Ernst Karl Abbe (January 23, 1840 – January 14, 1905) was a German physicist and professor at the University of Jena. He was born in Eisenach, Saxe-Weimar-Eisenach, and died in Jena. Abbe is best known for his work in optics.

Life Work

He designed the first refractometer, which he described in a booklet published in 1874.He created the Abbe number, a measure of any transparen material's variation of refractive index with wavelength. Already a professor in Jena, he was hired by Carl Zeiss to improve the manufacturing process of optical instruments, which back then was largely based on trial and error. In a long and fruitful collaboration, Abbe created the mathematical foundation of microscope design, which became essential for the later preeminent position of the Zeiss company. In particular, he discovered the Abbe sine condition, a breakthrough in lens design. He also invented the Abbe condenser, used for microscope illumination.During his association with Carl Zeiss' microscope works, he also introduced the eight-hour workday, in remembrance of the 14-hour workday of his own father.

The crater Abbe on the Moon was named in his honour.

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