[ablundon]

I was responding to another thread about a wish list of improvements for the K-3 and I stared wondering about focus calibration.

Would it be possible to (it would obviously have to be a firmware update) to get the camera automatically calibrate the Phase Detection AF system using the Contrast Detection system (i.e. Live View). From my understanding, Contrast Detection AF is usually pretty accurate and the calibration settings only adjust the phase detection (from what I understand - please correct me if I'm wrong).

I would see it working like this:

1. Set the camera up on a tripod
2. Set up a fixed focus object (flat so that there is no error introduced by curves/angles)
3. Set the camera to "Automatic Calibration Mode"
4. The camera would switch to Phase Detection attempt to focus.
5. When focus is achieved it would automatically switch to Contrast Detection and check to see if moving the focus ring decreases focus. If it does, it would automatically adjust the calibration.
6. Repeat until the focus achieved in Phase Detection requires no adjustment in Contrast Detection.

Would this work or am I off my rocker?

AB

[percy]

Sounds perfectly reasonable to me

[AldaCZ]

I have been thinking about the same( I do the same. I use PD, then I do a check via LV..)

[nomadkng]

This would be awesome if not for the technological hurdles.

The camera and lens would need a PID loop such that the camera knew to the mm the focus distance of the lens for test A. The camera would then have to use fuzzy logic to determine if increasing or decreasing the focus distance created a more "in focus image". The camera would then have to conclude where the best image was and compare that to the original focus lock. Finally the camera would then have to translate that into front/back focus correction. All this while actually taking over the automated focus process.

That would be a massively complex computer program.

My suggestion would be to allow the front/back focus adjustments to be seen in real time. Would go something like this:

Human presses focus button, PDAF gives focus lock on a calibration chart. Human presses "Focus Review" which locks focus mechanism and aperture at wide open and transitions to LV. Human can then Zoom in LV to 100% and adjust for front or back focus in real time. Since I believe this actually shifts the sensor forward or backward you would see real time feedback at 100%. Human then selects "Focus Test" and PDAF cycles the lens to infinity then min and then attempts focus lock. Human then presses "Focus Review" and checks results in LV. Repeat as necessary until lens is calibrated.

That would be a MUCH simpler program I believe because you would not be using CDAF, just implementing LV mode and access to front/back focus adjustments. You would also be interlocking the focus mechanism which I believe is already in place to some degree, and if not, should be a simple mechanical implementation.

[ruben]

As fixed focus object I use a lenscal (spyder). With the scale on it it's easy to control the focus point. Loading the image into the computer to see it in big makes it neat.

[ablundon]

Human presses focus button, PDAF gives focus lock on a calibration chart. Human presses "Focus Review" which locks focus mechanism and aperture at wide open and transitions to LV. Human can then Zoom in LV to 100% and adjust for front or back focus in real time. Since I believe this actually shifts the sensor forward or backward you would see real time feedback at 100%. Human then selects "Focus Test" and PDAF cycles the lens to infinity then min and then attempts focus lock. Human then presses "Focus Review" and checks results in LV. Repeat as necessary until lens is calibrated.

This sounds like it could also work and wouldn't be that hard to implement.

I'm not quite sure though that an automatic process would be that complicated. For PDAF I assume the camera must keep track of the screw/HSM motor as PDAF is a predictive AF system (from what I understand). PDAF attempts to guestimate how much out of focus an image is and then sends the signal to the AF motors to operate for a certain amount of time or rotations to attempt to achieve focus. Once the motors finishes it checks again and then if any minute adjustments are needed and then (if needed) sends the signal to the motors again. That's why there is always one or two stages to PDAF focus. (Again I could be wrong here).

So if the camera is able to keep track of the position of the motor for focus then the process could work like this. Human sets camera to Focus Calibration mode. The camera focuses on an object using PDAF. The camera then switches to Live View. The camera then increases focus by a fixed amount and then decreases by a fixed amount constantly reviewing the contrast of the image. It then can determine where the contrast is the sharpest and then makes note of the position of the motors relative to where they were during the PDAF. If they are different then adjust the calibration and repeat until there is no difference in the position of the motors.

I wouldn't think this would be a complicated program especially for Pentax. I would think the programming required to shift the sensor for Astrophotography would be equally as complex.

