Alan Ward and John Moon, MOONWARD Vacuum Coatings (Optical Coatings for Telescopes). Alan is interested in telescope making, and the promotion and teaching of telescope-making, through the art of grinding, polishing, and figuring of mirrors and lenses. John is interested in radio astronomy and has been involved with MOONWARD Vacuum Coatings from its inception in 1993, acting as a technical collaborator, having had previous experience with high vacuum.

Optical surfaces of all modern quality astronomical instruments are coated with very thin layers of metallic or dielectric materials to improve optical performance. This presentation will describe the theory of thin-film interference, and give an overview of what every telescope user should know about the many available optical coatings for mirrors and lenses.