Schneider Covertible 800mm f/12 Apo Tele-Xenar HM Telephoto Lens with Copal #3 Shutter.

The Apo-Tele-Xenar is a 5-element telephoto lens system with an angle of view of 35 degrees, which can be used with a focal length of 400mm for formats of up to 13cm X 18cm and with a focal length of 800mm for formats of up to 30cm X 40cm. The apochromatic correction, achieved by the use of special optical glass, gives a clear reduction in the secondary spectrum. The resolution of these special lenses is not sensitive at the normal working aperture to changes in the object to image ratio, with the result that the Apo-Tele-Xenar 5.6/400mm can be used without hesitation at a range of 2 meters. The gray surface of the mounting serves to reduce thermal effects. To avoid reflections and to improve transmission the Apo-Tele-Xenar has a multi-layer, anti-reflection coating.