Ernst Abbe

Ernst Abbe (1840 to 1905) was a German physicist, optical engineer, businessman and social reformer, born in Eisenach to a spinnery foreman. After studying at Jena and Gottingen and taking his doctorate at Gottingen in 1861, he qualified as a university lecturer at the University of Jena in 1863 and in 1866 became research director at the Zeiss Optical Works. In 1868 he invented the apochromatic microscope lens, by 1870 the Abbe condenser, and in 1871 he designed the first refractometer. He defined numerical aperture, showed that the aperture sets the upper limit of microscope resolution, and created the Abbe number, a measure of how the refractive index of a transparent material varies with wavelength. With Carl Zeiss and Otto Schott he helped form the Jena glassworks in 1884, and he became a co-owner of Carl Zeiss.