Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-29-2019, 05:31 PM - 1 Like   #16
Site Supporter
Site Supporter
vector's Avatar

Join Date: May 2015
Location: Alberta
Posts: 181
We just discussed this over past few days over in this thread: Grey market lenses and AF calibration - PentaxForums.com

Every camera ships from the factory with a value set for PDAF calibration. For example my K1 came with a -20um (equals -2 in af fine tuning) while my K5 came at -70um. My tamron 28-75 required more than a -10 adjustment on each camera. I went the route of using debug mode to adjust that global calibration to -30um on my K1 and -120um on my K5 which put my 28-75 within the -10 to +10 range of the AF Fine Tuning scale which is additive on top of the global calibration setting available in Debug mode. Having done this I am pretty sure when you send it in, all they are doing is using the same debug access to change that global calibration setting. By doing so every lens you attach to the camera will have its AF point shifted by the number of steps you add or remove in debug mode - this includes the OVF confirmation for your manual focus lenses. They are not going to start mechanically adjusting your camera's internals unless PDAF is so far out of whack that it can't be corrected using this method. In that case they are more likely to replace parts than to try physically altering them.

If your lenses are consistently at +10 or in the high +'s indicating chronic back focus, I would be tempted to try debug mode and shift that global setting. I understand not everyone is up to hacking their camera but with very minor risk (if you are careful) it is also free.

09-29-2019, 09:41 PM   #17
Site Supporter
Site Supporter




Join Date: May 2015
Location: Melbourne
Posts: 694
QuoteOriginally posted by vector Quote
We just discussed this over past few days over in this thread: Grey market lenses and AF calibration - PentaxForums.com

Every camera ships from the factory with a value set for PDAF calibration. For example my K1 came with a -20um (equals -2 in af fine tuning) while my K5 came at -70um. My tamron 28-75 required more than a -10 adjustment on each camera. I went the route of using debug mode to adjust that global calibration to -30um on my K1 and -120um on my K5 which put my 28-75 within the -10 to +10 range of the AF Fine Tuning scale which is additive on top of the global calibration setting available in Debug mode. Having done this I am pretty sure when you send it in, all they are doing is using the same debug access to change that global calibration setting. By doing so every lens you attach to the camera will have its AF point shifted by the number of steps you add or remove in debug mode - this includes the OVF confirmation for your manual focus lenses. They are not going to start mechanically adjusting your camera's internals unless PDAF is so far out of whack that it can't be corrected using this method. In that case they are more likely to replace parts than to try physically altering them.

If your lenses are consistently at +10 or in the high +'s indicating chronic back focus, I would be tempted to try debug mode and shift that global setting. I understand not everyone is up to hacking their camera but with very minor risk (if you are careful) it is also free.
This is interesting.
Here's what I have found from doing AF fine adjust on my K-3II and my K-1.

K-1
DFA 150-450 @450 +10
Sigma 85 f1.4 -4
Sigma 24-70 @ 70 -2

K-3II
DFA 150-450 @450 +10 (I suspect the result would be better at +11 or +12)
Sigma 85 f1.4 +7
Sigma 24-70 @70 -2

So given the above, if I were to make an adjustment in debug mode, what level of adjustment should I apply to K-3II and to the K-1?
Is there a reference or a link to how one uses debug mode?

Cheers,
Terry
09-29-2019, 11:19 PM   #18
Site Supporter
Site Supporter
vector's Avatar

Join Date: May 2015
Location: Alberta
Posts: 181
QuoteOriginally posted by tduell Quote
K-1
DFA 150-450 @450 +10
Sigma 85 f1.4 -4
Sigma 24-70 @ 70 -2
Here your max of +10 and low of -4 means you could add up to 6 steps to the current value in debug mode and still keep all your lenses within the AF fine tune range.


QuoteOriginally posted by tduell Quote
K-3II
DFA 150-450 @450 +10 (I suspect the result would be better at +11 or +12)
Sigma 85 f1.4 +7
Sigma 24-70 @70 -2
Here your max of +10 and low of -2 means you could add up to 8 steps to the current value in debug mode and still keep all your lenses within the AF fine tune range.

