Wide angle lenses calibration with Opencv

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I'm using a wide-angle lens (178º Diagonal FOV ) and I'm trying to calibrate it properly using Opencv Calibration module. All the detection and calibration process are working fine, but the result is very poor.

I have tried many different configurations:

• Different set of images
• Different radial coefficient numbers: 2,3,4,5 even 6.(CV_CALIB_FIX_K1,...,CV_CALIB_FIX_K6 )
• Fixing principal point and tangential disortion to 0 (CV_CALIB_FIX_ASPECT_RATIO, CV_CALIB_FIX_PRINCIPAL_POINT)
• Using expected focal length as initial camera matrix. (CV_CALIB_USE_INTRINSIC_GUESS)

The best I can get is something like:

Any ideas about how could I get a good calibration? Do you think using two calibrattion patterns at the same time, or using a circles grid as calibration pattern would help?

I've tried as well the opencv 3.0 thin prism coeffs, but they didn't help.