August Köhler
Encyclopedia
August Karl Johann Valentin Köhler (March 4, 1866 – March 12, 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.
, 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
.
s 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 limpet
s, 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.
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.
s available at the time. Over the course of his work for his doctorate degree, Köhler developed a microscope configuration that allowed for an evenly illuminated field of view and reduced optical glare from the light source. It involved a collector lens for the lamp that allowed the light source to be focused on the front aperture
of the condenser. This in turn allowed the condenser to be focused on the specimen using a field diaphragm
and condenser focus control. This superior illumination scheme is still widely used in modern microscopes and forms the basis for phase contrast
, differential interference contrast
, epifluorescence, and confocal microscopy
.
Köhler's groundbreaking work on microscope illumination was published in the Zeitschrift für wissenschaftliche Mikroskopie in 1893 in Germany
, followed by an English summary of his work in the Journal of the Royal Microscopical Society one year later. 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. Today, the Köhler illumination is considered one of the most important principles in achieving the best optical resolution on a light microscope.
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 ultraviolet light (together with his colleague Moritz von Rohr
), pioneering what would become the starting point for fluorescence microscopy, and the discovery of grid illumination, a method that would later be used in the treatment of tumor
s. A suggestion by Köhler led to the development of parfocal
lenses which allow the specimen to remain in focus when changing objectives on a microscope.
s.
Jena
Jena is a university city in central Germany on the river Saale. It has a population of approx. 103,000 and is the second largest city in the federal state of Thuringia, after Erfurt.-History:Jena was first mentioned in an 1182 document...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
. He is best known for his development of the microscopy
Microscopy
Microscopy is the technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye...
technique of Köhler illumination
Köhler illumination
Köhler illumination is a method of specimen illumination used for transmitted and reflected light optical microscopy. Köhler illumination acts to generate an extremely even illumination of the sample and ensures that an image of the illumination source is not visible in the resulting image...
, 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 DarmstadtDarmstadt
Darmstadt is a city in the Bundesland of Hesse in Germany, located in the southern part of the Rhine Main Area.The sandy soils in the Darmstadt area, ill-suited for agriculture in times before industrial fertilisation, prevented any larger settlement from developing, until the city became the seat...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, where he attended the Ludwig-Georgs-Gymnasium until 1884. He studied at the Technical University in Darmstadt and at the universities of Heidelberg
Heidelberg
-Early history:Between 600,000 and 200,000 years ago, "Heidelberg Man" died at nearby Mauer. His jaw bone was discovered in 1907; with scientific dating, his remains were determined to be the earliest evidence of human life in Europe. In the 5th century BC, a Celtic fortress of refuge and place of...
and Giessen covering a wide range of fields from zoology
Zoology
Zoology |zoölogy]]), is the branch of biology that relates to the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct...
and botany
Botany
Botany, plant science, or plant biology is a branch of biology that involves the scientific study of plant life. Traditionally, botany also included the study of fungi, algae and viruses...
to mineralogy
Mineralogy
Mineralogy is the study of chemistry, crystal structure, and physical properties of minerals. Specific studies within mineralogy include the processes of mineral origin and formation, classification of minerals, their geographical distribution, as well as their utilization.-History:Early writing...
, physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, and chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
.
Teaching and academic career
In 1888, August Köhler graduated with a teaching degree and subsequently taught at gymnasiumGymnasium (school)
A gymnasium is a type of school providing secondary education in some parts of Europe, comparable to English grammar schools or sixth form colleges and U.S. college preparatory high schools. The word γυμνάσιον was used in Ancient Greece, meaning a locality for both physical and intellectual...
s in Darmstadt and Bingen
Bingen am Rhein
Bingen am Rhein is a town in the Mainz-Bingen district in Rhineland-Palatinate, Germany.The settlement’s original name was Bingium, a Celtic word that may have meant “hole in the rock”, a description of the shoal behind the Mäuseturm, known as the Binger Loch. Bingen was the starting point for the...
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
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
. The object of his doctorate thesis was the taxonomy of limpet
Limpet
Limpet is a common name for a number of different kinds of saltwater and freshwater snails ; it is applied to those snails that have a simple shell which is more or less conical in shape, and either is not spirally coiled, or appears not to be coiled in the adult snails.The name limpet is most...
s, a project that depended heavily on microscopic imaging and prompted Köhler into trying to improve the quality of images taken via photomicrography
Micrograph
A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an item.Micrographs are widely used in all fields of microscopy.-Photomicrograph:...
. The result of this work was published in 1893.
