My calibration setup: a square chessboard on the wall(outdoor), the camera was held by hand and take pictures from different view.

the first calibration gives:

camera matrix
4036.306897 0.000000 627.648230
0.000000 4046.875620 370.241373
0.000000 0.000000 1.000000

distortion
-0.410160 -1.105400 -0.005716 0.002621 0.000000

while the second gives:

camera matrix
4046.339746 0.000000 692.904718
0.000000 4058.010391 368.021828
0.000000 0.000000 1.000000

distortion
-0.396681 -1.172958 -0.005052 -0.003120 0.000000

These results obviously differ much. I am quite confused.

BTW, I found that the skew bar could hardly make any progress during the calibration, even the view angle was larger than 45 degree. What's more, the chessboard couldn't be recognized with larger view angle.