The legend of three-element lens : Brief Introduction of Cooke Triplet



    Preface

    In 1983, British lens designer Harold Dennis Taylor (1862–1943) (hereafter “Taylor”) designed a 3-element lens consisting of two convex lenses and a concave lens (Cooke Triplet)[1], opening a new page in modern design of photographic lenses.

    Cooke Triplet Patent US568052 (includes variation)

    Features of the Cooke Triplet lens

    The triplet designed by Taylor are arranged in order of postive – negative – postitive. The focal power of the negative lens must be more or less equals to the focal power of the two postive lenses. The triplet has enough degrees of freedom for the lens designer to correct monochromatic aberrations(spherical, coma, astigmatism, field curvature) and chromatic aberrations(axial and lateral). Alternatively, apart from the simplest three-element design, the lens designer can replace any of the element with a glue doublet or splitting any of the element into multiple elements.

    Brit. Pat. 22,607

    When Taylor published his design in The Royal Photographic Society Journal, the maximum aperture was F3.7. Taylor mentioned that the lens designed was basically free of spherical aberration at F8, and the lens achieves best sharpness at F11. [2]

    The Royal Photographic Society Journal_Vol_35 p.75

    Because the company, T. Cooke and Sons, Taylor is working for were not interested in producing the triplet lens, Taylor bring his design to lens Taylor, Taylor & Hobson(“TTH”). TTH manufactured and sold the lenses under the name of “Cooke” which is the trademark of T. Cooke and Sons. Two series of Cooke Triplet were avalaible at the time of introdcution: Series II (Portrait lenses) and Series V (Process lenses). [3]

    Cooke Series II and Series V, The Royal Photographic Society Journal_Vol_39 p.28

    List of Cooke Triplet lenses for photography cameras

    When Taylor’s patent expired, other companies started to made their own triplet lenses. Here is a list of the lens series name made with Cooke Triplet design:

    Agfa: Agnar, Apotar
    Angenieux: Z
    Argus: Cintar
    Carl Zeiss Jena: Triotar
    Carl Zeiss Oberkochen: Pantar
    Corfield: Lumar
    Enna: Ennagon
    Hugo Meyer/Meyer: Trioplan, Domiplan
    Isco: Isoctar
    Kodak: Anaston
    LOMO: T
    Ludwig: Victar, Meritar
    Minolta: Rokkor TC
    Piesker: Piconar
    Rodenstock: Trinar
    Schacht: Travegar
    Schneider: Radionar
    Steinheil: Cassar, Cassarit
    …

    Other than photographic lenses, Cooke Triplet can also be found on enlargers such as Rodenstock Trinar/Rogonar and Schneider Componar/Componar-C. Moreover, the design were used on some projection lenses too such as Meyer Diaplan/Pentacon AV.

    Character of the common Cooke Triplets

    The two photos below are taken with Steinheil Cassarit 50mm F2.8 at s Sony NEX-5N. At F4.0, the contrast and sharpness are much better than at F2.8.

    Steinheil Cassarit 50mm F2.8 @F2.8

    Steinheil Cassarit 50mm F2.8 @F4.0

    List of Cooke Triplet lenses reviews which will be posted:

    Meyer Trioplan 100mm F2.8
    Leica Elmar 90/4.0 3e
    British APO triplet

    Reference:

    [1] Brit. Pat. 22,607 and US Pat. 568052
    [2] “A Simplified Form and Improved Type of Photographic Lens.” by H. Dennis Taylor https://archive.rps.org/archive/volume-35

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