On January 23, 1840, German physicist, optometrist, entrepreneur, and social reformer Ernst Abbe was born. Together with Otto Schott and Carl Zeiss, he laid the foundation of modern optics. As a co-owner of Carl Zeiss AG, a German manufacturer of research microscopes, astronomical telescopes, planetariums and other optical systems, Abbe developed numerous optical instruments.
Abbe was born in Eisenach in 1840 and was lucky to be financially supported by his father’s boss, who guaranteed him a modest education. The young Abbe was talented in nature sciences wherefore he was able to attend the University of Jena and the University of Göttingen. After studying, he was occupied at the observatory in Göttingen and later began his career in physics at Frankfurt and Jena. Abbe was awarded his PhD in Göttingen in 1861. In 1863, Abbe qualified as a university lecturer at the University of Jena. He became director of the observatory of Jena and a member of the ‘Academy of Sciences’.
In 1866, Carl Zeiss, back then the university’s mechanic, invited Abbe to help him constructing a scientific microscope and after some difficulties at the beginning, both engineers were able to critically improve the microscopes with their invention of the apochromatic lens, a microscope lens which eliminates both the primary and secondary color distortion. From then on, Ernst Abbe began his career as Zeiss’ partner. By 1870, Abbe invented the Abbe condenser, used for microscope illumination. In 1871, he designed the first refractometer,a laboratory or field device for the measurement of an index of refraction (refractometry). He developed the laws of image of non-luminous objects by 1872. Zeiss Optical Works began selling his improved microscopes in 1872, by 1877 they were selling microscopes with homogenous immersion objective, and in 1886 his apochromatic objective microscopes were being sold.
He created the Abbe number, a measure of any transparent material’s variation of refractive index with wavelength and Abbe’s criterion, which tests the hypothesis, that a systematic trend exists in a set of observations (in terms of resolving power this criterion stipulates that an angular separation cannot be less than the ratio of the wavelength to the aperture diameter, see angular resolution). However, next to the partnership with Carl Zeiss, Ernst Abbe also became famous for his publications in thermodynamics, mechanics and various theories on optics. Abbe constructed the very first refractometer, he was responsible for developing the ‘Abbe number’ and defining the term ‘numerical aperture’ as well as for the discovery of microscope’s resolution limits. In order to produce high quality objectives, Abbe made significant contributions to the diagnosis and correction of optical aberrations, both spherical aberration and coma aberration. He also perfected the interference method by Fizeau, in 1884
Abbe’s work with Carl Zeiss not only made him famous, but also wealthy. After Zeiss’s death, Abbe founded the Carl Zeiss Foundation and became highly active in concerns of social and political issues. He supported the social democrats, introduced the 8 hour working day, in remembrance of the 14-hour workday of his own father, and supported the freedom of assembly. In addition, he created a pension fund and a discharge compensation fund. Abbe depicted one of the founders of a newspaper, attempting to distribute politically independent news, wherefore he was loved by his employees as well as the general public of Jena. In 1889, Ernst Abbe set up and endowed the Carl Zeiss Foundation for research in science. The aim of the foundation was “to secure the economic, scientific, and technological future and in this way to improve the job security of their employees.” He made it a point that the success of an employee was based solely on their ability and performance, not on their origin, religion, or political views. In 1896, he reorganized the Zeiss optical works into a cooperative with profit-sharing.
Ernst Abbe was appreciated as a brilliant engineer and a courageous social and political reformer in Germany. He was honored numerous times through monuments, the lunar crater ‘Abbe’ was named after him and the Ernst Abbe Foundation was developed. Ernst Abbe passed away on January 14, 1905 in Jena.
References and Further Reading: Ernst Abbe Biography at MacTutor History of Mathematics Archive
 Ernst Abbe at Zeiss
 Ernst Abbe at Britannica Online
 Meister der Mikroskope by Kay Müllges [In German]  Hippolyte Fizeau and the Speed of Light, SciHi Blog, September 23, 2014.
 Ernst Abbe at Wikidata
 Ernst Abbe Timeline at Wikidata