Author Topic: Calibration Divergence  (Read 494 times)


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Calibration Divergence
« on: January 20, 2021, 04:30:21 PM »
Hello, I’m trying to calibrate my camera with the software for latter use in a project regarding Close Range Photogrammetry.
I'm confronting a Nikon D700 with a prime lens, against a newer Panasonic GX80 (MFT Mirrorless) with the kit zoom lens (H-FS12032).
I'm having a small divergence on the calibration results with the mirrorless and kit lens.
I suspect the problem could be with the sensor moving or the lens mechanism changing in between ON/OFF.

Camera Settings:
- MF (Then I go to the digital slider to set the focus position to the lowest value (for near subjects))
- Stabilizer OFF
- Aperture priority
- FN 13 for proper depth of field
- ISO 200
- Mechanical Shutter with 1 sec delay
- All fancy improvements (Intelligent Dynamics, Intelligent Resolution, Long Shutter Noise Reduction, Diffraction Compensation, Shadow Compensation) OFF

My workflow is as follow:

- I turn the camera on.
- Put it on a tripod.
- Shortest focal distance (12 mm) with the lens rig.
- Focus Position to the lowest (for nearby subjects)
- Select show Chessboard on the software and zoom out until the square size is 1 [mm]
- Shot with remote shutter (wifi) at least 100 photos changing the LCD position (inclination, tilt, depth) as much as possible in the range of depth (10 cm - 40 cm from the sensor mark)
- Convert the photos with Adobe Digital Negative Converter
- Upload the photos and calibrate the lens fitting all the parameters (f,cx,cy,k1,k2,k3,k4,p1,p2,p3,p4)
- Repeat 20 times
- Calculate the weighted mean and weighted std of the results from the calibrations sessions using as weight=(1/σ^2), assuming that the errors are equal to σ.

Cx,Cy,B1,B2,P3 and P4 diverge (evaluated on the weighted STD)

1)   Square size of the chessboard is too small? How does this influence the results?
2)   DNG vs TIFF I tried one set and the results changed a bit. Which format should I use?
3)   The assumption that the errors are equal to σ is OK? Are those Std OK (attachment file)?
4)   I tried fixing some parameters (f,cx,cy,b1,b2). Then I tried only the Image-Variant (f,cx,cy,b1,b2). Then I tried to combine them (fixing k1,k2,k3,k4 and Image-Variant f,cx,cy,b1,b2). Also I tried the rolling shutter compensation. I obtained the same results as before. I'm afraid that I'm doing something wrong here. Could you advice me on this?