CaliBall is a 25.4mm-diameter silicon nitride ball and kinematics mount used to calibrate phase-measuring interferometers by determining the errors in the transmission-sphere reference surface. The CaliBall is randomly positioned with its center at the focus of the interferometer transmission sphere and aligned to better than one fringe. The calibration can be done in as little as 10 minutes. It works with any brand or make of transmission sphere and can be used to qualify a wide range of transmission spheres with F/#s ranging from F/0.7 to F/11 or beyond.
