Sziasztok Skacok

Chapter 2

Mirror Design For Optical Telescopes

The reflector mirror is the most important component of an astronomical optical telescope. This chapter provides discussions on the requirements for astronomical optical mirrors; the ways to reduce mirror weight, mirror cost, and mirror materials; the methods of mirror figuring, polishing, and surface coating; the design of mirror support mechanism; the concept of mirror seeing; and the stray light control. Emphasis is placed on various mirror designs for modern large optical telescopes. These include the thin mirror, honeycomb mirror, segmented mirror, and multi-mirror telescope concepts. When discussing all these concepts, important formulas and their restrictions are provided for the reader’s reference so that they may use them in their mirror design practice. The discussion on the mirror support system is thorough and comprehensive, including both the positional and flotation support systems. A new mirror support system using a hexapod platform is also introduced. In the stray light control section, a new scattering theory based on the bidirectional reflectance distribution function is also introduced.

2.1 Specifications for Optical Mirror Design
2.1.1 Fundamental Requirements for Optical Mirrors An optical astronomical telescope, as a very sensitive light collector, comprises a number of important components. Among these, the reflecting primary mirror is the most important. The telescope efficiency is directly related to its area, its reflectivity, and its surface accuracy. The mirror area and reflectivity have been discussed in Section 1.2.2. The mirror surface accuracy is related to wavefront errors which affect the image Strehl ratio. The image Strehl ratio and the wavefront error were briefly introduced in Section 1.4.3. To obtain sharp star images, a rigorous tolerance is used for the mirror surface precision. The ideal primary mirror shape is determined through optical design, ray tracing, and

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