The test set-up
See the picture below.
Remember that the set up shown here is for information only. Bank-notes are not mandatory. They were used here for fun.
Any background with distinctive features or pattern shall fit.
Some EURO bills are arranged (each vertically on its side) in a circle around the front of the CP990 fisheye lens.
At mid distance, some sharpened nails are vertically pinned down on a blank sheet of paper. Check the vertical with a Square.
The Optical Axis of the lens is projected and drawn also on the paper as a straight line. Use of a Square for that purpose is recommanded.
Next : The experimental process