Alternatively another method would be for it to simply step through the 20 levels of calibration one at a time and determine which works best. The camera would start at -10, use PDAF capture the image. Then switch to -9, use PDAF and again capture. Repeat until +10. Then review all of the images using the CDAF engine to see which one is sharpest and there you go. It is more of a trial and error approach but would also work with much simpler programming.

[GlassJunkie]

I was responding to another thread about a wish list of improvements for the K-3 and I stared wondering about focus calibration.

Would it be possible to (it would obviously have to be a firmware update) to get the camera automatically calibrate the Phase Detection AF system using the Contrast Detection system (i.e. Live View). From my understanding, Contrast Detection AF is usually pretty accurate and the calibration settings only adjust the phase detection (from what I understand - please correct me if I'm wrong).

I would see it working like this:

1. Set the camera up on a tripod
2. Set up a fixed focus object (flat so that there is no error introduced by curves/angles)
3. Set the camera to "Automatic Calibration Mode"
4. The camera would switch to Phase Detection attempt to focus.
5. When focus is achieved it would automatically switch to Contrast Detection and check to see if moving the focus ring decreases focus. If it does, it would automatically adjust the calibration.
6. Repeat until the focus achieved in Phase Detection requires no adjustment in Contrast Detection.

Would this work or am I off my rocker?

AB

I printed out Yvons' lens charts from the K-3 eBook, laminated to shirt cardboard, etc... They work VERY well. First 2 DA*s good (16-50 and 60-250). more to come... We'll see...

http://www.ebooks4cameras.com/Pentax-K-3-e-book-NOW-AVAILABLE-K-3.htm (Link)

[dadipentak]

I'm glad to see this concept getting a some traction. Sure, there are technological hurdles but that's the game these days--right? I mean, I wandered in here from the 20th century and I'm blown away by the technological hurdles that had to be cleared to produce the K-3. Know what I mean?

[stevebrot]

Yes, this is possible. I would imagine using something similar to the Dot Tune method.

For owners of many Nikon and Canon cameras there is the Reikan FoCal software that provides automated focus calibration on a tethered camera.

Reikan FoCal Automatic Lens Calibration Software | Fully Automatic Lens Calibration and Camera ToolsReikan FoCal Automatic Lens Calibration Software

Pretty cool.

Steve

[ablundon]

Yes, this is possible. I would imagine using something similar to the Dot Tune method.

For owners of many Nikon and Canon cameras there is the Reikan FoCal software that provides automated focus calibration on a tethered camera.

Reikan FoCal Automatic Lens Calibration Software | Fully Automatic Lens Calibration and Camera ToolsReikan FoCal Automatic Lens Calibration Software

Pretty cool.

Steve

I tried this Dot Tune method tonight... unfortunately my room was too dark to get a reliable focus with LV. I tried anyway. With my Tamron 70-200 2.8 I was getting the focus dot to show up at -10 to +3. Unfortunately with -10 still showing in focus you really don't know where the bottom end is. Too bad Pentax didn't offer a bigger range on the focus calibration values.

That FoCal tool seems neat... unfortunately they don't support Pentax (which I guess is due to Pentax's lack of tethering support).

AB

[stevebrot]

I tried this Dot Tune method tonight... unfortunately my room was too dark to get a reliable focus with LV. I tried anyway. With my Tamron 70-200 2.8 I was getting the focus dot to show up at -10 to +3. Unfortunately with -10 still showing in focus you really don't know where the bottom end is. Too bad Pentax didn't offer a bigger range on the focus calibration values.

That FoCal tool seems neat... unfortunately they don't support Pentax (which I guess is due to Pentax's lack of tethering support).

AB

I had mixed luck with Dot Tune when I tried it on my K-3, though in principle it should work really well and would be the obvious way to do an automated calibration. Too bad that Pentax does not support tethering nor is there a published programming interface (API). Perhaps this will change when the tethering software for the 645Z comes out in the near future.


Steve

Hi folks,

I saw this twee about a lens calibration tool.

I never even thought about calibrating my lenses, but now I'm interested:

Focus Pyramid: Auto Focus Lens Calibration Tool | j.cristina

Cheers,
Keebler

PS. I've no affiliation with JCristina. Just interested in the calibration.