[rlmartindale]

Like it says...how do YOU do your AF fine adjustment?

I have experimented extensively with several camera bodies and lots of lenses, both Pentax branded and third party.

The official way to do this is to setup 40 times the focal length of the lens and then shoot a target and see the results. In fact, the Focustune software suggests just that.

How to optimize focusing accuracy with large-aperture lenses / explore | RICOH IMAGING

FocusTune

HOWEVER, my extensive experience with all of this lead me to use an INFINITY target for AF fine tuning....the results are sometimes significantly different than the closer setup and the real world results with the lenses has been excellent across the board, testing with infinity targets and close items.

So, for me, its an INFINITY target that is the key to good AF fine tuning...how about you?

[pschlute]

HOWEVER, my extensive experience with all of this lead me to use an INFINITY target for AF fine tuning....the results are sometimes significantly different than the closer setup and the real world results with the lenses has been excellent across the board

Can you share some test target chart results for this. I am surprised you can determine any difference in AF/FA when focussing at infinity.

[CarlosU]

Some things I learn by trial and error when I tried to adjust AF for my 100-300 f4.

I tried with the recommended 40 times focal length distance, that is 12 meters for this lens at 300mm. At that distance, at the largest aperture of f4 you get a DOF of 25 cm.

Believe me, it is very difficult to determine the exact plane of focus with that DOF.

I tried again with half that distance (6 meters) with a calculated DOF of 6 cm, much more easier to estimate the actual plane of focus and much easier to do the adjustments. I suppose that, focusing at infinity, it should be way more difficult to determine where the actual plane of focus is.

On the other hand, for me 6 meters is a very frequently used distance for this lens in particular, which I often use for birds and other small creatures. I think you should adjust AF at the distance you use the most with the lens tested.

[stevebrot]

So, for me, its an INFINITY target that is the key to good AF fine tuning...how about you?

Glad infinity works for you. Out of curiosity, what distance are you using for infinity? 2000x the focal length? 4000x?

My EXTENSIVE experience strongly indicates use of a distance more in tune with the pitch of the lens focus helicoid.

I use a flat target at 20x the focal length (or further depending on MFD):

• Minimum five attempts each from both MFD and Infinity stops
• Comparison for each attempt is against magnified live view at 1:1 pixel-to-pixel correspondence
• Recorded is whether in focus and, if not, the focus direction required to correct.
• If front-focus count equals back-focus count (in-focus tallies 1/2 count both directions), no correction is made.

If correction is indicated, adjustment is made in single step increments with repeat of the test above between adjustments. Note that the repetitions are due to the lack of precision (scatter) inherent to PDAF.


Steve

(...is it possible to detect back-focus if evaluating at infinity?...)

[StiffLegged]

I use the Dot Tune method and it worked marvels with an old FA 80-320mm lens. Also sorted an 18-55 DA WR.

Dot Tune thread

[wooly11]

Like it says...how do YOU do your AF fine adjustment?

I have experimented extensively with several camera bodies and lots of lenses, both Pentax branded and third party.

The official way to do this is to setup 40 times the focal length of the lens and then shoot a target and see the results. In fact, the Focustune software suggests just that.

How to optimize focusing accuracy with large-aperture lenses / explore | RICOH IMAGING

FocusTune

HOWEVER, my extensive experience with all of this lead me to use an INFINITY target for AF fine tuning....the results are sometimes significantly different than the closer setup and the real world results with the lenses has been excellent across the board, testing with infinity targets and close items.

So, for me, its an INFINITY target that is the key to good AF fine tuning...how about you?

Actually Focus tune says 25 times the focal length which I find about correct. Has anyone had any success actually using Focus Tune with Pentax files? When I tried to use it, it could not find the AFA in the Exif data even though it is there when you open the data up with other software. I contacted the seller and he chose not to reply with an answer. However the ruler out of the lensalign is brilliant for doing the adjustments.

