Shack-Hartmann wavefront sensor versus Fizeau interferometer while optical surfaces testing

It is well known that to measure the aberrations of optical surface Fizeau interferometer could be used. Also very good solution is to test optics with Shack-Hartmann wavefront sensor. But we noticed that in case of strong aberrations of the surface under test the measured aberrations differ from the real ones. In the present work we used bimorph deformable mirror to reproduce strong aberrations and then measured these aberrations with both Shack-Hartmann wavefront sensor and Fizeau interferometer. The results of our experiments are discussed.