Anastigmat

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An anastigmat is a camera lens designed to be free from three main optical problems that blur images: spherical aberration, coma, and astigmatism. By using several lens pieces aligned in groups, these lenses can produce sharp pictures across the whole frame, not just in the center.

The term showed up in the late 19th century as makers advertised this new level of correction. The first true anastigmat was designed by Paul Rudolph for Carl Zeiss in 1890 and called Protar. It was improved quickly, becoming a five-element two-group design in 1891. In 1892 Emil von Höegh created the Dagor for Goerz, a symmetric six-element two-group lens. Around 1893–1895, Steinheil and Voigtländer developed similar six-element designs, and Rudolph released the larger Double Protar.

Another famous early line was the Cooke Triplet, designed by H. Dennis Taylor in 1893. It was three elements in three groups and cheaper to manufacture, which helped its popularity. J. H. Dallmeyer released the Stigmatic in 1895, initially with many elements and later simplified. Zeiss gradually moved away from the original Anastigmat designs toward newer types like Unar and Tessar in the early 1900s. The Tessar, introduced in 1902, became a long-lived standard as a four-element, three-group lens.

Other important families included the Dagor’s continued development, Goertz’s dialyte types leading to Artar, and the Plasmat from Hugo Meyer. The Cooke company also inspired related designs such as the Voigtländer Heliar, Ludwig Bertele’s Ernostar, and Zeiss’s Sonnar.

Today’s high-quality lenses are all close to anastigmatic in their ability to deliver sharp images across the frame, but they still have limits. They perform best at certain apertures and focusing distances. Aberrations still grow stronger toward the edges, though using multiple lens elements and sometimes aspheric surfaces helps. In telescopes, three-mirror anastigmat designs are common, while catadioptric systems combine mirrors and lenses to achieve similar results.