The alignment of a telescope consisting of 2 or more mirrors with powered surfaces is critical to system performance.
For on axis images, secondary mirror tilt and decenter both predominately produce coma, and therefore, either can be
used to correct coma. Consequently, for systems that operate over relatively narrow fields of view, it is not necessary to
differentiate between secondary tilt and decenter. However, for systems utilizing wider fields of view, correcting tilt with
decenter (or decenter with tilt) can result in large aberration variation off-axis. Details of a technique for differentiating
between secondary mirror decenter and tilt through the use of off-axis wavefront sensing, aberration calculation, and
alignment sensitivity modeling are presented.