Different Types of Microscopes

The history of microscope can be traced back to the sixteenth century, when the crude form of this instrument was invented. This instrument got more and more sophisticated with the advent in science and technology and is now available in various types, which are used for different purposes. The most common among them is the oldest and simplest type of microscope, called optical or light microscope, which has three types - simple, compound light and stereo. The others include electron microscopes, which are available as transmission electron microscope (TEM), scanning electron microscope (SEM), reflection electron microscope (REM) and scanning transmission electron microscope (STEM). The different types of microscopes also include scanning acoustic microscopes, which make use of sound waves to detect and measure variations in acoustic impedance.

What are Microscopes?
Microscopes are instruments which enable the human beings to see those substances and organisms, which cannot be seen with the naked eye. The basic model of a microscope contains one or more lenses, which facilitates the enlargement of images kept in the focal plane of the lens. There are many advanced models of microscopes, which are used for various purposes. Even though, there are different types of microscopes, the three basic types are light (optical), electron and scanning probe microscopes. The different types of microscopes have a common aim, i.e, enlargement of images. The only difference between them is that the method of illuminating the objects vary as per the type. The following are some of the different types of microscopes.

Optical Microscopes
As mentioned earlier, this is the oldest and simplest form of microscope, which is otherwise known as light microscope. These microscopes use visible light and a combination of lenses to enlarge the images of the samples. Two basic types of optical microscopes are simple and compound microscopes. The former bears a single lens, whereas the latter uses a combination of lenses. The stereo or dissecting microscope brings about a three-dimensional image of the sample. The latest type of optical microscope, called digital microscope, also uses light to illuminate the samples. But, these devices are attached with a CCD camera, which facilitates viewing the magnified images in a monitor.

Electron Microscopes
An electron microscope uses a beam of highly energetic electrons to illuminate the object. As compared to the optical microscopes, electron microscopes can produce highly magnified images. Electrostatic and electromagnetic lenses are used in electron microscopes. These lenses control the electron stream and focus it to a specific plane of the sample. This method is similar to that of an optical microscope, which uses light to focus on the specimen. The original version of electron microscope, called transmission electron microscope, makes use of high voltage electron beam for the formation of image. Some parts of the sample may allow the beam to pass through it, while others scatter the beam. This information about the specimen is carried by the beam, which emerges from the sample, which in turn is magnified by the lens system. Sometimes, a monitor is also attached to these microscopes.

Another type of electron microscope, called scanning electron microscope, does not allows the electron beam to pass through the specimen, but, the electron beam scans the surface of the sample and measures the reflection. Scanning tunneling microscopes are very powerful and help in viewing specimens at the atomic level. A scanning transmission electron microscope is used to examine a sample, which has been thinned, in order to enable the microscope to detect the scattering of electrons through the specimen.

Apart from the microscopes discussed above, there are many specialized ones, which are used for particular purposes. A microscope is deemed fit for a particular task, based on its illumination method, type of image it produces, magnification, depth of field, resolution, etc. However, these different types of microscopes have made significant impact in various fields of science and technology, especially, medical sciences.