Alexander Lvovich Gershun (29.10.1868-8.06.1915) was a Russian physicist. He was born in the town of Sokolka, Grodno Province (now in the Polish People's Republic). He graduated from St Petersburg University (1890), where in 1890—1902 he was an assistant and a laboratory assistant in the department of physics. In 1902—08 he was head of the department of general physics of the Artillery Officers' Class in Kronstadt, in 1908—12 head of the optical section of the Obukhov works in St Petersburg (and at the same time, from 1908, head of the department of physics of the St Petersburg Women's Pedagogical Institute), and from 1912 scientific director of the Russian Society for Optical and Mechanical Production.
His main research concerned applied optics. He organised the optical industry in Russia and created a number of optical instruments for the navy, in particular new designs of range finders and sights. His work was also in the fields of geometrical and physical optics, electromagnetism and radioactivity.