Phase contrast microscopy utilize an optical mechanism to translate minute variations in phase into corresponding changes in amplitude, which can be visualized as differences in image contrast.
Most of the detail of living cells is undetectable in bright field microscopy because there is too little contrast between structures with similar transparency and there is insufficient natural pigmentation. However the various organelles show wide variation in refractive index, that is, the tendency of the materials to bend light, providing an opportunity for phase contrast microscope to distinguish them. A phase contrast microscope does not require to kill the cells by staining. This made it possible to study live cells.
The differences between the photos of the decaying algae are especially dramatic. The internal chlorophyll and other internal organelles are very much lose due to the lack of energy (I have left it in a bottle away from the window). The border of the cell wall is barely visible under the bright field while image observed in phase contrast has very clear borders. The details of the amoeba is still clearly visible due to the colors of the vacuoles. The phase contrast photo lose the color. However, the phase change allow it to show the 3D effect of the organism – I would describe that as the moon surface.
The picture was taken with a Tucsen 3.0 MP CMOS microscope camera from Nexcope CM501 with phase contrast kit.
Note: The phase contrast kit also include the dark field option. Below is the picture of a rotifer and diatoms using the dark field option.