSLR makers have a AF/FA menu. So you can tune your camera to each individual lens. In the unlikely event that your camera/ lens combos need an adjustment more than the +10/-10 allowed, then Pentax will adjust to zero free of charge. Just make sure you send them a lens and camera to re-calibrate.
09-29-2019, 09:52 AM - 1 Like   #7
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QuoteOriginally posted by pschlute Quote
I think you are approaching this from the wrong angle.

In years gone by when we used film, any inaccuracy in AF was hidden by the fact we generally looked at small prints or DOF hid the effect.

Same was true to a degree with the first DSLRs. But now with big MP sensors we are able to peek at our images like never before. And we have discovered what the camera manufacturers already knew. Manufacturing tolerances added to the behaviour of different lenses means that perfect AF alignment will not be achieved out of the box. This is why Pentax and all other DSLR makers have a AF/FA menu. So you can tune your camera to each individual lens. In the unlikely event that your camera/ lens combos need an adjustment more than the +10/-10 allowed, then Pentax will adjust to zero free of charge. Just make sure you send them a lens and camera to re-calibrate.
I get what you're saying Peter. It may be unrealistic, but I do kind of expect that for the prices we're paying for the bodies and lenses that the tolerances should be a bit tighter and that an AF adjustment beyond +/-5 should be the exception. But that's me with my high expectations.

I am going to look into shipping the body and a lens off for service. It's good to hear that they'll adjust to zero free of charge and I'm hopeful that recalibrating one camera/lens combo will have a positive impact on the rest since all my lenses are exhibiting back focusing right now.

09-29-2019, 10:25 AM   #8
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QuoteOriginally posted by CoreyC Quote
get what you're saying Peter. It may be unrealistic, but I do kind of expect that for the prices we're paying for the bodies and lenses that the tolerances should be a bit tighter and that an AF adjustment beyond +/-5 should be the exception.
The trouble with that expectation is this. Yes it can be done. But that means that every body off the production line has to be bench tested with say 5 different versions of 5 different lenses (25 lenses) that have previously been found to require near zero AF/FA adjustment on an equally large test set of bodies. It further means that each lens produced in future needs to be bench tested with say 5 bodies to ensure AF/FA accuracy.

This will no doubt mean less adjustment is required, although any older lens or body that is paired with a newer one could still be wildly out. Costs rise as a result. It is all a matter of degree. I for one am happier to AF/FA all my own lenses individually. I know they are accurate.
09-29-2019, 11:19 AM   #9
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QuoteOriginally posted by CoreyC Quote
It may be unrealistic, but I do kind of expect that for the prices we're paying for the bodies and lenses that the tolerances should be a bit tighter and that an AF adjustment beyond +/-5 should be the exception.
If a fine adjustment is required, it is seldom an issue with the body* and even with the lens is not an issue of manufacturing tolerance in the normal way we might think of such. The usual causes are all optical and would include:
  • Centering defect
  • Longitudinal inconsistencies (element spacing) in focus or zoom groups
  • One of more elements not properly set in place
Any of the above would create ambiguities of focus that may bias out-of-focus detection by the PDAF sensor. Often enough, the issue is worse at some focus distances and zoom settings than at others. Internal focus and zooms tend to be more prone to front/back focus problems.

As noted above, soft results, particularly with a high resolution sensor are more likely due to camera or subject motion, atmospheric conditions, soft lens, and/or allowing shutter release early or late to focus acquisition. Only if a repeatable pattern of clearly demonstrable front focus or back focus is present should a fine adjustment be done. Experience on this site has been that fine adjustment attempts often result in a lot of time wasted and owner frustration with no improvement in field results.

If you are using LensAlign + FocusTune according to directions and the software indicates statistically significant bias across multiple attempts (say 10+ minimum, half from minimum distance stop and half from infinity stop), that is about the best you can attempt without an optical bench. I am curious about your results:
QuoteQuote:
D FA 24-70 at 24mm: +1
D FA 24-70 at 24mm: +10

D FA* 50mm: +6
D FA WR 100mm: +6

D FA* 70-200 at 70mm: ~+12 (AF Fine Adjustment maxes out at +10)
D FA* 70-200 at 70mm: +10

FA* 200mm: +10
What is does the repetition mean for the D FA 24-70 and the D FA* 70-200?


