Testing astronomical optical standards of locally made parabolic mirrors for Newtonian Reflecting Telescopes

Abstract

A study of mirror making was initiated with the aim of designing a Newtonian reflecting telescope. Parabolic mirror of 15 cm aperture and 1.49 m focal length was made utilizing two identical Soda-lime glass disks. One side of a flat glass disk (one selected for the mirror) was grinded into the parabolic concave shape using series of Silicon Carbide (SiC) and Aluminum Oxide (Al2O3). The grinded mirror was polished using Pitch (Phenols, Polycyclic aromatic hydrocarbons) and Ferric Oxide (Fe2O3). Focal length of the mirror was measured after each grinding process. Uniformity of the concave shape figured in the mirror was tested using Foucault knife-edge test. Deviations from the required parabola were investigated by employing Millies-Larcroix method. It was found that the parabolic shape of the glass is satisfying astronomical optical standards confirming the quality of mirror prepared by this method.