August Köhler

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August Köhler
University of Heidelberg
  • University of Giessen
    • Known forKöhler illumination
    Awardshonorary doctor degree of the University of Jena
    Scientific career
    FieldsPhysicist
    Institutions
    Doctoral advisorJohann Wilhelm Spengel

    August Karl Johann Valentin Köhler (4 March 1866 – 12 March 1948) was a German professor and early staff member of Carl Zeiss AG in Jena, Germany. He is best known for his development of the microscopy technique of Köhler illumination, an important principle in optimizing microscopic resolution power by evenly illuminating the field of view. This invention revolutionized light microscope design and is widely used in traditional as well as modern digital imaging techniques today.

    Early life and education

    Köhler was born in 1866 in Darmstadt, Germany, where he attended the Ludwig-Georgs-Gymnasium until 1884. He studied at the Technical University in Darmstadt and at the universities of Heidelberg and Giessen covering a wide range of fields from zoology and botany to mineralogy, physics, and chemistry.[1]

    Teaching and academic career

    In 1888, August Köhler graduated with a teaching degree and subsequently taught at gymnasiums in Darmstadt and Bingen before going back to university. He started his academic career as a student, instructor and assistant to professor J.W. Spengel at the Zoological Institute at the university of Giessen, Germany. The object of his doctorate thesis was the taxonomy of limpets, a project that depended heavily on microscopic imaging and prompted Köhler into trying to improve the quality of images taken via photomicrography. The result of this work was published in 1893.[2]

    After receiving his

    doctorate degree from the University of Giessen in 1893, Köhler worked a number of years as a grammar school teacher in Bingen. In 1900, he was invited to join the Zeiss Optical Works company in Jena, Germany, by Siegfried Czapski based on his earlier work on improving microscope illumination. He stayed with Zeiss as a physicist for 45 years and became instrumental to the development of modern light microscope design. From 1922 until his retirement in June 1945, he was also professor for microphotometry at the University of Jena. He became honorary professor of the Medical Faculty at the University of Jena in 1922 and received an honorary medical doctor degree in 1934. In 1938, he assumed the head position for the Department of Microscopy, Microphotography and Projection.[1]

    Köhler illumination

    At the time of the invention of his revolutionary illumination scheme as a graduate student at the University of Giessen, Köhler was working on overcoming problems with microphotography. Microscopes were illuminated by

    epifluorescence, and confocal microscopy.[4]

    Köhler's groundbreaking work on microscope illumination was published in the

    Journal of the Royal Microscopical Society one year later.[6] Its significance was not noted until several years later when Köhler was invited to join the Carl Zeiss AG company based on his invention. A century after its first publication, a translation of Köhler's original article, A New System of Illumination for Photomicrographic Purposes, was reprinted in the Köhler Illumination Centenary commemorative issue by the Royal Microscopical Society in 1994.[7]
    Today, the Köhler illumination is considered one of the most important principles in achieving the best optical resolution on a light microscope.

    Other contributions to microscope development

    When Köhler joined Zeiss in 1900, Ernst Abbe and glass specialist Otto Schott had already paved the way for microscope improvements through their contributions to precise optical theory and the development of appropriate glass formulas. Köhler's expertise and his illumination technique helped to improve the microscope optics to achieve optimum resolution, using the entire resolving power of Abbe's objectives.

    Köhler remained an active staff member of Zeiss for 45 years, contributing numerous innovations during this time. These include the development of a microscope operating with

    parfocal lenses which allow the specimen to remain in focus when changing objectives on a microscope.[7]

    Patents and publications

    As a member of Zeiss, August Köhler filed at least 25 patent applications in Europe as well as at least ten patents in the USA. His patents include projection methods and illumination for

    United States Patent Office on 31 March 1925 (patent number 1649068).[9] His publications include essays on microscopy and projection systems, and in particular his specialty of microphotography. His contributions to biology include fine structure analyses of diatoms.[1]

    References

    1. ^ a b c d Zeiss Archives
    2. ^ Köhler A (1893). "Gedanken zu einem neuen Beleuchtungsverfahren für mikrophotographische Zwecke". Zeitschrift für wissenschaftliche Mikroskopie.
    3. doi:10.1007/BF01476460
      .
    4. ISBN 0-471-25391-X
    5. ^ Köhler, August (1893). "Ein neues Beleuchtungsverfahren für mikrophotographische Zwecke". Zeitschrift für wissenschaftliche Mikroskopie und für Mikroskopische Technik. 10 (4): 433–440.
    6. ^ Koehler, August (1894). "New Method of Illimination for Phomicrographical Purposes". Journal of the Royal Microscopical Society. 14: 261–262.
    7. ^ a b Pioneers in optics: August Köhler
    8. ^ History of optics in Jena Archived September 30, 2007, at the Wayback Machine
    9. ^ USPTO patent image database
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