Why are optical tolerances important for telescope mirrors?
No manufacturing operation performed by human beings has tolerances as demanding as telescope optics. The quality of a telescope mirror’s performance depends on care in its production, including the application of a meaningful tolerance for spherical aberration. By “meaningful” we mean that the tolerances used by the optician must have a direct correspondence to the expected level of performance in the telescope. The process tolerance should be designed to produce the smallest possible star image, in addition to minimizing microfinish and large-scale roughness. This will assure that roughness or edge problems will not create scattered light and loss of contrast at the wavefront.
