A method is provided for reducing the piston of neighboring first and second
surfaces
illuminated by polychromatic light transmitted from an unresolved-light source
such that light transmitted or reflected from the first surface is out of phase
with light respectively transmitted or reflected from the second surface, and the
out-of-phase light is passed through a grism that generates a fringe pattern in
the far-field. According to one exemplary embodiment, the method includes Fourier
transforming the fringe pattern to generate a two-dimensional (2D) power spectrum;
generating the absolute value of the 2D power spectrum to form an absolute value
representation; displaying the 2D the absolute value representation on a computer
display; and reducing the piston to affect rotation of the absolute value representation
on the computer display and approximately align a central axis of the absolute
value representation with an axis that indicates approximate alignment of the first
and second surfaces.
