  An inadvertent or unwanted angular deviation to a passing beam can be
introduced by any single optical component within an optical system. The
problem arises due to an imperfect tilt alignment of the optical component or
manufacturing defects which results in a slightly different response than
expected from an ideally aligned/manufactured component. The resulting beam
deviation can plague any well-designed optical system that assumes the use of
ideal components. The problem is especially introduced by non-ideal lenses,
transparent plates and optical windows. Here we present a simple method of
manually introducing a deviation error angle which we assume to be constant for
all beam incidence angles over the paraxial range.
