The bright field microscope is the most common type of light microscope used for magnification and observation of specimens. This is the simplest and earliest type of microscopy that is used in a variety of settings, including classrooms, clinics, hospitals and research facilities. It uses a source of bright light for examination, where a specimen can either be stained or unstained. Inexpensive models of bright field microscopes typically use a sub stage mirror to provide illumination while other models use a light source that is built into the unit.

Common components of the bright field microscope

The bright field microscope is made up of several parts. They are:

The base – the structure that supports the unit and contains the control for the adjustment of light intensity, which is usually an illuminator or electrical source of light.

Arm – the structure that provides support for the base and the lens system.

Objective lenses – these lenses are located nearest the object or specimen and enlarge the image using a combination of different magnification powers. The objective lens provides the aerial or primary image of the specimen.

Oculars – these are the lenses that magnify an image. These lenses are located nearest to the viewer. The ocular lens magnifies the image to put the primary image in focus. This helps provide the virtual or final image, which is the product of the ocular and objective lenses.

Revolving nosepiece – allows rotation of the objective lenses for better viewing position.

Stage – the platform where the microscope slide is laid and viewed.

Adjustment knobs – consist of the coarse adjustment and the fine adjustment knobs. The coarse adjustment focuses the image using the 4X and 10X objective lenses. The fine adjustment lenses focus the image using the high dry and oil immersion objective lenses (40X and 100X).

Condenser – this may be raised or lowered to focus the light for better viewing of the specimen.

Uses of the bright field microscope

Bright field microscopes provide images that appear dark-colored against a bright field. They are used extensively in classroom settings for the examination of specimen in biology and chemistry. This type of microscope may be used for either stained or unstained specimens. In microbiology, for example, simple stains such as crystal violet and methylene blue as well as differential stains such as flagellar stains, negative stains and endospore stains are often used to enhance details in a specimen for observation. Images of microorganisms may be magnified to a maximum of 400X. When specimens are stained, they can be further magnified with an oil immersion lens to a maximum of 1200X. Bright field microscopes are also effective in bacteriological microscopy because the oil immersion lens allows for increase in resolving power.

Advantages of bright field microscopes

Bright field microscopes are not only easy to use, their setup is also simple, requiring only the most basic equipment. They also allow easy viewing and observation of live cells because there usually is no need to prepare the sample. For images that require viewing enhancements, a bright field microscope may be adjusted manually, allowing manipulation of the light source through the condenser, effectively reducing the resolution. Polarising filters may also be used with the light source to help enhance specimen features that are not apparent when under a white light. This makes bright field microscopes also excellent viewing and magnification tools for mineral samples. They also perform excellently for magnification of transparent, opaque or semi-transparent specimens.

Limitations of bright field microscopes

The bright field microscope is advantageous for images that are either dark or those which have significant refraction because the white background can effectively enhance the image. For other images, a bright field microscope may not provide the best view. The resolution of diffraction is limited to about 0.2 micrometer. Lights that are out of focus located in the external area of the focal plane further reduce the clarity of the image. Some images also do not have the natural contrast that allows them to be studied and viewed successfully using the bright field microscope. Some live specimens may also prove difficult to view using a bright field microscope, limiting imaging in real time.

This is why some specimens have to be stained in order to provide or increase the contrast of the different structural details. Be that as it may, staining may also introduce certain details into the specimen that are not part of the specimen itself, but are instead a caused by the processing. The apparent details may be misconstrued as a feature when in truth, they are not. However, background illumination may be corrected when using the device.

Students of the life sciences begin their studies by learning how a bright field microscope works. Bright field microscopy uses the power of natural light in order to see an object: light passes through the sample, through a system of lenses, and then into an observer’s eyes, giving the microscope user a large view of a largely unseen world. All the parts of a bright field microscope contribute to making the microscope work to serve the basic needs of life scientists everywhere.

Bright field microscopes can be used in many fields. Biologists use it to identify organisms, look at cellular components, and even estimate how many microorganisms are present in a sample. Medical technologists use it to identify infectious microbes, and their results can be used by doctors in order to make a diagnosis of their patients. Laboratories use bright field microscopes not only to conduct research, but to teach students the basics of microscopy as well.

What are the Components of Most Bright Field Microscopes?

Bright field microscopy is a general term that covers different microscopes that all employ visible light to show a specimen. A simple microscope uses a mirror in order to reflect light onto the specimen. Today, compound microscopes use their own light source, an innovation that allows scientists to work even in low ambient light conditions.

