All About Laboratory Microscopes

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

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.

Support System

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.

Light System

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.

Lens System

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.

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Some Things You Should Know About Dissecting Microscopes

Dissecting microscopes are used for examining small organisms, fine dissection work and demonstration. You cannot use them to examine biological samples like cells. They are generally used to view larger samples and usually have a magnification power of less than 100x. The parts of this type of microscope include an eyepiece, a tube, a knob for adjusting magnification and focus, an arm, auxiliary lens, a stage plate and the base. The specimen is kept on the stage plate to be viewed.

These are usually used in schools for educational purposes. They can also be found in biological or research laboratories for examination and demonstration purposes.

The Parts

The tube of the microscope has an eyepiece on the top fitted with a lens to look through. There will also be a nose piece to support your nose in order to keep your head steady while using it. There is an objective lens at the bottom part of the tube. You will have to fit an objective lens depending on the type and size of the specimen you wish to view. You have to fit them depending on the sharpness of focus that you will need. You will need to use a finer focus for really small specimens.

There will be two more lenses in the condenser. These are light condensing lenses and are required to adjust the magnification of the microscope. The condenser is placed above the stage of the microscope. The stage is where the slide with the specimen is placed. The stage should be an adjustable one which can be maneuvered without you having to remove your eyes from the eyepiece.

The stage is placed above the diaphragm. The diaphragm controls the amount of light falling on the specimen. The light can either be transmitted from below the stage or above. It could be of many types but the fluorescent type is the best as it emits more light and less heat. You are able to see the magnified image of the specimen due to the manipulation of the light's reflection on the specimen.

Taking Care Of Them

All microscopes need to be handled with care and stored carefully. Dissecting microscopes need to have their lenses cleaned on a daily basis with a soft cloth so that they remain smudge and dust free. You should not allow any dampness to come on them so they should be kept away from water. Whenever you are not using them, you should keep them covered with dust covers. Microscopes need to be kept spotlessly clean. Any speck of dust on the lens can affect their proper functioning.

You must be very careful when picking up and carrying a microscope. It is imperative that you hold it with both hands. This way you can avoid bumping it into things or dropping it. If you drop it, the alignment of the stage and lenses can get ruined. Microscopes can be rather expensive so it is better to take proper care of them so that you can use them for much longer. You can get different accessories for microscopes. The best thing to do is to buy a case in which you can store the microscope and its accessories so that they do not get dirty or damaged.

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