Optical configuration for the four-mirror Nasmyth focal reducer to convert the Nasmyth f/13.5 focus into an f/3.0 focus to permit scale and optical speeds typical of the prime focus. The field of view is 8 min of arc.
Spot diagrams for the f/3 reducing camera at several field angles and wavelengths. The slight color aberration arises from the field lens. No plane–parallel window ahead of the focal surface is included in these diagrams.