MATLAB: Intrinsic Matrix using calibration app

Computer Vision Toolboxfocal lengthimage processingsingle camera calibration app

I'm calibrating my camera using single camera calibration app.However,I get different values of f_x (or f_y) for every trial I run.I take different sets of images for each trial.I do understand that f_x and f_y are not the same because of non square pixel but why does the value of f_x=F*s_x change for the same camera. Shouldn't the focal length in pixel dimension be constant for a given camera?From what I understand both F and s_x are constant.The variation is sometimes of 200 pixels between f_x-trail 1 and f_x trial 2.

Best Answer

"Shouldn't the focal length in pixel dimension be constant for a given camera"
Not generally, no. That would require a fixed focal length camera, not an adjustable focal length or auto-focus camera.
I have been up all night so I do not recall at the moment if the aperture affects the equation.
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