The modulation contrast microscope: principles and performance

The modulation contrast microscope produces an image of high contrast and resolution. The image has a three‐dimensional appearance wherein a rounded object appears dark on one side, bright on the other with grey in between against a grey background. The performance features are optical sectioning, directionality, high resolution and control of contrast and coherence. A bright field microscope is converted to the modulation contrast microscope by adding the modulator, a special amplitude filter, in the objective. A slit aperture part of which is polarized is placed before the condenser. Below this is a rotatable polarizer. The modulator processes light from opposite gradients oppositely, that is brighter for one and darker for the other; thereby preserving the sign. The diffraction theory has been extended to show that gradient image intensity is the intensity of the zero order and when modified by the modulator creates a high contrast image.