[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.

[1] 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.

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.

[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.

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.

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,[8] and the discovery of grid illumination, a method that would later be used in the treatment of tumors.

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.