[kh1234567890]

Glad infinity works for you. Out of curiosity, what distance are you using for infinity? 2000x the focal length? 4000x?

I use a convenient church tower about 1.3 km away. So for my longest AF lens (300mm) it is some 4,333x fl and for my shortest AF (10mm) it is 130,000x

Actually, any distance, as long as it is in the 'very far' focus zone as read back from the lens slip contacts, is fine ...

[stevebrot]

Actually, any distance, as long as it is in the 'very far' focus zone as read back from the lens slip contacts, is fine ...

With the lenses on my shelf, that can be pretty close.*


Steve

* About 10m with my FA 77/1.8

[rlmartindale]

Actually Focus tune says 25 times the focal length which I find about correct. Has anyone had any success actually using Focus Tune with Pentax files? When I tried to use it, it could not find the AFA in the Exif data even though it is there when you open the data up with other software. I contacted the seller and he chose not to reply with an answer. However the ruler out of the lensalign is brilliant for doing the adjustments.

I am in contact with Michael Tapes, who designed Focustune and he had me look for specific lines of code in the cam.dat file with my version of the software.

Sure enough, the Pentax KP was not there, but he has not yet advised how to fix it.

Here is the line of code he wanted me to find...

"Please find the file cam.dat in your installation. It is in a path 'Resources - data". See if this line exists in the file:

["pentax kp"] = { ["alias"] = "Pen-KP", ["fptype"] = "Pentax_1", ["afastatus"] = "skip"},

Please advise. Thanks."

[c.a.m]

Like it says...how do YOU do your AF fine adjustment?

As an essential component of my autofocus and manual focus lens-calibration efforts over the years, I developed a quantitative methodology independently of commercial products, which has been progressively refined. The approach employs several key elements:

• Flat, high-quality printed targets
• Rigorous test set-up and execution
• Multiple test runs for each calibration procedure
• Primary analysis using the ImageJ open-source scientific image analysis package (via its Fiji distribution, which bundles many useful plug-in modules)
• Spreadsheet-based data organization, calculations, and plots
• Logbook and notes

The camera's sensor plane and target are separated by a measured distance, typically at D = 30-50 x focal length. Lighting, exposure, and focusing procedure are carefully controlled. I have found that this approach yields unambiguous AF Fine Adjustment settings.

Details of the methodology, and sample calibrations for manual focus lenses, may be found at the following Pentax Forum article: Achieving Better Manual Focus with the Green Hexagon - PentaxForums.com

- Craig

[stevebrot]

Here is the line of code he wanted me to find...

"Please find the file cam.dat in your installation. It is in a path 'Resources - data". See if this line exists in the file:

["pentax kp"] = { ["alias"] = "Pen-KP", ["fptype"] = "Pentax_1", ["afastatus"] = "skip"},

Please advise. Thanks."

You might want to copy that text into the file. (Make sure you rename and keep the original as a fallback.)


Steve

[rlmartindale]

Glad infinity works for you. Out of curiosity, what distance are you using for infinity? 2000x the focal length? 4000x?

My EXTENSIVE experience strongly indicates use of a distance more in tune with the pitch of the lens focus helicoid.

I use a flat target at 20x the focal length (or further depending on MFD):

• Minimum five attempts each from both MFD and Infinity stops
• Comparison for each attempt is against magnified live view at 1:1 pixel-to-pixel correspondence
• Recorded is whether in focus and, if not, the focus direction required to correct.
• If front-focus count equals back-focus count (in-focus tallies 1/2 count both directions), no correction is made.

If correction is indicated, adjustment is made in single step increments with repeat of the test above between adjustments. Note that the repetitions are due to the lack of precision (scatter) inherent to PDAF.


Steve

(...is it possible to detect back-focus if evaluating at infinity?...)

...suggest using RAW images instead of JPEG, opening them in PS or other and reducing any sharpening before making judgements.

---------- Post added 04-06-21 at 09:24 PM ----------

Can you share some test target chart results for this. I am surprised you can determine any difference in AF/FA when focussing at infinity.

