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04-27-2019, 12:42 PM   #1
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AF Fine Adjustment question

Hello,
My DA 200 mm is not as sharp as I expected, so I'm doing a AF Fine Tune adjustment. On page 63 of the KP Manual, I assume that I need to move the focus back, or to a farther position. Is this correct? Thank you.


Last edited by TerryL; 10-18-2019 at 06:29 PM.
04-27-2019, 01:21 PM   #2
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From your image, yes. But that is not far off.

Apologizes if you already know this but AF fine tuning is a precision process. Quite often the margin of error in the testing procedure is larger than the actual lens error. Making things a bit of a guess. The test should be done on a tripod, with everything perfectly in plane and aligned. And the test should be repeated at least 5 times before you make any changes.

It is quite easy to make things worse as you chase adjustments unless your testing process is spot on. From your image, assuming that is consistent over a number of tests, I would move it back one and then retry to see if it makes any difference.
04-27-2019, 01:30 PM   #3
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Assuming the point of focus was on the barcode and that the camera and chart were properly positioned, there looks to be a very slight front focus and a small adjustment to a farther position might be useful.


Steve

* I have not used this tuning device, but I suspect that the camera was not properly lined up. The camera sensor should be parallel to the barcode target with the intended point of focus at about the same level as the fold/zero line on the chart. Distance to the target will vary according to focal length and the chart-makers recommendations. Evaluate as close to the intended point of focus as possible.

Last edited by stevebrot; 04-27-2019 at 01:38 PM.
04-27-2019, 01:30 PM   #4
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Terry. As has been pointed out before. If you cannot get the test chart aligned with the camera, and do a scientific test like "best out of 10 attempts", you will not get this right.

04-27-2019, 01:40 PM   #5
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QuoteOriginally posted by stevebrot Quote
Assuming the point of focus was on the barcode and that the camera and chart were properly positioned, there looks to be a very slight front focus and a small adjustment to a farther position might be useful.


Steve

* I have not used this tuning device, but I suspect that the camera was not properly lined up. The camera sensor should be parallel to the barcode target with the intended point of focus at about the same level as the fold/zero line on the chart. Distance to the target will vary according to focal length and the chart-makers recommendations. Evaluate as close to the intended point of focus as possible.
I read many posts and watched a few YouTube tutorials. I used a tripod, with 2 second delay. I also made sure my lens was on the same plane as the target. I took about 15 shots at different apertures. I feel pretty confident that my post shows the correct result. Thank you.

---------- Post added 04-27-19 at 01:45 PM ----------

QuoteOriginally posted by stevebrot Quote
Assuming the point of focus was on the barcode and that the camera and chart were properly positioned, there looks to be a very slight front focus and a small adjustment to a farther position might be useful.


Steve

* I have not used this tuning device, but I suspect that the camera was not properly lined up. The camera sensor should be parallel to the barcode target with the intended point of focus at about the same level as the fold/zero line on the chart. Distance to the target will vary according to focal length and the chart-makers recommendations. Evaluate as close to the intended point of focus as possible.
Steve, that's exactly what I was thinking. I'll make very small adjustments, and retest it. Perhaps by 1, or 2. Thank you.

---------- Post added 04-27-19 at 01:51 PM ----------

QuoteOriginally posted by pschlute Quote
Terry. As has been pointed out before. If you cannot get the test chart aligned with the camera, and do a scientific test like "best out of 10 attempts", you will not get this right.
Peter, I will keep learning and trying until I do get it right. Thank you.
04-27-2019, 01:55 PM   #6
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QuoteOriginally posted by TerryL Quote
I also made sure my lens was on the same plane as the target.
OK...perspective clues on the image seems to indicate that the sensor was right of the target and not at right angles to the target plane. This is tough to set up, tough enough that some vendors of expensive tools have alignment aides built into the device. As @jatrax noted above, if alignments are not consistently correct and the same between evaluation, adjustment, and recheck, the user will be chasing an impossible target. (Test looks good, but real world results after adjustment suck...that sort of thing.) Each of us who has responded to this thread have assisted numerous other users in the adjustment process and while I might not know that which I speak, the other folk are pretty sharp.

