Question: Who developed Phase Contrast?
About the article "Microscope", section "Rise of modern light microscopy".

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  --- microscopy, phase-contrast  
  --- microscopy, phase-contrast  
  "In electron microscopy: Phase-contrast imaging" Phase contrast.
More sophisticated techniques will show proportional differences in optical density.
Phase contrast is a widely used technique that shows differences in refractive index as difference in contrast.
It was developed by the Dutch physicist Frits Zernike in the 1930s (for which he was awarded the Nobel Prize in 1953).
The nucleus in a cell for example will show up darkly against the surrounding cytoplasm.
Contrast is excellent; however it is not for use with thick objects.
Frequently, a halo is formed even around small objects, which obscures detail.
The system consists of a circular annulus in the condenser, which produces a cone of light.
This cone is superimposed on a similar sized ring within the phase-objective.
Every objective has a different size ring, so for every objective another condenser setting has to be chosen.
The ring in the objective has special optical properties: it, first of all, reduces the direct light in intensity, but more importantly, it creates an artificial phase difference of about a quarter wavelength.
As the physical properties of this direct light have changed, interference with the diffracted light occurs, resulting in the phase contrast image.
One disadvantage of phase-contrast microscopy is halo formation (halo-light ring). 
Quadrature modulates two signals by changing the in-phase and quadrature phase components, corresponding to Cartesian coordinates.
By contrast, one can instead consider this to be changing the amplitude and phase of a wave, which corresponds to polar coordinates.
The corresponding modulation is called polar modulation, and was developed earlier, in the 1874 quadruplex telegraph by Thomas Edison. 
[[File:S cerevisiae under DIC microscopy.jpg|thumb|left|150px[[File:Phase shift image of cells in 3D.jpg|thumb|rightThe height and color of an image point correspond to the optical thickness,which only depends on the object's thickness and the relative refractive index.
The volume of an object can thus be determined when the difference in refractive index betweenthe object and the surrounding media is known.
]]The success of the phase contrast microscope has led to a number of subsequent phase imaging methods.
In 1952 Georges Nomarski patented what is today known asdifferential interference contrast (DIC) microscopy.
It enhances contrast by creating artificial shadows,as if the object is illuminated from the side.
But, to achieve this DIC microscopy uses polarized light,making it unsuitable when the object or its container alter polarization.
With the growing use of polarizing plastic containers in cell biology,DIC microscopy is increasingly replaced byhoffman modulation contrast microscopy,invented by Robert Hoffman in 1975.
Traditional phase contrast methods enhance contrast optically, blending brightness and phase information in single image.
Since the introduction of the digital camera in the mid-1990s, several new digital phase imagingmethods have been developed, collectively known as quantitative phase contrast microscopy.
These methods digitally create two separate images, an ordinary bright-field imageand a so-called "phase shift image".
In each image point, the phase shift image displays the "quantified" phase shift induced by the object,which is proportional to the optical thickness of the object.