Its inventor Frits Zernike was studying since 1930 at the University of Groningen the modifications of spectral lines by diffraction gratings. He observed that the image errors in the concave networks are due to a phase shift of the diffracted rays.
Zernike had the idea of visually revealing that loss of coherence by producing an interference with a reference beam. He published in 1933 in a congress its application to microscopy. Nobody was convinced.
During the war Nazi scientists endeavored to exploit all inventions that could bring them some technological advance. They finally understood the practical interest of the concept proposed by the Dutch physicist. Commissioned by the German power, the Zeiss company manufactured from 1941 this phase contrast microscope which will become after the war an indispensable instrument for the microbiologists all over the world.
The Nobel Prize in Physics is awarded to Zernike in 1953. His medal is estimated $ 100K for sale by Bonhams in New York on December 6, lot 98.