After receiving his doctorate degree from the University of Giessen
University of Giessen
The University of Giessen is officially called the Justus Liebig University Giessen after its most famous faculty member, Justus von Liebig, the founder of modern agricultural chemistry and inventor of artificial fertiliser.-History:The University of Gießen is among the oldest institutions of...
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
Jena
Jena is a university city in central Germany on the river Saale. It has a population of approx. 103,000 and is the second largest city in the federal state of Thuringia, after Erfurt.-History:Jena was first mentioned in an 1182 document...
, Germany, by Siegfried Czapski
Siegfried Czapski
-Overview:See the German Wikipedia article :de:Siegfried Czapski for details of Siegried Czapski's life.Czapski succeeded Ernst Abbe as the head of Carl Zeiss in Jena in 1903....
based on his earlier work on improving microscope illumination. He stayed with Zeiss as a physicist
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
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
Professor
A professor is a scholarly teacher; the precise meaning of the term varies by country. Literally, professor derives from Latin as a "person who professes" being usually an expert in arts or sciences; a teacher of high rank...
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.
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 gas lamps, mirrors or other primitive light sources, resulting in an uneven specimen illumination unsuited for producing good quality photomicrographs using the slow-speed emulsionEmulsion
An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...
s available at the time. Over the course of his work for his doctorate degree, Köhler developed a microscope configuration that allowed for an evenly illuminated field of view and reduced optical glare from the light source. It involved a collector lens for the lamp that allowed the light source to be focused on the front aperture
Aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...
of the condenser. This in turn allowed the condenser to be focused on the specimen using a field diaphragm
Diaphragm (optics)
In optics, a diaphragm is a thin opaque structure with an opening at its center. The role of the diaphragm is to stop the passage of light, except for the light passing through the aperture...
and condenser focus control. This superior illumination scheme is still widely used in modern microscopes and forms the basis for phase contrast
Phase contrast microscopy
Phase contrast microscopy is an optical microscopy illumination technique of great importance to biologists in which small phase shifts in the light passing through a transparent specimen are converted into amplitude or contrast changes in the image.A phase contrast microscope does not require...
, differential interference contrast
Differential interference contrast microscopy
Differential interference contrast microscopy , also known as Nomarski Interference Contrast or Nomarski microscopy, is an optical microscopy illumination technique used to enhance the contrast in unstained, transparent samples...
, epifluorescence, and confocal microscopy
Confocal microscopy
Confocal microscopy is an optical imaging technique used to increase optical resolution and contrast of a micrograph by using point illumination and a spatial pinhole to eliminate out-of-focus light in specimens that are thicker than the focal plane. It enables the reconstruction of...
.
Köhler's groundbreaking work on microscope illumination was published in the Zeitschrift für wissenschaftliche Mikroskopie in 1893 in Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, followed by an English summary of his work in the Journal of the Royal Microscopical Society one year later. 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
Royal Microscopical Society
The Royal Microscopical Society is an international scientific society for the promotion of microscopy. RMS draws members from all over the world and is dedicated to advancing science, developing careers and supporting wider understanding of science and microscopy through its Science and Society...
in 1994. 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 SchottOtto Schott
Friedrich Otto Schott was a German chemist, glass technologist, and the inventor of borosilicate glass. He was the son of a window glass maker, Simon Schott. From 1870 to 1873 Schott studied chemical technology at the technical college in Aachen and at the universities of Würzburg and Leipzig...
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 ultraviolet light (together with his colleague Moritz von Rohr
Moritz von Rohr
Moritz von Rohr was an optical scientist at Carl Zeiss in Jena.A street in Jena is named after him: Moritz-von-Rohr-Straße, near Carl-Zeiss-Promenade and Otto-Schott-Straße, reminders of the proud optical heritage of the city.-Life:...
), pioneering what would become the starting point for fluorescence microscopy, and the discovery of grid illumination, a method that would later be used in the treatment of tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
s. A suggestion by Köhler led to the development of parfocal
Parfocal
A parfocal lens is a lens that stays in focus when magnification/focal length is changed. There is inevitably some amount of focus error, but small enough to be considered insignificant.-Microscopy:...
lenses which allow the specimen to remain in focus when changing objectives on a microscope.
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 kinematographs, microscope applications, and light and dark field illumination, among others. He filed an application for a fixed-ocular microscope of his design in Germany on April 16, 1924 and with the United States Patent Office on March 31, 1925 (patent number 1649068). 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 diatomDiatom
Diatoms are a major group of algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons , fans , zigzags , or stellate colonies . Diatoms are producers within the food chain...
s.