Cooke triplet lens

Definition: Standard lens design capable of giving good correction at low cost. * Consists of positive elements air-spaced either side of a bi-concave (therefore negative) element. * Evolved from anastigmat and Petzval design by H D Taylor for Cooke in 1893.
Close-up from Cooke
Quite a few modern lenses, particularly standard macro lenses, can trace their ancestry to the Cooke, via the classic Tessar designs -- themselves an elaboration of the Cooke triplet -- which were the mainstay of standard lens design for several decades. Tessars were noted for their excellent all-round correction and reasonable speed of f/2.8, yet were relatively inexpensive to manufacture. Another line of development from the Tessar gave us the classic Biogon and Sonnar families of high-performance optics.

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