Joseph Fraunhofer (6.03.1787-7.06.1826) was a German physicist. He was born in Straubing. In 1806 he began work as an optician and mechanic in an optical workshop in Munich, and then in Benediktbeuern (Bavaria), of which he became manager in 1809 and head and owner in 1818. From 1823 he was keeper of the physics cabinet and professor at the University of Munich.
His work was in the field of physical and practical optics. He made a significant contribution to the study of dispersion and to the making of achromatic lenses. He produced sufficiently large and pure specimens of flint glass and crown glass and invented a method of determining the shape of lenses precisely, which had a considerable influence on the development of practical optics; he invented a machine for grinding achromatic lenses and designed a spectrometer, an achromatic microscope, an eyepiece micrometer and a heliometer. Independently of W. Wollaston he observed (1814—15), and was the first to investigate and explain, the dark lines in the solar spectrum, later named after him (Fraunhofer lines); in particular, using the phenomenon of diffraction, he measured their wavelength. He studied diffraction in parallel rays (the so-called Fraunhofer diffraction), first from a single slit and then from many. A great merit of Fraunhofer's is his wide use (from 1821) of diffraction gratings for the study of spectra (some investigators even regard him as the inventor of the first diffraction grating).