anastigmat

An anastigmat or anastigmatic lens is a photographic lens completely corrected for the three main optical aberrations: spherical aberration, coma, and astigmatism. Early lenses often included the German word in their name to advertise this new feature (, , etc.).

==History== ===Early designs=== thumb|left|upright=0.7|Carl Zeiss AG|Zeiss Protar (Rudolph, 1890) The first anastigmat was designed by Paul Rudolph for the German firm Carl Zeiss AG in 1890 and marketed as the Protar; it consisted of four elements in two groups, as an asymmetric arrangement of two cemented achromatic lens doublets and was improved to a five-element, two-group design in 1891, substituting a cemented triplet for the rear group.