Types of Microscopes

The evolution of microscopes unlocked a world previously unseen by the naked eye. It ushered in the new field of microbiology and allowed us to study the minute facets of hidden life that exists cloaked with the limitations of our field of vision. A microscope is basically a tool which uses a medium to detect surface reflection and allow it to be visualized by humans.

Light or Optical Microscopes

Light microscope

A Light microscope

The earliest type of microscope uses light waves as the medium and our own human eyes as the receiver. Lenses amplified the amount of light reaching our eyes, as they reflect and pass through on the subject. Cells, prokaryotes, and plankton were all visualized using this type of microscope. The magnification attained was based on the lenses used and the resolution limited only by the inherent limitations of light as a medium. Magnification initially started from 10 times but can now be made to attain up to 1500x useful magnification. The resolution limit of today’s light microscopes is usually 0.2 micrometers. The outer features of cells as well as their interior can now be visualized and studied due to the optical microscope. Use of ultraviolet radiation can extend this limit somewhat at the cost of clarity.  The specimen can be viewed by peering into the eyepiece; the image can be adjusted using fine and coarse adjustment knobs; and the magnification and resolution can be changed by adjusting the revolving nosepiece.

Different types of microscope are used to study different aspects of the cell. A phase contrast optical microscope is used to study a single specimen over time, elucidating the process of the cell cycle.  The advent of technology now allows a CCD  or charged-coupled device to replace the eye as the direct receiver of light, allowing computer displays to directly output the microscopes view.

Electron Microscopes

Siemens-electron-microscope

Siemens electron microscope

During the 1960s, a new medium was tapped to exceed the magnification offered by light. The electron microscope by Ernst Ruska and Max Knoll created during the early 1930s took microscopy to a whole new level. The electron, a subatomic particle, was used to obtain magnification a thousand times more than what the naked eye can see. Instead of a light source, cathode ray tubes were used to generate streams of electrons while instead of the eye, a computer was utilized to detect the reflected electron particles and to generate a visual image. Electromagnetic lenses serve to focus the beams until they hit the sample. This allowed scientists to see the outer surface of the object (scanning electron microscope) as well as to use it in a way similar to optical microscopes (transmission electron microscope). The scanning electron microscope uses electron beams to view the outer surface, distinguishing features based on comparative elevation. The transmission electron microscope follows the same principle as the light microscope, with electrons passing through the subject used to generate images. This is called electron diffraction. Electron microscopes, due to their shorter wavelengths (100,000 times shorter than light’s) allow greater magnification (10,000,000x) and higher resolution (50 picometers). 

Acoustic microscopes

The acoustic microscope, uses sound waves as the medium. Similar to sonar, the acoustic microscope uses sound waves to “bounce” from a structure, and a computer to detect the differences in the rate of return of the waves. It allows for a comprehensive surface view of the structure being observed.

The advent of microscopes helped scientists discover a whole new, microscopic world. This has led to a revolution in various fields, from biology, to medicine to forensics. With these tools, the inner working of the smallest unit of life can now be viewed. The different types of microscopy allow us to have the tools necessary for every specific need. And with the continuous technological innovation we have, the field of microscopy remains promising.

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