In general, bright field microscopes will have the following components:

- A base supports the entire body of the microscope. In simple microscopes, this base will hold the reflecting mirror, which can be adjusted in order to obtain a good amount of light to reflect onto the specimen. In compound microscopes, a light source is attached to the base, and the base will contain circuits and a plug which the microscope user can attach to a power source.

- The objective lens system of a microscope rests on a rotating carousel, so that the microscope user can switch from lower to higher magnifications as he or she views the specimen in greater detail.

- Bright field microscopes will commonly have four objective lenses. A simple objective lens can magnify the object four times, which is useful for establishing the field of view. Another objective lens can magnify the object ten times, which is useful for selecting which part of the specimen you would like to view. Another objective lens can magnify the specimen further, so that you can see your selected portions much better. Lastly, some microscopes have an oil immersion lens, which produces the highest magnification along with a drop of oil between the objective lens and the specimen.

- The ocular lens or lenses magnifies a specimen further; these lenses are the closes to the eyes, and these are the ones that the scientist looks through as he or she observes the specimen. Some microscopes are built with two adjustable oculars, which can be moved to fit the eyes of the scientist using the microscope.

- The microscope arm supports the objective lenses and the carousel, and connects them to the base of the microscope. In some microscopes, this arm can be adjusted so that the reflecting mirror can be given a wider range through which it can reflect light.

- The body tube sends light from the specimen to the ocular lens.

- A condenser lens can direct light to pass from the light source and through the specimen. In some microscopes, these condenser lenses can be fitted with colored glass that can increase contrast in the specimen.

- The microscope stage allows the slide to be mounted onto the microscope, and can allow the slide to be moved in different directions. The microscope stage will also contain the slide clips that will hold the slide in place and keep it from slipping off the microscope stage.

- Adjustment knobs allow the microscope user to focus on the specimen. The coarse adjustment knob moves the microscope stage up and down through large distances in order to gain focus on the specimen itself, while the fine adjustment knob moves the stage in smaller increments, allowing the microscope user to focus on the part of interest in the specimen.

What are the Limits and Advantages of the Bright Field Microscope?

Bright field microscopes are easy to set up, and they can be easy to use. In fact, many schools start students early in learning how to use the bright field microscope. Moreover, very little sample preparation is required, so that even live cells can be viewed. This is in contrast to electron microscopy, where specimens have to be killed, fixed, and then sectioned carefully in order to be viewed.

However, bright field microscopes allow only low contrast and magnification of biological samples, so that more sophisticated microscopy methods are often necessary to resolve finer details. Despite these limitations, a bright field microscope can still do a good job with basic studies in the life sciences. Thanks to the working parts of a bright field microscope, looking at an unseen world and learning from are made much easier.

The fields of microbiology and bright field microscopy have long been inseparable. When scientists first became interested in microbes, they had only very few tools to feed their curiosity and study the microbial world. What they had was a simple system of lenses and mirrors through which they could look at some bacteria or infected material. Today, even with the fields of molecular microbiology and DNA analysis developing rapidly and gaining even more popularity, bright field microscopy still remains as a laboratory technique to identify and characterize microbes.

Bright field microscopy is also one of the first fields that students of microbiology will find themselves immersed in. This is because many of the sophisticated concepts today arise because of knowledge acquired while studying microbes under the microscope.

What Can You See Under a Bright Field Microscope?

Microbiology is interested not only in bacteria, but in fungi, viruses, and other infectious agents such as worms, as well. Because microbiology relies so much on magnifying equipment, it has to constantly find ways by which microscopy can show even the minutest details of the microorganism of interest. Today, sophisticated microscopes such as electron microscopes can resolve details at the cellular level, allowing scientists to see even more of microbes than they ever have.

Bright field microscopy, however, has not gone out of fashion, and many microbiology students begin their studies by learning how bright field microscopes work. In a nutshell, bright field microscopes work by allowing light to pass through the specimen of interest, into a system of lenses, and to the eyes of the observer.

As such, magnification of a bright field microscope can at best reach a hundred times the original, and with the help of a drop of oil in between the lenses and the specimen. This oil prevents light from scattering out into the air, and can focus light rays directly into the lens, so that magnification is much higher.

Not all organisms, moreover, are visible under natural light. Many microorganisms are actually transparent, and the casual observer can miss them if they are not properly stained. Scientists have developed many different staining methods that will not only make microorganisms visible, but identify what proteins they might have as well.

For instance, in Gram staining, bacteria can be classified as either Gram positive or Gram negative. Gram positive bacteria appear purple under the bright field microscope after the staining process: these bacteria have thick cell walls, and also require certain antibiotics to be killed. Gram negative bacteria, on the other hand, will appear red or pink under the bright field microscope after the staining process: these bacteria have thinner cell walls, and will require another set of antibiotics to be killed.