As mentioned in the other thread, make note of the value that it came with from the factory so you can always set it back. Then just push it a couple steps and test. You are at +10 and need to go higher so you would add steps. Once you get it far enough to work with your 150-450 you would need to adjust the AF fine tuning for every other lens you own by the same number of steps since you are moving the centre line or 0 so to speak. For example your 85mm on the K3II is at +7 now. Say you added 30um, or 3 steps to get your 150-450 working, you would then decrease the adjustment for the 85mm from +7 down to +4 to keep it dialed in correctly since those 3 steps were added to the global debug adjustment.
09-30-2019, 03:22 AM   #19
dlh
F.O.G. (fat old geezer)
Loyal Site Supporter
dlh's Avatar

Join Date: Nov 2015
Location: Northern Piedmont of Virginia
Posts: 1,076
Interesting observation, and as subsequent posts indicate, subject to question. So here's the question: why do you feel that the area within the sharpest part of the scale on an angled surface is different from front to back? Is this physics, or anecdotal observation?

No question, by the way, that the newspaper on the wall method would work, and may be best. Problem is that I don't know why, and I'm hoping you can explain your rationale.

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 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.


09-30-2019, 03:31 AM   #20
Site Supporter
Site Supporter




Join Date: Feb 2015
Photos: Gallery | Albums
Posts: 7,105
QuoteOriginally posted by pschlute Quote
At the distances people use to generally AF/FA that is not correct. DOF is more 50/50 at close distance
DoF gradient doesn't change with distance. It's just that the eye can't quite distinguish how much DoF is in front and back.

---------- Post added 30-09-19 at 12:45 ----------

QuoteOriginally posted by stevebrot Quote
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.
Thanks for the link. Yes that is a good think to have the image plane parallel to the sensor plane. Interesting on my D-FA28-105, the reproducibility error of AF is larger than the variation induced by changing AF fine tuning values. There is a significant gap of sharpness depending on the lens AF initial condition before focusing (two initial conditions: pre-focus at infinity or pre-focus at nearest distance). That gap is minimum at AF fine tune = 0, and that gap increases at AF fine tune values other than 0. According to the statistical mean of errors over repeated AF trials, I should set my AF fine tune value to -6, but at that setting I'd get the best and worse images depending on initial condition. For my D-FA28-105, the AF tune = 0 setting doesn't give the best possible sharpness for one image taken separately, but that setting is what give the least dispersion of sharpness for any pre-focus condition and at every focal length. I could get more sharpness out of my D-FA28-105, but I'd need to pre-focus at infinity before every new shot I'd take.

---------- Post added 30-09-19 at 12:48 ----------

QuoteOriginally posted by dlh Quote
why do you feel that the area within the sharpest part of the scale on an angled surface is different from front to back? Is this physics, or anecdotal observation?
It is difficult to appreciate where the center of focus precisely is because of the continuous nature of the blur. I remember having adjusted a lens to nail focus on a tilted ruler, which later happen to not deliver the best sharpness on a flat newspaper perpendicular to camera-lens axis.

Last edited by biz-engineer; 09-30-2019 at 03:52 AM.
09-30-2019, 06:56 AM   #21
Loyal Site Supporter
Loyal Site Supporter
pschlute's Avatar

Join Date: Mar 2007
Location: Surrey, UK
Photos: Gallery
Posts: 3,577
QuoteOriginally posted by biz-engineer Quote
DoF gradient doesn't change with distance. It's just that the eye can't quite distinguish how much DoF is in front and back
But when i plug anything 25 feet or less into a DOF table it tells me DOF is 50/50 front back. My own eyes tell me the same when i do an AF/FA test
09-30-2019, 07:30 AM   #22
dlh
F.O.G. (fat old geezer)
Loyal Site Supporter
dlh's Avatar

