Microorganisms, as the name denotes, are tiny organisms, which cannot be viewed by the naked eye. You require a microscope to view these structures. Anton Van Leeuwenhoek, in 1674, used a simple single lens microscope to study these organisms. However, later with the invention of the compound microscope, the life of the microorganisms was better understood. There are two basic types of laboratory microscopes- light and electron microscopes.
Light or optical microscopes use light waves to produce the illumination, while electron microscopes use electrons. Light microscopes are used for general laboratory work while electron microscopes are used to study extremely small objects like viruses. Light microscopes can be of different types - bright field, dark field, phase contrast, or fluorescence. The types of electron microscopes are either transmission or scanning microscopes. Bright field microscope is the most widely used microscope in laboratory work.
The microscope consists of a support system, light system, lens system and a focusing system. The systems work together to produce a magnified image of the specimen under examination.
This consists of a base, arm, and a stage. The base and arm are structural parts of the microscope and holds the device in place. The stage of the device holds the slide of the specimen. The slide is positioned and clipped with two metal clips in place and moved by the fingers or fixed by a mechanical stage and is controlled by two knobs.
This system passes the light through the specimen using the light source, the condenser, and the iris diaphragm. An incandescent bulb is used as a light source in bright field microscope. The light passes through the condenser and it focuses on the specimen to be viewed. An iris diaphragm controls the intensity, brightness of the light that passes through the sample. This allows for better viewing by the technician, as he can adjust the intensity of the light as per his need for viewing contrast.
This forms the actual image when viewed through the microscope. The compound microscope has two lenses- an objective lens near the specimen and an ocular lens at the top, which magnifies the image of the specimen. The ocular lens magnifies the image to about 10X. The typical microscope has at least three objective lenses mounted on a rotating nose piece to provide different magnifications. The low power objective lens magnifies image to 10X, middle-sized lens is high dry objective lens, which magnifies it between 40X and 45X and the longest lens is the oil immersion lens, which enlarges between 97X and 100X. You would use a high power objective lens to magnify smaller images and low power lenses to magnify large specimens.
There is limitation with the amount of magnification you can produce with a light microscope. The resolving power of the lens is the highest magnification, which can be achieved by producing an image of good resolution. The resolving power is the shortest distance between two closely adjacent points, which can be seen and is based on the nature of the lens used as well as the wavelength of the light source. The maximum resolving power with a light microscope is about 0.2 micrometers.
If you are planning to buy a laboratory microscope, there are several manufacturers now available in the market. You need to know how to spot a good one and choose the one, which will provide the highest quality of viewing.
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