Fungal spores are also visible under a bright field microscope, and these, in turn, need their own staining methods in order to be visualized. Although viruses cannot be magnified by a bright field microscope, their effects can be seen: when viruses escape a cell, they can cause it to rupture, an effect that you can see with proper staining and specimen sectioning techniques.

Scientists also use the bright field microscope to look at the effects of bacteria, viruses, fungi, or even worms on cells and cell systems. Some bacteria can weaken cell walls or cause cells to rupture. Some fungi can invade cells and cause certain morphological changes. Worms are easily seen under the microscope. For instance, scientists can look at blood samples under a microscope and point out bacteria, evidence of viral infection, worm eggs or cysts, and fungal spores.

What Can a Bright Field Microscope be Used For?

Because the bright field microscope can actually be powerful, it has many uses. In a basic microbiology laboratory, bright field microscopes are routinely used to look at the effects of Gram staining on bacteria. Identifying bacteria begins with basic laboratory methods such as Gram staining, and many peer-reviewed journals do not accept molecular microbiology papers if they are not supported by such basic techniques first.

In a diagnostic laboratory, bright field microscopes can be used to identify infectious microbes. Scientists can use blood, urine, or fecal matter as samples, place these samples on a slide, stain them, and then view them under the bright field microscope in order to see if any infectious organisms are present. Bright field microscopes can even be used in conjunction with special quantification slides: by counting bacteria present in a certain grid, scientists can calculate approximately how many bacterial cells are present in a sample.

In an ecology or food testing laboratory, bright field microscopes can be used to identify any contaminating agents in water or soil. In conjunction with more sophisticated quantification and identification systems, scientists use bright field microscopes to count how many microbes are present in samples, and what these microbes are.

These are only a few facts that link microbiology and bright field microscopy together. Science will always evolve to create better, bigger, and more complicated tools to study microbiology. However, bright field microscopy will always remain as an important laboratory tool.

Using a bright field microscope can be easy to many experienced scientists. After all, bright field microscopes are one of the most simple laboratory tools: through the use of visible light passing through the specimen and through a system of lenses, scientists can resolve a few details and learn a few things about specimens, from microbes to minerals. Capturing the image of the specimen, however, is a little more difficult; bright field microscopy and imaging techniques are still constantly being developed in order to make better tools that can help students and researchers alike.

There are many ways by which a bright field microscope image can be captured. In general, the captured image can be static or mobile. Each kind of image will have its own advantages and disadvantages, as well as its own ease of use.

Seeing Pictures

A bright field microscope has its own ocular lens, which is the last system of lenses that the light passes through before it reaches your eyes. The ocular lenses can be enhanced by adding on a camera. For most basic laboratories that are operating on a budget, this camera can be used to take photographs of the specimen being viewed. There are different cameras that you can fit onto a bright field microscope.

- A film camera offers the advantage of low cost, but not all details can be captured by such a camera. Moreover, film cameras need to be removed from a microscope more often in order to take out the used film and put in a new one. This can allow dirt, grime, and dust to enter the body of the microscope, which can hamper the function of the bright field microscope. The dirt, dust, and grime can even enter the ocular or objective lenses, causing images to blur.

- Most laboratories now use digital cameras for bright field microscopy imaging. Although digital cameras are more expensive, they can resolve specimens better, and they do not need to be removed from the microscope body so often. Some digital cameras can be connected directly to a computer, so that images are fed to the computer as soon as they are captured. Some digital cameras also allow viewing of the image from a computer screen, so that looking for details can be less straining on the microscope user.

- An alternative to these cameras is the Polaroid, which makes use of a rather bulky camera attached to a set of films. Once a picture is taken, it can be developed and viewed quickly. However, most Polaroid cameras for the laboratory take only black and white photographs, and resolution is often dependent on the amount of focus on the specimen. Moreover, Polaroid films are expensive.

Watching it on TV

Static images offer the advantage of budget, as well as easy reproducibility. Scientists also need static images in order to document their findings and report them in scientific journals. However, not all static images provide enough information on a specimen. If live specimens need to be examined and studied in detail, scientists need a camera system that can capture the living specimen without killing it or freezing it in time.

As a result, some microscope accessory merchants now provide video camera systems that can be attached to bright field microscopes. Such video camera systems can allow scientists greater versatility in studying specimens. In general, video camera systems can either use film or a digital medium.

