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.

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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Dissecting Microscopes

Most of us remember using microscopes when we were in biology class, watching microscopic organisms moving around, bumping into each other. Although we thrilled to watch the action under the lens, we really didn't pay much attention to the microscope itself. If you were to purchase a microscope today you might be surprised to learn that there are several different types of microscopes available depending on your use.

The most common microscope is the compound microscope which is meant for measuring at higher magnifications from 40X up to 100X. The other type of commonly used microscope is called a stereo or dissecting microscope. It uses two eyepieces and two paired objectives. It may use a built in light source from above, below, or none at all. Magnification is usually from 10X to 40X.

Stereoscopic dissecting microscopes have separate optical pathways for each eyepiece. When viewing your sample you get a three -dimensional view of your specimens at relatively low magnifications. These microscopes also have a large field and a longer working distance than what you find on compound microscopes. Whereas compound microscopes are used for looking at slides, dissecting microscopes are meant for viewing larger samples.

There are two basic types of dissecting microscopes. One style allows you to read at two fixed magnification settings, such as 10X and 20X or 10X and 40X. The other style has the capability to magnify at many settings, or "zoom" rather than to be set at two stationary magnification points. By turning a dial you can literally look at every magnification between two end points, usually 7X and 45X. This greatly increases your ability to view samples.

Dissecting microscopes can be purchased with out without built-in lighting. Built-in lighting involves an upper illuminator for reflected light (episcopic) and a lower illuminator for transmitted (diascopic) light. The most common lighting is by halogen lamps, but you will find a lower fluorescent lamp in some models. Fluorescent illumination is used for examining heat-sensitive specimens such as in embryo transplant work. Accessory light can also be added to dissecting microscopes in the form of a ring light, coaxial illuminator or fiber optic light pipes. Various color filters can be added for specific applications.

You can also vary the stand that your dissecting microscope body sits in, thus changing the working distance. A typical dissecting microscope has a fixed stand with a rack & pinion for moving the body up and down. This gives you a smaller working distance in which to work. You can also purchase your dissecting scope on a boom stand, which greatly increases the space under the scope. This also allows you to have the microscope stand out of the way when you are working with larger items which may normally interfere with the position of the stand.

Although dissecting microscopes always have at a minimum two eyepieces, you can add a third "eyepiece" or port for a camera system. There is a wide array of camera systems available, running from digital to video. Most cameras can be attached to this trinocular port with an adapter, and then linked through a USB port to the software in your computer.

Whether you are a biologist performing dissections, a technician building or repairing circuit boards, a paleontologist cleaning and examining fossils or a hobbyist who needs to work with your hands on small objects such as rocks & bugs, you will find a dissecting microscope to be a very useful tool.

National Microscope Exchange has been in business since 1991, selling and servicing abbe refractometers, refractometers, dissecting microscope and microscopes. The service staff has 30 years of experience with microscopes, and is the authorized United States service facility for Atago brand refractometers, dissecting microscope.

Educational Microscopes

Educational microscopes play a valuable role in today's education and research. As a great education tool, these microscopes help the students to view magnified images of everything from plant cell walls to butterfly wings. Educational microscopes offer maximum flexibility and accuracy for viewing images.

As there are different types of educational microscopes, the one chosen must best suit the student's requirement. A low-power microscope - also called stereo or dissecting microscope - is used to view larger things like stamps, coins, and sand grains. Mostly, it is supplied with 10X and 20X eye pieces. As it is easy to focus, this type of microscope is especially suited for younger children. There are three models to choose from - single power, two power, and zoom type stereo microscope.

High-power microscopes can be used to view minute objects like bacteria, plant cell, and blood samples. Their typical magnification is 40X, 100X, and 400X. High-power microscopes include biological microscopes, compound microscopes, and metallurgical microscopes. Educational compound microscopes are used for viewing the microscopic world. Their magnification can range up to 1000X. Travel Lab, MicroQuest, Explorer II, Observer III, and Observer IV Binocular Microscope are some popular models.

Digital microscopes are also greatly used for education purposes. These microscopes will help the students to view large images on a computer monitor, through a USB connection. Thus, they allow the projection of a microscopic image to a large audience. Moreover, digital microscopes help the students to save and print the images.

Educational microscopes are equipped with triple or quadruple nosepiece, coaxial coarse for accurate focusing, and reflecting mirror. A condenser with magnification indication is also offered. To get optimum resolution, the diaphragm of the condenser is provided with position guide markings for different objectives. Additional features such as illuminator and stopper for slide safety are also available.

Most educational microscopes are cordless and rechargeable. Some models are provided with a digital camera. Software for image capturing is also included. Apart from these, some microscope companies offer additional accessories such as dust cover, immersion oil, and prepared glass slides.

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Inverted Microscopes

Most microscopes that you see in a typical laboratory environment are compound microscopes. They are designed with objectives on a rotating nose piece mounted above the stage, and the light source and condenser below the stage. They are most commonly used for viewing samples that have been fixed to a flat slide.

In certain applications it is necessary to look at live, unfixed samples. A more practical microscope design to use is the inverted microscope. An inverted microscope is a microscope with its light source and condenser on the top, above the stage pointing down, while the objectives and turret are below the stage pointing up. Inverted microscopes are useful for observing living cells, tissues or organisms at the bottom of a large container (such as a tissue culture flask). This allows you to examine the specimen under more natural conditions than on a glass slide, as is the case with a conventional compound microscope. You can place a Petri dish or other container on the stage and view the samples from below, thus not disturbing their more "natural" states. Larger, covered samples are less susceptible to evaporation and increases in temperature, thus preserving suitable living conditions for the specimen you are viewing.

Because of the fact that you have to look through thicker containers you often find the objectives to be long working distance or ultra-long working distance. These objectives have been corrected for observing samples that are further away than what you normally see on a compound microscope. The image may not be quite as clear as when you are looking at a perfectly flat slide. You may want to use a plastic Petri dish rather than a glass one as the plastic dishes are thinner and more uniform. Most inverted microscopes will have objectives that range from 4-40X, with 60X being an added option. You do not usually find inverted microscopes that incorporate 100X objectives.

Inverted microscopes can be configured for work in electrophysiology, in vitro fertilization, micromanipulation, high-resolution DIC, video-enhanced observations, and a variety of advanced fluorescence techniques. Motorized accessories can include shutters, filter wheels, revolving nosepieces, fluorescence block turrets, focus drives, and condensers. Inverted microscopes also allow you to add advanced objectives for water immersion, ultraviolet excitation, and phase contrast. Prices for inverted scopes vary according to the number and types of accessories you add to them, just as in compound microscopes.

The fundamental advantage of an inverted microscope is that it allows you to accept a container with a large and relatively long-lived diverse culture of live organisms without any preparation. This can be invaluable to work which requires the sample to be alive and in as natural an environment as possible.

National Microscope Exchange has been in business since 1991, selling and servicing refractometers, microscopes and inverted microscope. The service staff has 30 years of experience with microscopes, and is the authorized United States service facility for Atago brand refractometers, inverted microscope