Anastigmat

Examples of anastigmat lens designs:
  1. Symmetric design by Emil von Höegh (1892) with six elements in two groups; marketed as the Double Anastigmat Goerz, aka Dagor, by Goerz.
  2. Asymmetric Zeiss Biotar double Gauss lens design by Willy Merté (1927), with six elements in four groups.
The controllable aperture stop is typically placed in the middle of the composite lens (between the so-called eye- and field-lenses), and its maximum diameter (the one shown) dictates the minimum F-number for each lens.

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 word Anastigmat in their name to advertise this new feature (Doppel-Anastigmat, Voigtländer Anastigmat Skopar, etc.).

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