BTW...take your test image wide open.

Acknowledged! Terry posted a little before me, so I did not have the benefit of the last message above.


Steve

(...I use a different method, but still appreciate chasing bad calibrations when setup was at fault...)

Last edited by stevebrot; 04-27-2019 at 02:05 PM.
04-27-2019, 02:14 PM - 2 Likes   #7
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QuoteOriginally posted by TerryL Quote
Peter, I will keep learning and trying until I do get it right. Thank you.
The intent of the repetition is to account for statistical variance between results. PDAF is fairly imprecise; for example a series of say 20 tries for a camera/lens that is not too far off may result in almost half indicating front focus and the rest indicating no change or mild back focus. The required correction might be a minimal change, if any, to correct front focus or maybe not. I usually do twenty tries simply recording whether front or back was the result and leave things as they are if front count = back count.


Steve
04-27-2019, 02:21 PM   #8
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QuoteOriginally posted by stevebrot Quote
while I might not know that which I speak, the other folk are pretty sharp
That's funny Steve, if you don't know then the rest of us are all in trouble.

One thing I don't think was mentioned was the distance to the target. There is some debate about this and I've heard both 25x focal length and 50x focal length put forth as correct. On longer lenses I am limited by the size of the hallway in my house unless I want to go outside. Here is an article that might have some information on this: What is the correct distance between the LensAlign and the camera. ? MTD Support Center

04-27-2019, 02:48 PM   #9
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QuoteOriginally posted by stevebrot Quote
OK...perspective clues on the image seems to indicate that the sensor was right of the target and not at right angles to the target plane. This is tough to set up, tough enough that some vendors of expensive tools have alignment aides built into the device. As @jatrax noted above, if alignments are not consistently correct and the same between evaluation, adjustment, and recheck, the user will be chasing an impossible target. (Test looks good, but real world results after adjustment suck...that sort of thing.) Each of us who has responded to this thread have assisted numerous other users in the adjustment process and while I might not know that which I speak, the other folk are pretty sharp.

BTW...take your test image wide open.

Acknowledged! Terry posted a little before me, so I did not have the benefit of the last message above.


Steve

(...I use a different method, but still appreciate chasing bad calibrations when setup was at fault...)
Steve, I am familiar with everyone who has posted, and you all are extremely smart, and I have a great deal of respect for everyone. Lens alignment is a tough subject for a lot of people, and I agree that it must be done correctly.

---------- Post added 04-27-19 at 02:55 PM ----------

QuoteOriginally posted by stevebrot Quote
OK...perspective clues on the image seems to indicate that the sensor was right of the target and not at right angles to the target plane. This is tough to set up, tough enough that some vendors of expensive tools have alignment aides built into the device. As @jatrax noted above, if alignments are not consistently correct and the same between evaluation, adjustment, and recheck, the user will be chasing an impossible target. (Test looks good, but real world results after adjustment suck...that sort of thing.) Each of us who has responded to this thread have assisted numerous other users in the adjustment process and while I might not know that which I speak, the other folk are pretty sharp.

BTW...take your test image wide open.

Acknowledged! Terry posted a little before me, so I did not have the benefit of the last message above.


Steve

(...I use a different method, but still appreciate chasing bad calibrations when setup was at fault...)
I have shots from 2.8 to 5.6. I think it will take a small adjustment to get better results. I'll make an adjustment of 1, and retest it.
04-27-2019, 02:59 PM   #10
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Don't have anything to contribute, but am very interested in your approach as both my autofocus lenses (43 and 77) need some adjustment. I don't have a target yet, so I tried eyeballing it and,well, it's good that you have a target
04-27-2019, 03:08 PM   #11
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QuoteOriginally posted by jatrax Quote
One thing I don't think was mentioned was the distance to the target. There is some debate about this and I've heard both 25x focal length and 50x focal length put forth as correct.
Surely all you need to do is to ensure that the target distance is in the 'very far' (7) focus zone of the particular lens. On Pentax lenses this zone usually starts a fair bit further than 50x FL.
04-27-2019, 03:43 PM   #12
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I join the chorus. It's absolutely a must to have the test chart and the camera properly alligned and use a wide aperture. You also need to know the optimal distance to use.
When I do this, I usually take 9 pictures minimum and check the distrubution. Then repeat the test.

