A NOVEL SHEARING INTERFEROMETER WITH DIRECT DISPLAY OF LENS LATERAL ABERRATIONS

We describe a new shearing interferometer for lens testing which has h igh precision and direct display of lens aberrations. Shear is obtaine d by reflecting a wavefront collimated by the lens under test from the front and rear surfaces of a wedged glass plate. The surfaces of the plate are coated to increase their reflection coefficient and give sha rp multiple beam interference fringes which are easy to measure and in terpret. We show mathematically that the interference fringes map out the lateral aberration curve of the lens under test directly, and pres ent experimental results which display the advantages of this system o ver conventional two-beam shearing interferometers.