The MMT7 Mirror: Analysis Of The Rms Difference Specifications And Their Impact On Fabrication And Testing

The figure-quality specifications for the seventh Multiple Mirror Telescope (MMT7) mirror were unusual in that they were defined in terms of rms differences. Recognizing that the atmosphere can be the limiting factor in telescope performance, the specifications for the MMT7 mirror, a 1.8-m, f/2.7 parabola, were derived from analysis of the wavefront irregularities induced by the atmosphere on a nominally perfect planar wavefront from a star. This approach to mirror specifications apparently was first taken with the 4.2-m Herschel Telescope primary mirror, fabricated at Grubb-Parsons.