ABSTRACT
The function of a telescope is to collect astronomical radiation and direct it into an instrument for further manipulation and detection. This chapter outlines the physical optics considerations that dictate the performance of telescope systems. It describes the most commonly used telescope configurations and the optical principles underlying telescope optics, before considering imperfections from aberrations and diffraction. The chapter shows that other approaches using Fourier optics can enhance our understanding of instrument design and provides valuable tools for designing and analysing telescopes. Most modern astronomical telescopes use a reflective mirror as the primary optical element. Instruments can have mirrors or lenses or both. The chapter considers the basic properties of both, starting by considering the refractive properties of a thin plano-convex lens with a spherical surface, of radius R, for rays near the optical axis. Coma is an aberration associated with object points away from the optical axis.
