Henry Friedrich Wilhelm Siedentopf (22.09.1872-8.05.1940) was a German physicist. He was born in Bremen. In 1896 he received the degree of Doctor of Philosophy at the University of Göttingen. From 1899 he worked at the Zeiss optical works (in 1907 —38 as head of the microscopy laboratory), and from 1918 he was also professor at the University of Jena.
His scientific research was devoted mainly to microscopy. Together with R. Zsigmondy he invented (1903) the slit ultramicroscope. He constructed the capillary microscope. He was one of the pioneers of ultramicroscopy and photomicrography.