PHAROS optics elliptical secondary mirrors size range between 100 to 150 mm (short axis). These mirrors are intended for Newtonian telescopes and are custom made. This flexibility in size allows for an optimal design fit addressing telescopes intended for visual use or for Astro photography across a variety of focal ratios. The quality of a secondary mirror is even more important than that of the primary one. Optimized for excellent surface roughness the flatness is better than λ/10.  The coating is the same as for primary mirrors. It comprises highly reflective aluminium (> 96%)  that is protected by SiO2. An extra scratch-protection layer allowing easy cleaning is optional here as well. Every elliptical flat mirror, is uniquely tuned to its application and customer specification. It will be delivered with a test certificate.