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06-21-2015, 09:19 AM   #1
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Using K-5 focus corrections on K-3?

I just bought a new K-3, and I realized that I have a boat load of focus adjustments I did on all my lenses (well, really 3 of them needed it) on my K-5. Previous I found a simple way of doing focus adjustments, in camera without specialized and expensive charts, but apparently the tides of the internet has washed this method away (which is a shame, it worked beautifully). If I just stick each of my lenses on the K-5, copy the lens adjustment number, and then enter that into the K-3, would that work?

I somewhat doubt that this will work. If not, does anyone know that method I'm talking about? I know it involved getting a high contrast target and a tripod; and then somehow coming up with a series of focus correction values, and picking the middle on. Or something like that. It was crude, but had great results on both my 77ltd and 40ltd (a huge improvement on the former, actually).

If I remember right, it involved getting critical focus on a target at some [focal length]x[distance] in live view, then switching to normal focusing, autofocusing, and if there was a noise you... did something. And then you got a range of numbers, somehow, and then picked towards the middle, when there was no adjustments in focus between live view, and autofocus... Something like that, but I can't find the details ANYWHERE. It seems that Canikon has an automated feature that does this, and this feature ate Google, since it is all I can find now (especially since Google ignores sensible booleans now).


Last edited by Omestes; 06-21-2015 at 09:24 AM. Reason: some memories, and a gripe.
06-21-2015, 09:28 AM   #2
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Each camera is different. The AF system in the K3 is entirely new. You may find your lenses focus correctly on the K3 when they did not on the K5. In short, you have to redo the entire process for each lens.
06-21-2015, 09:32 AM   #3
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Every camera is different. Your lenses would not be the same on another k-5 either. You have to test and adjust them on every camera you use.
06-21-2015, 09:36 AM   #4
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QuoteOriginally posted by MadMathMind Quote
Each camera is different. The AF system in the K3 is entirely new. You may find your lenses focus correctly on the K3 when they did not on the K5. In short, you have to redo the entire process for each lens.
The problem is that I can't remember how I did it. I just know, you got correct focus with live view (using contrast detect), and then switched to normal focusing, and half pressed the shutter to get a beep, if there was any adjustment you... did something. And somehow ended up getting a range of -/+ values, of which you picked the average or middle of the range and the correction factor.

I figured that I couldn't just copy the values, that would make life too easy.

After over 40 minutes of Google-fu, I found two articles on the method I was talking about, one from RiceHigh, and one called "Dot Tune", I think, but am not completely sure it was the "Dot Tune" one I used to pretty decent results.


Last edited by Omestes; 06-21-2015 at 09:52 AM. Reason: found it!
06-21-2015, 10:29 AM   #5
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Did you try them already without any adjustments? Maybe you are lucky and your new camera does not need any...

But otherwise probably your old settings are a good start - if you had to adjust only some lenses on the old body - chance is it has more to do with lenses being a little off and not so much the the camarea af sensor alignment. If K-3 can handle AF better - probably you only need to move your adjustment 1 or 2 steps towards the zero

Last edited by npc; 06-21-2015 at 10:35 AM.
06-21-2015, 10:38 AM - 1 Like   #6
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^^^ This. On my k-5 all lenses required an adjustment. On the k-5IIs a couple did, on the k-3 only one showed an error and it was less then +1 so I left it alone.

There are a number of different methods. I use the Spyder Lenscal system now. But I have tried Dot tune and found it worked although I thought it was a lot more fussy than the lenscal.

Another method is using moire patterns on a screen: Using Moire' Interference Patterns to Test DSLR Auto Focus

Here is a simple paper chart that will work: https://www.pentaxforums.com/forums/6-pentax-dslr-discussion/33853-charts-aut...ed-pentax.html

Whichever you use the most important part is taking your time and being precise. Often the margin of error in these tests, if not done precisely, is larger than the original error. This just leaves you with a randomly adjusted lens.

