Light vs Electron Microscope
There are more animals living in the scum on the teeth in a man’s mouth than there are men in a whole kingdom.
Antony van Leeuwenhoek
A microscope is an instrument used to see objects which are not directly visible to naked eyes. The word microscope is derived from the Latin word ‘micro’ (=small) and the Greek word ‘skopos’ (=to look at). The present decade’s development in science and technology produced varied types of microscopes with wide and diverse applications.
Major credits for the current developments in biological sciences goes to the technological advancements in the field of microscopy which allowed scientists to visualize not only minute structural features but also many molecular and physiological pathways within the cells. The significance of microscopy in biological sciences if further evident when we see the history of Nobel Prize. Almost all types of microscope discoveries and their further advancements have been awarded with Nobel Prize.
There are two fundamental types of microscopes; they are optical (light) microscopes which employ glass lenses and visible spectrum of light; and electron microscope which employ electromagnetic lenses and beam of electrons for image formation.
This post is describes the similarities and fundamental differences between these two type of microscopes namely optical (light) microscope and Electron microscope.
Similarities between Light Microscope and Electron Microscope
Ø Both microscopes are used for visualizing small objects which are not directly observable by naked eyes
Ø Specimen preparations such as sectioning, staining mounting etc are required in both types of microscopes prior to observation
Ø Both types of microscopes are used in research applications
Ø Both microscopes follow Abbe’s law
Ø Microphotography is possible with both microscopes
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Differences between Light and Electron Microscope
Sl. No. Light Microscope Electron Microscope 2 Zacharias Janssen in 1590 invented the first prototype of compound microscope Discovered by Ernst Ruska and Max Knoll in 1931 3 Illuminating source is visible light (white light) Illuminating source is accelerated beam of electrons from a tungsten filament 4 Uses optical lenses to bend light beam to form the image of specimen Uses electromagnets (electromagnetic lenses) to bend beam of electron to form the image of specimen 5 Wave length of light used is 450 to 750 nm Wave length of electron beam used is 0.5 Å 6 Illuminating light pass through the air Illuminating beam of electrons pass through the vacuum 7 Vacuum condition is not required for the working of light microscope Vacuum condition is essential for its working since electron beans due to its shot wave length can be easily deflected and retarded by molecules in the air 8 All lenses (condenser, objective and eye piece lenses) are made of glass or quarts Complete lens system are made of electromagnets, no glass lenses are used 9 Specimen is mounted on glass slide Specimen is mounded on metallic grid (usually copper) 10 Focusing is by adjusting the lens position mechanically Focusing is done by adjusting the power of electric current to the electromagnetic lenses 11 Image formation depends upon the differential absorption of light by different regions of the object Image formation depends upon the scattering of electron beams by different regions of the object due to heavy metal staining 12 Magnification is changed by changing the objective or eye piece lenses Magnification is changed by adjusting power of electric current to the electromagnetic lenses 13 Magnification limit is less, possible limit is 1500 X Magnification limit is very high, possible limit is 500000X 14 Limit of resolution is ~ 200 nm Limit of resolution is 0.1 nm 15 Fixed or un-fixed, Stained or unstained, living or nonliving specimens can be observed Only fixed, stained and non-living specimens can be observed 16 The preparatory steps are relatively simple, it may take few minutes to an hour Tedious specimen processing steps are involved prior to observation, it may take few days to complete 17 Image can be observed with naked eye Image cannot be observed with naked eyes, since electron beam cannot be visualized by human eye. For the visualization of images, fluorescent screen or photographic plates are used 18 Colour imparting dyes are used for staining to provide contrast and differentiation Heavy metals are used as stains, which deflect the electron rays to produce the image 19 Natural colour of specimen can be visualized Natural colour of specimen cannot be visualized 20 Live cell imaging is possible and hence the living cellular processes can be visualized Live cell imaging is not possible and hence the living cellular processes cannot be visualized 21 Colour photography is possible Colour photography is not possible. Images are always black and white For colour images, pseudo-colour (false colour) is used 22 Size of instrument is comparatively smaller and can be operated as a desktop instrument Size of instrument much larger, separate systems like cooling system, vacuum system, image processing system etc. are involved. 23 Price is much cheaper when compared to electron microscope Electron microscope is extremely costly instrument
.JPG)
Figure 1: A Light Microscope; Figure 2: An Electron Microscope
An algal cell under Light Microscope
Pollen grains under Electron Microscope
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