Optical Specifications

Ritchey-Chretien
Aperture: 18 inches; Focal length: 189 inches
Focal ratio: f/10.5
Nominal mirror separation: 39.33 inches
Nominal back focal distance: 9.5 inches
Central obstruction: 7 inches

Primary Mirror
Diameter: 18 inches; Focal length: 54¼ inches
Nominal focal ratio: f/3
Central opening: 5 inches
Thickness: 2 inches; Weight: 40.5 pounds
Material: pyrex

Secondary Mirror
Diameter: 5 7/8 inches
Clear diameter: 5 ½ inches; Focal length: 19 ½ inches
Weight: 2 ¼ pounds
Material: Cervit