In 1953, Frits Zernike discovered this microscope, which is mainly used to visualize unstained living cells. It is an optical microscopy technique that converts phase shifts in the light passing through a transparent specimen to brightness changes in the image. Phase shifts are invisible, but they become visible based on brightness variations. This microscope allowed biologists to study living cells and their multiplication through cell division.
Principle:
The main principle is based on the small
phase changes in the light rays, induced by differences in the thickness and
refractive index of the different parts of an object, which can be transformed
into differences in light intensity.
In simple terms, it is the translation of invisible phase
shifts into visible differences in intensities (Fig). In a phase-contrast
microscope, image contrast is increased in two ways: by generating constructive
interference between scattered and background light rays in regions of the
field, and by reducing the amount of background light that reaches the image
plane.
Fig: Phase contrast microscope
Components: It has a light source, condenser,
objective lens system, ocular lens system, annular diaphragm, and phase plate.
Applications:
1. It enables the visualization of living and unstained
cells.
2. It is used to visualize various cell organelles like
mitochondria, nuclei, vacuoles, etc.
3. It helps to study cellular events like cell division,
phagocytosis, etc.
4. It helps to visualize cellular movements like chromosomal
and flagellar movements.
5. It is used to observe the growth of the living cells in
the plant tissue culture techniques.
6. It is used to study the membrane permeability of the
cells.
Advantages:
1. It provides clear images of unstained cells.
2. It provides high-contrast images of the cells.
3. It restricts the damage of the cells due to chemical
preparation and staining.
4. It enhances the prolonged observation of living cells.
5. Its cost is affordable.
6. It is widely applied in biological and medical research,
especially throughout the fields of cytology and histology.
Disadvantages:
1. It produces a bright holo surrounding the image because
of the partial formation of direct and deviated rays.
2. It is only effective to observe individual cells.