Ernst Abbe (1840-1905), professor of physics and mathematics at the University of Jena, Germany, and major partner in the Carl Zeiss company, made important contributions to the theory and practice of optical microscopy. His compound microscope is a superb optical design based on a theoretical understanding of diffraction and the minimization of the effects of aberrations. Abbe enunciated his famous sine condition with regard to the axial point in the object plane of a centered image-forming system, such as a microscope or a telescope. When this condition is satisfied, "aberration-free" imaging of the object points located in the vicinity of the optical axis is assured.
by Masud Mansuripur