Zeiss Sonnar
A lens design with relatively few glass-to-air surfaces, invented by Dr. Ludwig Bertele at Carl Zeiss in 1930 to provide the fastest lenses of that day for 35 mm photography offering speeds up to f/1.5 and well controlled veiling glare. This is where the name comes from, containig the German word for sun, 'Sonne', the symbol of utmost brightness. Since the PlanarŪ lens with its many glass-to-air surfaces could successfully take over the 'fastest lens' role from the SonnarŪ lens, after Dr. Alexander Smakula at Carl Zeiss invented anti-reflex coating in 1935, the SonnarŪ design turned out its other virtues. Today it is the basis for compact high-performance medium telephoto lenses with speeds up to f/2.8, very elaborate correction of lens errors (in the case of the SonnarŪ T* 5,6/250 CFi lens and the extreme case of the SonnarŪ Superachromat 5,6/250 CFE lens), incorporating expensive optical glass types, and offering very even corner-to-corner illumination.
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