Frederik Zernike (Amsterdam, July 16, 1888 – March 10, 1966) was a Dutch physicist and winner of the Nobel prize for physics in 1953 for his invention of the phase contrast microscope, an instrument that permits the study of internal cell structure without the need to stain and thus kill the cells.
Zernike was the son of Carl Frederick August Zernike and Antje Dieperink, both of whom were teachers of mathematics; Zernike shared his passion for physics with his father. He studied chemistry (his major), mathematics and physics at the University of Amsterdam. In 1913 he became assistant to Jacobus Cornelius Kapteyn at the astronomical laboratory of Groningen University. In 1915, he obtained a position in theoretical physics at the same university and in 1920 he was promoted to full professor of theoretical physics. In 1930, he was conducting research into spectral lines and discovered that the so-called ghost lines that occur to the left and right of each primary line in spectra created by means of a diffraction grating, have their phase shifted from that of the primary line by 90 degrees. This discovery lay at the base of the first phase contrast microscope, built during World War II.