Join Date: Nov 2015
Location: Northern Piedmont of Virginia
Posts: 1,076
QuoteOriginally posted by biz-engineer Quote
... Interesting on my D-FA28-105, the reproducibility error of AF is larger than the variation induced by changing AF fine tuning values. There is a significant gap of sharpness depending on the lens AF initial condition before focusing (two initial conditions: pre-focus at infinity or pre-focus at nearest distance). That gap is minimum at AF fine tune = 0, and that gap increases at AF fine tune values other than 0. According to the statistical mean of errors over repeated AF trials, I should set my AF fine tune value to -6, but at that setting I'd get the best and worse images depending on initial condition. For my D-FA28-105, the AF tune = 0 setting doesn't give the best possible sharpness for one image taken separately, but that setting is what give the least dispersion of sharpness for any pre-focus condition and at every focal length. I could get more sharpness out of my D-FA28-105, but I'd need to pre-focus at infinity before every new shot I'd take.
...
It is difficult to appreciate where the center of focus precisely is because of the continuous nature of the blur. I remember having adjusted a lens to nail focus on a tilted ruler, which later happen to not deliver the best sharpness on a flat newspaper perpendicular to camera-lens axis.
I'd noticed the same effect, so when I do calibration, I generally do about ten images at the same degree of rectification, but alternating each shot's initial focus position from "lock to lock". I then sort of average the observations in a rough perception sort of way (after all, it's what looks best to me that counts rather than any kind of scientific or mathematical calculation) to get the proper offset in the fine-tuning menu. Essentially the same method as I'd use to adjust the sights on a handgun, which is essentially like interpreting the central tendency of the clusters of dots in a scatter-plot graph (what the gun-folks call "groups").

I've been using a two-foot carpenter's level, graduated as a ruler on one side and with a big black "magic marker" dot at the twelve-inch point as my calibration target. I lay it flat on a table with the ruler side up, and take the pictures from an angle (as a practical matter, at a random angle, but always less than forty-five degrees - probably more like fifteen or twenty). I've found that, while the blurred area varies continuously, it varies from most-blurred to most-sharp equally on either side. I use that to determine where the most-sharp point is, by finding the equally blurred numbers on either side of the most-sharp point, on the assumption that my (old astigmatic and nearsighted) eyes can't really detect the most-sharp point from the most-nearly-sharp point. So when the numerals "10" and "14" are equally blurred, then the lens is properly calibrated. Works for me so far, but I think I'll try your newspaper on the wall technique as an experiment.

Example from my usual technique:
Attached Images
View Picture EXIF
PENTAX K-1  Photo 

Last edited by dlh; 09-30-2019 at 09:20 AM.
09-30-2019, 09:40 AM - 1 Like   #23
Site Supporter
Site Supporter




Join Date: Feb 2015
Photos: Gallery | Albums
Posts: 7,105
QuoteOriginally posted by pschlute Quote
But when i plug anything 25 feet or less into a DOF table it tells me DOF is 50/50 front back.
Approximately true. For example, 70mm f2.8, 25 feet => front Dof = 43% , Dof back Dof = 57%. And that Ok for most of us. But for some people looking after those calibration I'm afraid approximately 50% isn't good enough. You see the challenge when you realize that lens AF repeatability lies between +-5 within the range of AF fine tuning adjustment! You have to take 30 shots so that the average shots are in near perfect focus. That's why the AF cal. software needs many shots to compute a fine tuning value... That's only for one focal length for a zoom, now imagine the AF offset drift away when you zoom in and out. We would need to enter a look up table that contain, for a particular copy of a zoom, an AF fine tune value for each focal length of the zoom (or some kind of in-camera interpolation based on correction values for the min, mid, and max FL of the zoom). Life is hard in sharpness territory.

09-30-2019, 11:25 AM   #24
Loyal Site Supporter
Loyal Site Supporter
pschlute's Avatar

Join Date: Mar 2007
Location: Surrey, UK
Photos: Gallery
Posts: 3,577
QuoteOriginally posted by biz-engineer Quote
Approximately true. For example, 70mm f2.8, 25 feet => front Dof = 43% , Dof back Dof = 57%.
Agreed , it will only get to 50/50 when very close.

QuoteOriginally posted by biz-engineer Quote
But for some people looking after those calibration I'm afraid approximately 50% isn't good enough
Disagree here. I accept it is a visual eyeball thing, but in your original post you claimed that DOF was 1/3- 2/3. It is not when using a distance that most folk will to calibrate their lenses. It may not be exactly 50/50 but is is a lot closer to that than 1/3 2/3 ! A simple visit to a DOF calculator will demonstrate.

i understand the intricacies of AF/FA. I have 14 lenses that I have tuned. I just wanted to make sure folk were not sent down the wrong path when looking at their test pictures
09-30-2019, 08:09 PM   #25
Loyal Site Supporter
Loyal Site Supporter
UncleVanya's Avatar