I don't have images but will say that using Focustune at 25 times the focal length of an 18-55 gave a reading of -6 in Focustune and +2 using infinity....other lenses are closer...or further off.

[stevebrot]

...suggest using RAW images instead of JPEG, opening them in PS or other and reducing any sharpening before making judgements.

I exclusively shoot DNG, but don't use actual captures for AF adjust. If I want a minimally processed TIFF from DNG I use dcraw. Now how about your process?

I don't have images but will say that using Focustune at 25 times the focal length of an 18-55 gave a reading of -6 in Focustune and +2 using infinity.

That does not surprise me, particularly if the lens in question is internal focus or a zoom. What was the reason for the adjustment? Was the DA 18-55 front-focusing or back-focusing? Also, how does your process work?

In the interest of transparency, there is a long history of "my AF sucks" help requests where either (unrealistic) infinity AF expectations or (failed) infinity fine adjustment attempts are part of the discussion. There are also dozens of "how do you do AF fine adjustment" threads. That said, the question regarding your method is honest because if there is a way to do it that works, I am all ears.


Steve

(...does not do fine adjust unless the lens is showing frank front-focus or back-focus at commonly used distances and focal lengths...)

[zapp]

Like it says...how do YOU do your AF fine adjustment?

I have experimented extensively with several camera bodies and lots of lenses, both Pentax branded and third party.

The official way to do this is to setup 40 times the focal length of the lens and then shoot a target and see the results. In fact, the Focustune software suggests just that.

How to optimize focusing accuracy with large-aperture lenses / explore | RICOH IMAGING

FocusTune

HOWEVER, my extensive experience with all of this lead me to use an INFINITY target for AF fine tuning....the results are sometimes significantly different than the closer setup and the real world results with the lenses has been excellent across the board, testing with infinity targets and close items.

So, for me, its an INFINITY target that is the key to good AF fine tuning...how about you?

There is no official method and we do not know how Pentax uses the adjustments for individual lenses. Perfect infinite focus may not fit well for close range focus. Test the distance, f-stop and zoom settings you need and go from there. My portrait lenses are not optimized for infinity and wide open, my zooms are set for a decent result at all focal lengths wide open. A super tele should be calibrated at long distance.
Target size s also important 40x focal length is not always best.
Sigma allows for different correction in different focus ranges with PK dock.

[rlmartindale]

I exclusively shoot DNG, but don't use actual captures for AF adjust. If I want a minimally processed TIFF from DNG I use dcraw. Now how about your process?




That does not surprise me, particularly if the lens in question is internal focus or a zoom. What was the reason for the adjustment? Was the DA 18-55 front-focusing or back-focusing? Also, how does your process work?

In the interest of transparency, there is a long history of "my AF sucks" help requests where either (unrealistic) infinity AF expectations or (failed) infinity fine adjustment attempts are part of the discussion. There are also dozens of "how do you do AF fine adjustment" threads. That said, the question regarding your method is honest because if there is a way to do it that works, I am all ears.


Steve

(...does not do fine adjust unless the lens is showing frank front-focus or back-focus at commonly used distances and focal lengths...)

No particular reason to check this lens except to see if i was getting different results from infinity target or a closer target....

The camera used was a K-7 that is not really in service so there wasn't much reason to use the lens...i just wanted to see the results.

Once the lens was set at infinity, the images are really sharp and very good at a variety of focus distances. It just works for me.

---------- Post added 04-06-21 at 10:42 PM ----------

There is no official method and we do not know how Pentax uses the adjustments for individual lenses. Perfect infinite focus may not fit well for close range focus. Test the distance, f-stop and zoom settings you need and go from there. My portrait lenses are not optimized for infinity and wide open, my zooms are set for a decent result at all focal lengths wide open. A super tele should be calibrated at long distance.
Target size s also important 40x focal length is not always best.
Sigma allows for different correction in different focus ranges with PK dock.

what is this PK dock you mention with Sigma lenses?