Steve


* It will present as all lenses requiring adjustment in the same direction at all distances and (for zooms) focal lengths. Even if mild, this type of issue is a defect in manufacture of the body and should be covered under warranty.

Last edited by stevebrot; 09-29-2019 at 12:40 PM. Reason: grammar
09-29-2019, 11:23 AM - 1 Like   #10
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A lab can adjust AF to better than factory tolerances by tailoring firmware calibration values to a specific lens. I was offered by Rüdiger Maerz Gmbh (service in Germany) to align my camera with my lens on a bench with MTF targets, to have perfect focus for one lens, but that meant worse accuracy for my other lenses. And by the day I'd buy a new lens that would require -8, it will be impossible to calibrate it if the body was aligned to 0 with lenses that required +8, because I would then need to adjust to -16 for that new lens, which is not possible. That's why the AF fine tuning values in camera are there, based on factory specifications.

Last edited by biz-engineer; 09-29-2019 at 11:31 AM.
09-29-2019, 11:40 AM - 2 Likes   #11
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The first thing to do would be to evaluate the camera using live view. If this consistently delivers sharp results, then the next step would be to look at AF adjustments. If not, then it could be some other issue.


If it turns out to be the AF then, given the need for what appears to be pretty consistent AF adjustments, you may want to send the camera in for calibration.

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09-29-2019, 12:03 PM - 1 Like   #12
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Note about AF calibration targets such as lensalign: Personally I don't use oblique targets for AF fine adjustment because the depth of field in front and back don't have the same depth (1/3rd in front and 2/3rd at the back of the focus plane). While expecting 50% of front DoF and 50% of back DoF by looking at an oblique scale, the well calibrated lens look like it is back focused while it's not. So if AF is adjusted to see best focus in the middle of the oblique scale, an error is introduced by the AF fine tune value (because DoF front/back isn't actually 50%/50% like it seems it should be when looking at the oblique scale). For this reason, I use a newspaper flat on a wall, and I take a set of pictures for each AF fine adjust value from -10 to +10, with the lens pre-focused at infinity and pre-focused nearest distance (because there could be some offset depending on where the lens AF is coming from). Then I successively rank all images from the sharpest to the least (it is easy to do so by side-by-side comparison), once the ranking is done it is easy to read the AF fine tune value that give the average best sharpness.

Last edited by biz-engineer; 09-29-2019 at 12:10 PM.
09-29-2019, 12:33 PM   #13
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QuoteOriginally posted by biz-engineer Quote
the depth of field in front and back don't have the same depth (1/3rd in front and 2/3rd at the back of the focus plane). While expecting 50% of front DoF and 50% of back DoF by looking at an oblique scale, the well calibrated lens look like it is back focused while it's not
At the distances people use to generally AF/FA that is not correct. DOF is more 50/50 at close distance
09-29-2019, 12:39 PM   #14
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QuoteOriginally posted by biz-engineer Quote
Note about AF calibration targets such as lensalign: Personally I don't use oblique targets for AF fine adjustment
LensAlign uses a flat target and an alignment device to assure the target is centered and orthogonal to the lens axis. When coupled with the FocusTune software, a quasi-statistical evaluation is possible for both detection of front/back focus and for confirmation of proper adjustment. The main challenge is to follow directions and understand the process enough to work with the system. Bob Atkins has a decent review:

LensAlign and FocusTune Review - Bob Atkins Photography


Steve

Last edited by stevebrot; 09-29-2019 at 01:02 PM.
09-29-2019, 12:42 PM   #15
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QuoteOriginally posted by stevebrot Quote

If you are using LensAlight + FocusTune according to directions and the software indicates statistically significant bias across multiple attempts (say 10+ minimum, half from minimum distance stop and half from infinity stop), that is about the best you can attempt without an optical bench. I am curious about your results:

What is does the repetition mean for the D FA 24-70 and the D FA* 70-200?


Steve


* It will present as all lenses requiring adjustment in the same direction at all distances and (for zooms) focal lengths. Even if mild, this type of issue is a defect in manufacture of the body and should be covered under warranty.
Steve, the repetition means I was not paying attention with my copy/paste I tested the zooms at both ends of their focal range and the second listing is the longer of the two. I've updated the original post - thanks for pointing that out
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