physicist whose theoretical and technical innovations in optical theory led to great improvements in microscope design (such as the use of a condenser to provide strong, even illumination, introduced in 1870) and clearer understanding of magnification limits. In 1873 he discovered the optical formula now called the Abbe sine condition, one of the requirements that a lens must satisfy if it is to form a sharp image, free from the blurring or distortion caused by coma and spherical aberration. As head of the Zeiss