Lens Data:

Focal Length: 500 mm
Optical Configuration: Off-Axis Makowsky - Cassegrain, patented design
Chromatic Aberration Correction: UV up to IR
IR Range: max. 4000 nm
Lens Elements / Groups: NA / NA
Mirror Elements / Type: 2 / ZEISS Schott ZERODUR, quartz sealed
Diaphragm Type: manual, stepless
Angle of View: 5° prime focus
Max. / Min. Aperture: f8 / 32
Clear Aperture: 42mm
Spherical Aberration: none
Chromatic Aberration: none, lateral and longitudinal
Coma On Axis: below diffraction limit
Diffraction Limit: < 4 micrometers
Curvature of Field: none
Image Lighting Fall Off: constant eveness over full field
Mirror Surface Precision: < 0.1 Lambda
Vignetting: none
Minimum Focus Distance: 4.9 m, 1.9 m for macro version EM
Filter Size: 67 mm
Lens Hood: built in
Length: 210 mm
Weight: 991 grams

(data + patent from company brochures)