Optics
The primary mirror is the Newtonian reflector's main light-collecting optical component. The 600 mm parabolic mirror is made from SCHOTT SUPREMAX 33 and optically figured by AstroReflect. The completed optic has been verified interferometrically and carries a high-reflectivity ZAOT SAP-EH coating.
At a glance
Substrate
The mirror is made from SCHOTT SUPREMAX 33, a borosilicate glass of type 3.3. Its low thermal expansion makes the material well suited to precision optics where dimensional stability under changing temperature is important.
SCHOTT specifies a linear coefficient of thermal expansion of 3.25 × 10⁻⁶ K⁻¹ over 20–300 °C. The material has a density of 2.23 g/cm³ and a thermal conductivity of 1.2 W/(m·K).
Figuring
The mirror blank was optically figured to a parabolic surface by AstroReflect. The finished mirror was subsequently verified interferometrically.
The measurement report gives a radius of curvature of 5,982.0 mm and a focal ratio of f/5. The measured best-fit conic constant is −1.008, compared with −1.000 for an ideal paraboloid. The report gives a Strehl ratio of 0.978 and an RMS wavefront error of 0.024 λ at 550 nm.
Surface
The finished mirror surface is coated with ZAOT SAP-EH, a high-reflectivity coating for astronomical optics.
Measured reflectivity is around 95% across much of the most relevant visual range, with approximately 95% at 500–600 nm and an average reflectivity of at least 89% over 400–700 nm.
