A radial shear interferometer introduces radially symmetric shear by interfering the wavefront with an expanded copy of itself. A large shear gives similar results to a Twyman-Green interferometer, while small shear is a low sensitivity, high-dynamic-range test.
The resulting interferogram is the same as a Twyman-Green if each aberration coefficient is divided by 
, where n is the radial power of each particular aberration.
