Abstract

The primary mirror for the W.H.T. has an aperture of 4.2 metres, and a focal ratio of f/2.5. The mirror blank is of glass ceramic (CER-VIT) with an edge thickness of 0.55 metre. While the mirror focal ratio and thickness are fairly conservative, the performance specification for the mirror is novel. The form of specification used is now generally accepted as providing a useful means of describing the performance of ground based telescopes, but as yet there is no operational experience with a large mirror made to a specification of this form. Before work started on the mirror it seemed probable that some changes in both working and testing methods would be needed if the quality requirements of the specification were to be achieved and demonstrated. This paper deals mainly with those aspects of fabrication and testing which were most affected by the form of specification.

© 1986 Optical Society of America