Distortion

If stabilization is unsatisfactory due to lens distortion effects then a basic lens calibration can be performed using the Distortion tool. Calibration requires the use of a test chart consisting of a grid of black on white filled circles. Such a chart can be generated using this website: https://calib.io/pages/camera-calibration-pattern-generator

To perform the calibration set the camera to maximum resolution (e.g. 5120x4096) at 24FPS. Film the calibration chart such that it just fills the field of view without any of the circles overlapping the edges. Make sure that the camera is aligned with the centre of the image and facing square on. A tripod or clamp of some sort is useful for this although it can be done freehand if desired. Only a few seconds of footage is necessary since the distortion tool will only look at one frame for performing the calibration.

Once the calibration clip has been taken, load the clip and select the Distortion tool. Check Enable and verify that all the circles are being detected correctly (green perimeters around each circle). Adjust brightness and contrast if necessary to detect all the circles. Scrub the clip if desired to find the best framing of the test chart.

Joining the grid circles together is a blue grid which should help visualise the extent of the lens distortion. The red grid overlaid on top should be perfectly rectilinear, indicating that the distortion is being identified and corrected.

The focal length must be set manually by entering the value in the Focal length entry. Use the value printed on the lens or given in the lens manual. Fine tuning of the focal length can be performed in the stabilizer if necessary.

The lens distortion parameters k1 and k2, together with the focal length and image resolution can be now saved in a calibration file for use in the stabilizer. Press Save calibration, navigate to the desired directory, enter a filename for this calibration and press Save.