Last edited by jatrax; 06-21-2015 at 04:23 PM.
06-21-2015, 10:54 AM - 2 Likes   #7
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QuoteOriginally posted by MadMathMind Quote
Each camera is different.
QuoteOriginally posted by jatrax Quote
Every camera is different.
What they said.

With your K-3 the task is easier since you can confirm with focus peaking in magnified live view. The trick is to separate random error from focus bias. I generally recommend that users do a simple evaluation before concluding that a focus adjustment is needed.* Using a flat** target at 20x the focal length distance and with the aperture set to maximum*** :
  • AF turned off
  • Manually de-focus the lens to the minimum focus distance
  • AF turned on
  • Acquire focus using the PDAF (non-live view) system
  • Turn AF off
  • Switch to Live View (focus peaking turned on)
  • Press the OK button to magnify to 100%
  • Evaluate whether the image is in focus and whether you adjust closer or farther to correct
  • Record "0" for no change, "-1" for closer, or "+1" for farther
  • Do the above steps five times
Repeat the above except with the lens de-focused to infinity. What the above flow does is provide a simple three-state statistical sampling of the AV results. A preponderance (4 or more) for any of the three possible results for the total of 1o focus attempts indicates whether there is a need to attempt calibration and whether you need to add or subtract. If you need stronger proof, add 10 more attempts for a total of 20. Note that for lenses having moving elements (zooms and/or internal focus), the results are specific to the focal length and/or target distance.

Should you determine that front/back focus exists, I would suggest making corrections in single increments. Checking the results using the above flow between increments. I know, it is tedious, but at least there will be a minimum of rework.


Steve

* My conclusion after reading literally hundreds of AF adjustment threads is that many (most?) users are chasing shadows and making things worse rather than better. As Jatrax so nicely put it,
QuoteOriginally posted by jatrax Quote
Often the margin of error in these tests, if not done precisely, is larger than the original error. This just leaves with a randomly adjusted lens.
As for myself, I have a single lens correction stored for my K-3 for my Sigma 17-70 (C), one which I intend to get rid of once I calibrate that lens using the Sigma dock.

** While the various 45-degree angle charts are quite popular and also very useful, it is difficult to use them to assess precision at a level smaller than the smallest increment on the chart scale. The fine adjustment on the camera uses smaller increments.

*** There is anecdotal evidence that the K-3 uses a less rigorous AF algorithm when the camera is set to narrower taking apertures.

Last edited by stevebrot; 06-21-2015 at 11:12 AM.
06-21-2015, 11:13 AM   #8
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QuoteOriginally posted by Omestes Quote
I just bought a new K-3, and I realized that I have a boat load of focus adjustments I did on all my lenses (well, really 3 of them needed it) on my K-5. Previous I found a simple way of doing focus adjustments, in camera without specialized and expensive charts, but apparently the tides of the internet has washed this method away (which is a shame, it worked beautifully). If I just stick each of my lenses on the K-5, copy the lens adjustment number, and then enter that into the K-3, would that work?

I somewhat doubt that this will work. If not, does anyone know that method I'm talking about? I know it involved getting a high contrast target and a tripod; and then somehow coming up with a series of focus correction values, and picking the middle on. Or something like that. It was crude, but had great results on both my 77ltd and 40ltd (a huge improvement on the former, actually).

If I remember right, it involved getting critical focus on a target at some [focal length]x[distance] in live view, then switching to normal focusing, autofocusing, and if there was a noise you... did something. And then you got a range of numbers, somehow, and then picked towards the middle, when there was no adjustments in focus between live view, and autofocus... Something like that, but I can't find the details ANYWHERE. It seems that Canikon has an automated feature that does this, and this feature ate Google, since it is all I can find now (especially since Google ignores sensible booleans now).
Wishful thinking... each camera is manufactured with certain amount of tolerance to the specification. Can't even do that on two k-5 or k-3....

