Study of different types of microscopes
1) Compound optical or light microscope
- Light microscope uses visible light (wavelength = 390 – 760nm) and achromatic glass lenses to obtain high resolving power and magnification for studying detailed structure of small objects.Resolve all Your Biology Doubts from Physics Wallah.
- Two types of components together constitute a compound microscope – optical and non optical.
- Non optical parts are base, pillar, inclination joint, arm, body tube, a draw tube, coarse and fine adjustments, rack and pinion, automatic stop, stage with central hole, stage clips and resolving nose piece.
- Optical components are objective lenses (3 or 4 with 10x, 45x, 100x magnification), Ocular lens (of 5x to 15x magnification), Reflector (a plano-concave adjustable mirror), condenser to condense the light received from reflector, diaphragm to regulate the amount of light required.
- One of the objective lenses is oil immersion lens and this oil immersion is used only in case of permanent slide.
- The oil used is paraffin oil or cedar wood oil to give higher magnification and resolution along with sharpness of image.
Fig 1. Path of light in a compound microscope
- It cannot be used to study thick objects.
- It cannot be used to study detailed structure of living objects.
- Resolving power is limited (i.e., 0.25mm), while many cellular components are smaller.
2) Dark field microscope / Ultramicroscope
- It was developed by Zsigmondy in 1905.
- It is used for achieving a marked contrast between living organisms and the dark background.
- The sample can be viewed only with oblique rays, one can see only those light rays that are scattered from objects. Thus object appears bright but the background remains dark.
- It is useful in observing small living objects and small organelles of living cells.
- Its resolving power is not high.
- It does not give finer details which are available with fixed and stained specimens.
3) Phase Contrast Microscope
- It was developed by Zernicke (1935).
- It has an annular diaphragm and phase plate.
- It is useful in study of living cells and their internal happening like spindle formation, karyokinesis, cytokinesis, pinocytosis etc. as it enhances the contrast between cells and their environments and between internal organelles and their surroundings.
4) Interference Microscope
- It was invented by Lebedoff while improved by Merten et al.
- It is an improvement over phase contrast microscopes as it has a highly accurate optical balance.
- Here, light is split into two beams, one passing through the object and the other along the object.
- It has wider applications, it is used to study living unstained cells, it is relatively easy to vary contrast and to obtain colour effects.
5) Polarizing Microscope
- It has two rotable polarizing devices called polarizer and analyzer.
- It is useful mainly in viewing highly ordered objects which show birefringence such as crystals or bundles of parallel filaments.
- The mitotic spindle, made up of microtubules cannot be resolved by light microscopes, but can be studied with polarizing microscopes.
6) Ultraviolet Microscope
- It was developed by Caspersson (1938)
- It employs U.V rays (1500Å – 3500Å), quartz – fluorite or lithium fluoride lenses and photographic plate for observation.
- It is useful in the qualitative and in some cases quantitative determination of nucleoproteins.
7) Fluorescence Microscope
- Coons (1945) developed fluorescence microsopy.
- Fluorescence microscope used U.V. light with higher wavelength (3500 - 4000Å), stimulation on cell components stained with fluorescent dyes (viz green fluorescein and red rhodamine).
- It is used to detect specific proteins of other molecules in cells and tissues, viz antibodies.