Frits Zernike developed phase-contrast microscopy, making transparent structures visible through changes in wave phase. A weakly absorbing specimen may change the wave phase of transmitted light without producing much ordinary intensity contrast. Shifting the relative wave phase of the direct and diffracted components lets their wave interference convert that information into visible brightness differences. His discovery began with imperfections in diffraction gratings, before becoming a method for observing transparent specimens.[ref]
How I discovered phase contrast by Frits Zernike. 1953 authored lecture, diffraction-grating motivation and phase-strip microscopy
A physicist.[ref]
https://www.rug.nl/fse/nobelprize-zernike/frits-zernike-1888-1966?lang=en. Independent professional profile
Portrait of Frits Zernike
. Anefo; Nationaal Archief, 4 November 1953. Individual photographer not separately named in the File. Creative Commons CC0 1.0 Universal Public Domain Dedication. Source usage terms, via Wikimedia Commons. Source. Articles by others on the same topic
Frits Zernike was a Dutch physicist known for his significant contributions to the field of optics, particularly in the development of phase contrast microscopy. He was born on July 16, 1888, and passed away on March 10, 1966. Zernike's work enabled the visualization of transparent specimens, such as living cells, without the need for staining, which can alter their natural state.