Change in Intrinsic Parameters

Hi

I am new to computer vision. I am trying to calibrate my camera (Logitech C922 Pro) using camera calibrator app R2018b . I am using a checker board pattern. I calibrated it twice. With same checker board patteren. The Intrinsic parameter matrix came out different both times. Specially the focal lengh of the camera. The only change I made was the distance of the checker board from the camera.

I am doing all this to get the intrinsic parameters of the camera as its unknown. I need to use it for another application. Any one can guide? The camera have auto focus if it can cause the issue.

Answer 1

[Matt J]

Auto-focus seems like a highly probably explanation. If the focal length is physically changing, then the calibration code is doing its job by detecting those changes.

If you can turn the autofocus off and repeat the test, that should tell you something. Also, you should always do post-verification of the calibration, as discussed here,

https://www.mathworks.com/help/vision/examples/evaluating-the-accuracy-of-single-camera-calibration.html