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

    留言

    發佈留言

    此網誌的熱門文章

    The Tiny All-rounder: Leica Elmar 90mm f/4.0 3-element Review

    圖片
    Table Of Contents ✓ Introduction Leica's first Elmar 9cm (90mm) f/4.0 was introduced in 1930. The lens construction was very similar to that of the Zeiss Tessar, with the main difference being that the Elmar had the aperture positioned in front of the second lens element. After several cosmetic changes, the optics of the popular Elmar 90mm lens remained unchanged until the early 1960s. In 1962, a new version of the Elmar 90/4.0 was released, designed by Walter Mandler in Canada using newly invented rare-earth glass, which elevated the performance of this classic lens to another level. Lens Versions There is only one version. It comes with either a Leica M mount (11830) or a Leica screw mount (11830). Leica Elmar 90mm f/4.0 3-element M mount Lens Specifications Lens mount: Leica M Focal length: 90mm Aperture adjustment: f/4.0–f/22 (with half-stop clicks) Number of aperture blades: 10 Minimum focus distance: 1 meter Filter size: E39 Hood: IUFOO or 12575 Weight: ~220g Leitz Sales...
    閱讀更多

    Techart TZM-02 Leica M to Nikon Z Autofocus Adapter Review

    圖片
      The second-generation Leica M to Nikon Z AF lens adapter TZM-02 from Techart will be officially released soon. I am fortunate enough to borrow this engineering sample for testing, let’s see how the autofocus performs. Table Of Contents ✓ Specification: Weight: ~150g Diameter: ～68mm *Compatible with all the latest Nikon Full Frame & APS-C camera models (Z9, Z7II, Z7, Z6II, Z6,Z5, Z50, Zfc, Z30, etc) *not applicable to LTM/M mount lenses with a infinity lock button near the lens mount In-Body Image Stabilization (IBIS) Settings By adjusting the aperture value, we can change the focal length value transmitted to the camera to obtain better image stabilization. The relationship between the aperture value and the focal length value transmitted is shown on the following table: Aperture Value(F) 1.0 1.1 1.2 1.4 1.6 1.8 2.0 2.0 Lens Focal Length(mm) 135 90 85 75 55 50 40 30 Aperture Value(F) 2.5 2.8 3.2 3.5 4.0 4.5 5.0 5.6 Lens Focal Length(mm) 28 25 24 21 20 18 16 ...
    閱讀更多

    Soap Bubble King: Meyer-Optik Görlitz Trioplan 100mm F2.8 Review

    圖片
    Sharpness is the most important factor of modern lenses as the pixel density of the sensor in digital cameras becoming higher and higher. With digital correction and good sharpness, the image captured by the camera become more perfect than ever. Is getting the perfect image our only requirement? Table Of Contents ✓ Introduction More than thirty years after Taylor Taylor invented the Cooke Triplet lens in England, Hugo Meyer & Co. in Görlitz Germany also began to manufacture and sell its Cooke Triplet lens series “Trioplan”. Here is the 1930 Lens Catalog from Meyer showing the details of the Trioplan lens series. Hugo Meyer Catalog (1930) p.8 In the beginning, the Trioplan lenses are made for 16mm and 35mm cine cameras, with focal length ranging from 15mm to 8¼”. The catalog mentioned the lens correction has been carried out for astigmatism, color and spherical aberration. By 1938, the aperture of the Trioplan series was standardized to F2.8, except for the Trioplan F2.5 made fo...
    閱讀更多