Join Date: Jul 2014
Photos: Gallery | Albums
Posts: 15,744
The 1/3 front 2/3 back is more of a hyperfocal technique than a dof truth I thought. I have focused to take advantage of it in the past but never expected it to play a role in critical lens focus tuning.
09-30-2019, 10:42 PM   #26
Site Supporter
Site Supporter




Join Date: Feb 2015
Photos: Gallery | Albums
Posts: 7,105
QuoteOriginally posted by pschlute Quote
Disagree here. I accept it is a visual eyeball thing, but in your original post you claimed that DOF was 1/3- 2/3. It is not when using a distance that most folk will to calibrate their lenses. It may not be exactly 50/50 but is is a lot closer to that than 1/3 2/3 ! A simple visit to a DOF calculator will demonstrate.
Yes, you are right, 53/57 is close to 50/50. I ran 60 test shots with my DFA28-105, with sharpness quantified for each image, for the mean value I obtained a kind of bell curve with two shoulders beside the default manufacturer settings. So the maximum sharpness is not obtained with the default setting, BUT the default factory does give the least deviation of sharpness regardless of initial lens AF conditions (pre-focus far or near), which is now totally understandable for me.

So, it's a personal choice:
- Do I want to use the default factory setting and have 99% of my images in good but not best focus?
- Or do I want to tweak my AF so that to have 50% of my images with maximum sharpness at one focal length at one focus distance and the rest of my photos less sharp then with default factory settings?

Personally, I prefer to have a little less sharp images, but that all of them are acceptably sharp. If I took a photograph for a very high value project for which I want to have the maximum sharpness, I'd focus in live view and use electronic shutter.

---------- Post added 01-10-19 at 07:57 ----------

QuoteOriginally posted by UncleVanya Quote
The 1/3 front 2/3 back is more of a hyperfocal technique than a dof truth I thought.
It is funny how DoF can be manipulated to serve an own opinion. For when deciding where to focus in a frame , the 1/3rd 2/3rd DoF rule applies, but for AF tuning we should use 50/50 at close distance?
We have a little problem here... aren't we supposed to tune AF for best results in actual shooting conditions? Or we tweak AF at 4 feet distance that we will almost never use when taking photographs outdoors?
How much of the AF calibration performed at 4 feet (~1 meter) will still work when shooting subjects between 20 and 40 feet (~5 to 10 meters)?

Last edited by biz-engineer; 09-30-2019 at 10:59 PM.
10-01-2019, 04:08 AM - 1 Like   #27
dlh
F.O.G. (fat old geezer)
Loyal Site Supporter
dlh's Avatar

Join Date: Nov 2015
Location: Northern Piedmont of Virginia
Posts: 1,076
Well, you've seen my highly technical implement pictured below; that's not the end of the story, of course. What that does is give me "initial operational capability". Experience taking pictures will tell me if it needs further adjustment. And to continue my "adjusting the sights" metaphor, what I'm trying to do is adapt the camera to me and the way I want to use the camera. Too many people try to adapt themselves to their camera rather than the other way around. It's my own vision that's what's really important, not a #(*$@(#*& camera! So I don't regard either the angle of the target or whether the camera's exactly horizontal, or what distance I'm using as particularly important. It's possible to get too wrapped up in the technical stuff and lose sight (pun intended) of the vision.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
adjustment, af, alignment, autofocus, body, condition, distance, dof, dslr, fa*, focus, full frame, full-frame, gap, k-1, k1, lens, lenses, pentax k-1, results, setup, sharpness, soft
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
AF Fine Adjustment question TerryL Pentax SLR Lens Discussion 14 05-02-2019 02:28 AM
AF Fine Adjustment Jim93 Pentax K-70 6 11-26-2018 11:41 AM
Fine Adjustment for AF Points Away From Centre? BruceBanner Photographic Technique 10 09-05-2018 02:01 PM
All lens needs AF fine adjustment, does the camera need a global adjustment? Thanks bennyxyz Troubleshooting and Beginner Help 9 04-21-2016 12:36 PM
AF Fine Adjustment, focus correction, AF micro adj., AF fine tuning annajonna Pentax K-5 13 11-19-2011 11:32 PM



All times are GMT -7. The time now is 07:46 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top