In this article we will discuss about the parts and working of phase contrast microscope.
1. Phase contrast microscope was discovered by Professor Frits Zernike of Netherlands. Its commercial production was first started in Germany in 1942. For the recognition of his discovery of phase contrast, Zernike was awarded Noble Prize for Physics in 1953.
2. Only living and unstained cells are studied under phase Contrast microscope. It is so because the living cells are not usually coloured (i.e., they are pure phase objects), but the light transmitted by their different structures will have phase differences caused both by variations in refractive index arising from changes in protoplasmic concentration and by difference in thickness.
3. This is a specially designed light microscope in which annular phase plate and annular diaphragm (Fig. 280) are fitted.
4. The annular diaphragm is situated below the condenser. It is made up of a circular disc having a circular annular groove. The light rays are allowed to pass through the annular groove. Through the annular groove of the annular diaphragm, the light rays fall on the specimen or object to be studied. At the back focal plane of the objective develops an image. The annular phase plate is placed at this back focal plane.
This phase plate is either a negative phase plate having a thick circular area or a positive phase plate having a thin circular groove. This thick or thin area in the phase plate is called the conjugate area. The phase plate is a transparent disc.
5. With the help of the annular diaphragm and the phase plate, the phase contrast is obtained in this microscope. This is obtained by separating the direct rays from the diffracted rays. The direct light rays pass through the annular groove whereas the diffracted light rays pass through the region outside the groove.
6. Depending upon the different refractive indices of different cell components, the object to be studied shows different degree of contrast in this microscope.
7. No special preparation of fixation or staining, etc. is needed for study an object under phase contrast microscope. This saves a lot of time of the researcher because a clear picture of unstained or living cells is easily seen under this microscope.
8. Applications of phase contrast microscopy in biological research are numerous.
With this microscope, one can study:
(i) the actual processes of mitosis and meiosis in living cells;
(ii) the actual effects of several chemicals on the living cells;
(iii) the behaviour of several microscopic organisms (e.g., Protozoans) towards various chemical and physical factors and;
(iv) processes related to permeability of plasma membrane, etc.