06-21-2015, 02:49 PM   #9
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We also have a guide here:
Fixing Front and Back Focus - Introduction - In-Depth Articles

I would start by seeing if you are getting unsharp photos in real life. If so, go ahead and perform calibrations. You may or may not need to, depending on your luck

Adam
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06-21-2015, 03:45 PM   #10
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QuoteOriginally posted by stevebrot Quote
* My conclusion after reading literally hundreds of AF adjustment threads is that many (most?) users are chasing shadows and making things worse rather than better. As Jatrax so nicely put it,
It really only made a noticable difference on two lenses (the 77 and the 40), the others it was probably more psychological.

QuoteOriginally posted by Adam Quote
I would start by seeing if you are getting unsharp photos in real life. If so, go ahead and perform calibrations. You may or may not need to, depending on your luck
I haven't noticed anything yet, but I wanted the information at hand just in case, I remember being very disappointed with my 77ltd because it was consistently soft wide open, tweaking it a fair amount (something like -7) made a huge difference. I really need to go out and shoot with all my lenses on the new body, but it is so hot right now that it is hard to get the motivation. I keep meaning to take an outing with a single body, and a single lens once a week or so, and having a new K-3 is about the best excuse (for diagnostics, not fun, of course )
06-21-2015, 04:45 PM   #11
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I found that some lenses that required adjustments with my k-5 could be used without adjustments with my k-3.
06-22-2015, 03:38 AM   #12
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I generally use live view for an estimate of auto focus adjustment needed and it really seems to work well. This is an article on it: AF microadjustment for the 1Ds mark III, 1D Mk3, 5D Mk2, 7D, 1D X
06-22-2015, 08:29 AM   #13
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I managed to mess around with a couple lenses last night, and it seems like at least a couple of the ones that had adjustments don't need them. On the other hand, it seems it takes more work on the K3 to get sharp shots at longer focal length, thanks to those extra pixels. I'm going to have to work on my hand held macro and tele skills again
06-22-2015, 08:31 AM   #14
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QuoteOriginally posted by stevebrot Quote
What they said.

With your K-3 the task is easier since you can confirm with focus peaking in magnified live view. The trick is to separate random error from focus bias. I generally recommend that users do a simple evaluation before concluding that a focus adjustment is needed.* Using a flat** target at 20x the focal length distance and with the aperture set to maximum*** :
  • AF turned off
  • Manually de-focus the lens to the minimum focus distance
  • AF turned on
  • Acquire focus using the PDAF (non-live view) system
  • Turn AF off
  • Switch to Live View (focus peaking turned on)
  • Press the OK button to magnify to 100%
  • Evaluate whether the image is in focus and whether you adjust closer or farther to correct
  • Record "0" for no change, "-1" for closer, or "+1" for farther
  • Do the above steps five times
Repeat the above except with the lens de-focused to infinity. What the above flow does is provide a simple three-state statistical sampling of the AV results. A preponderance (4 or more) for any of the three possible results for the total of 1o focus attempts indicates whether there is a need to attempt calibration and whether you need to add or subtract. If you need stronger proof, add 10 more attempts for a total of 20. Note that for lenses having moving elements (zooms and/or internal focus), the results are specific to the focal length and/or target distance.

Should you determine that front/back focus exists, I would suggest making corrections in single increments. Checking the results using the above flow between increments. I know, it is tedious, but at least there will be a minimum of rework.


Steve

* My conclusion after reading literally hundreds of AF adjustment threads is that many (most?) users are chasing shadows and making things worse rather than better. As Jatrax so nicely put it,

As for myself, I have a single lens correction stored for my K-3 for my Sigma 17-70 (C), one which I intend to get rid of once I calibrate that lens using the Sigma dock.

** While the various 45-degree angle charts are quite popular and also very useful, it is difficult to use them to assess precision at a level smaller than the smallest increment on the chart scale. The fine adjustment on the camera uses smaller increments.