I had a hell of a headache trying to find the proper adjustment for my Sigma 18-35 F1.8 and the 40 DA Limited... (had to adjust it to +4 on my K5-II)

Then I decided to pay one leg and one arm for the LensAllign kit and FocusTune software. Now it still a lot of work, but at least I don't get crazy.
04-29-2019, 12:28 AM   #13
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QuoteOriginally posted by stevebrot Quote
The intent of the repetition is to account for statistical variance between results. PDAF is fairly imprecise; for example a series of say 20 tries for a camera/lens that is not too far off may result in almost half indicating front focus and the rest indicating no change or mild back focus. The required correction might be a minimal change, if any, to correct front focus or maybe not. I usually do twenty tries simply recording whether front or back was the result and leave things as they are if front count = back count.


Steve
I think that Steve nails the problem, the imprecising of autofocus.. My best results with af fine tune is some coarse fabric on 100 times the focal length, fully open lens, single point ,shutterspeed 2000 and handheld. That simulates the practical situation. and- hand on the heart- we dont use a tripod as often as we had to
05-01-2019, 10:14 AM   #14
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QuoteOriginally posted by niels hansen Quote
I think that Steve nails the problem, the imprecising of autofocus.. My best results with af fine tune is some coarse fabric on 100 times the focal length, fully open lens, single point ,shutterspeed 2000 and handheld. That simulates the practical situation. and- hand on the heart- we dont use a tripod as often as we had to
AF finde adjustment is tricky - you compensate for several effects. Best focus varies with distance, aperture and also AF precision. AF precision has a lot to do with the pattern, color, light condition, ... or pure luck of your AF enginge. The best advice is to use controllable, typical conditions for your calibration. ANd yes a special targets helps to take most variables out of the equation.
My 77 lens is calibrated on at f/1.8 and a distance of 2m - not 100x 77 mm. I don^t care about focus precision at infinity, but for wide open performance in portrait shots. It still does fine at infinity - precise focus often stay the same between 2m and infinity. With my 70-200 I optimized for f/2.8 at 135 mm. The 200 mm at 2.8 still works OK as well as the 70 mm at 2.8. Here I really had to balance my decision.
Make sure you know your application and settings, adjust your lenses, make many repetitive test shots and get to know your AF system. Settings are typically repeatable after months and years. If not your taste has changed or something happened to your camera/lens. The process is worthe the effort!
Still, buying a new camera means always having to recalibrate lenses on it.
05-02-2019, 02:28 AM   #15
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QuoteOriginally posted by zapp Quote
AF finde adjustment is tricky - you compensate for several effects. Best focus varies with distance, aperture and also AF precision. AF precision has a lot to do with the pattern, color, light condition, ... or pure luck of your AF enginge. The best advice is to use controllable, typical conditions for your calibration. ANd yes a special targets helps to take most variables out of the equation.
My 77 lens is calibrated on at f/1.8 and a distance of 2m - not 100x 77 mm. I don^t care about focus precision at infinity, but for wide open performance in portrait shots. It still does fine at infinity - precise focus often stay the same between 2m and infinity. With my 70-200 I optimized for f/2.8 at 135 mm. The 200 mm at 2.8 still works OK as well as the 70 mm at 2.8. Here I really had to balance my decision.
Make sure you know your application and settings, adjust your lenses, make many repetitive test shots and get to know your AF system. Settings are typically repeatable after months and years. If not your taste has changed or something happened to your camera/lens. The process is worthe the effort!
Still, buying a new camera means always having to recalibrate lenses on it.
zapp you have a point in calibrating the single objective for the mostly used distance, since af performance is not overly constant. I still would like to know what the measuring angle is in single point, my guess is that som of my problems in portraiture is related to a broader angle than expected
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