Phase contrast was not discovered while working with a microscope, but in a different part of optics.
About 1930, our laboratory had obtained a large concave grating and set it up in a Runge-Paschen mounting.
How quick are we to learn: that is, to imitate what others have done or thought before. And how slow to understand: that is, to see the deeper connections.
With the phase-contrast method still in the first somewhat primitive stage, I went in 1932 to the Zeiss Works in Jena to demonstrate. It was not received with such enthusiasm as I had expected.