*** There is anecdotal evidence that the K-3 uses a less rigorous AF algorithm when the camera is set to narrower taking apertures.
All you said + lens image placement within the DoF is never (rarely) 50:50 and where the target should be is defined by lens focal length, Target distance and aperture.

Anyone 'calibrating' their lens without using correct data (many DoF calculators will tell you the split ) have randomized their lens focusing capabilities

Note how there is indeed a subtle change for the smallest focal lengths. This is a real effect, but is negligible compared to both aperture and focusing distance. Even though the total depth of field is virtually constant, the fraction of the depth of field which is in front of and behind the focus distance does change with focal length, as demonstrated below:
Distribution of the Depth of Field
Focal Length (mm) Rear Front
10 70.2 % 29.8 %
20 60.1 % 39.9 %
50 54.0 % 46.0 %
100 52.0 % 48.0 %
200 51.0 % 49.0 %
400 50.5 % 49.5 %

Understanding Depth of Field in Photography
07-06-2015, 07:00 PM   #15
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My quick'n'dirty method is to put two same strips of masking tape on the lens - one on the rotating focus ring and one on the fixed section of the barrel. Use a tripod so distance to subject remains perfectly static. Use an subject at desired test range. Focus with liveview. Check all looks ok with magnified liveview (and focus peaking if you have it). Mark a line across both pieces of tape. This is now the reference point for where the focus is spot-on. Now repeatedly focus using PDAF and observe the alignment of the marks on the tape. Work out whether an back focus or front focus is present (which can simply be gleaned from how the marks misalign). Start dialling in AF correction and retest until get fairly consistent results. Then move to some 10-15 metres distance from an object and retest. It may be necessary to compromise between two AF settings. Some of the hacking threads on the net suggests that lens firmware for the Pentax dslr system holds separate focus calibration data for two distances ('Near' and 'Far') which could provide a logical explanation of why the calibration may vary slightly between close and distant targets. In fact I think this selection between near and far for a given shot can be seen buried in the EXIF data of images.

What I found interesting from having a go with this method last weekend is the variability of individual PDAF attempts with my K-3. With an aligned mark on the lens, small variations in stopping positions upon multiple attempts are obvious and surprisingly frequent. Enough that when switching to magnified liveview, you can see that the acquired focus was not always optimal. The AF stopping point also looked to have some observable biases depending on whether you were starting at infinity or min. distance.

Liveview focus conversely was highly repeatable at where it stopped, but even then, just a touch more accuracy could be sometimes be extracted manually focussing using magnified viewing and focus peaking. Probably corresponding to the slop in the screw drive mechanism as the adjustment between liveview AF and what I judged to be optimal was no more than a 1mm or so of movement in the focus ring.

++++ This method obviously won't work for lenses that do not rotate the focus ring when autofocusing (I've just bought one such lens, so will need to use an alternate method for that lens). ++++

The bottom line take away I got from this exercise is that I should use liveview or even manually focus via focus peaking when I really really want critical focus (eg exposing at maximum apertures where shallow DOF won't hide small focus errors).

As an additional note, I got round to updating my K-3 firmware from v1.0 straight through to V1.21 last night. I hadn't experienced any of the mirror flop issues reported by others so had no pressing imperative to update. What I think I have seen though is some change to the AF correction required by the lens I happened to have on at the time. This might be due to factors not related to the firmware (eg different lighting - daylight vs artificial) but I will now need to evaluate this more carefully. I previously found I had quite a few lenses near the +10 mark, and the lens I was playing with last night suddenly looked to be much closer to nil adjustment. So maybe the firmware updates along the way have updated some of the PDAF algorithms (in a good way).

I will have a play about on the coming weekend in daylight and report back - middle of winter here so no free time at home on weekdays during good daylight hours.

Some of my lenses have appeared to need more than +10 correction so if the firmware updates have indeed improved AF performance, I may be able to avoid fiddling about in the debug menu. The firmware update to V1.21 last night was a precursor to see if this could be avoided. If will also be interesting to see if the variability of individual PDAF attempts is reduced.
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