- Film video cameras have the same disadvantages as film photography. However, film video cameras can be handy in the field, where computers cannot be brought, and where a microscope is needed to carry out studies on live specimens. Film video cameras can also record specimen movement or behavior, and these films can be played for classrooms without spending too much on playback equipment.

- Digital video cameras have the same advantages as digital photography, and although they are expensive, they can be advantageous to scientists who need to present their microscopy findings at conferences. Digital video files can simply be saved onto a computer, and then played at a conference for conference visitors and observers to look at and enjoy. Digital footage of specimens is also easier to send through the Internet, which is important for scientists working in different parts of the world, as it can expedite their research.

Video imaging techniques for bright field microscopy can be useful for many fields of science. They can show motile bacteria moving through its environment, which can allow scientists to see flagella movements and how the bacterium interacts with its surroundings. Videos can show heart cells in culture, which already beat and contract.

Bright field microscopy and imaging are still undergoing improvements. Although there are already more sophisticated methods of viewing specimens, live specimens need bright field microscopy in order to be viewed better. With basic microscopy and imaging going hand in hand, scientific study can be much easier for scientists, and more exciting and interesting for people waiting for findings.

References
Tortora, G. et al. Microbiology. 5th Edition. Benjamin Cummings.1996.
Campbell, N. Biology. 4th Edition. Benjamin Cummings. 1996.
Alberts, L. et al. Molecular Biology of the Cell. 3rd Edition. 1993.

Bright field microscopy is a basic tool in many laboratories interested in the life sciences. Microbiologists use bright field microscopes to carry out basic identification and quantification of microbes present in a sample. Diagnosticians use bright field microscopes to identify infectious microbes, and from their findings, make the proper diagnosis. In order to maintain a bright field microscope and make it even more powerful, scientists need bright field microscope accessories to help them out.

Bright field microscopes are the most simple tools used by scientists to aid them in their studies. However, they can show objects only at low magnifications, so that if more details are required, scientists must use more sophisticated magnification techniques, such as electron microscopy.

What are the Parts of a Bright Field Microscope? In a nutshell, a bright field microscope is a system of lenses that uses visible light to show specimens in greater detail. The entire bright field microscope is fitted onto a body, which contains a base that supports the entire microscope structure; a movable arm that supports the lenses and connects them to the base; and a body tube that allows light to pass from the specimen and into the viewer’s eyes. The specimen is held in place by slide clips that are mounted onto a microscope stage.

The system of lenses starts with the condenser, which directs light from the light source to pass through the specimen. Light then passes through one of often four objective lenses, which show the specimen in greater detail depending on their magnifying capabilities. Lastly, light passes through the ocular lenses, which magnify the image further. Some bright field microscopes are equipped with adjustable oculars that can allow scientists to adjust them to their own visual needs.

A microscope can be adjusted for better illumination and magnification. An electrical light source is often built into compound microscopes, but some microscopes still make use of adjustable mirrors that can capture light and reflect it onto the specimen. Adjustment knobs also allow the user to move the specimen farther or nearer the lenses. Coarse adjustment knobs move the specimen through large distances, while fine focus adjustment knobs move the specimen through smaller, finer increments.

What Can You Add On to a Bright Field Microscope? Many bright field microscope users need accessories to make their microscopes work better or show even finer details. Such accessories are often referred to as enhancements, and they are used by scientists working both in the laboratory and the field in order to allow a microscope to adapt to ambient conditions.

- Some microscopes can be fitted with an iris diaphragm, which can increase or reduce the amount of light that passes through the specimen. An iris diaphragm can even allow light to pass at an angle, so that some details can be seen per layer in the specimen.

- The carousel of objective lenses can be fitted with an oil immersion objective. An oil immersion objective lens prevents light scatter that can lower the magnification of a specimen: a drop of oil stands between the end of the lens and the specimen itself, with the drop of oil acting as an extension of the glass slide. This magnification technique can improve specimen resolution.

- Some microscopes are also fitted with light filters of different colors. Some specimen features cannot be seen under white or visible light, so colored filters can change the frequency of the light coming to the specimen. This is useful for scientists who need to look at samples of rocks or minerals.

- Some microscopes can be fitted with a special ocular lens that contains measurement grids or a scale. These tools can be used to estimate the size of a specimen. Some ocular lenses can also be fitted with special crosshairs that can aid in focusing on a specimen. You can also add a camera to capture images of the specimen being viewed.

How Can You Enhance Bright Field Microscope Viewing? Not all specimens are easy to see under visible light. In microbiology, seeing the complete details of a specimen are required not only to identify the specimen, but to see what molecules it may be producing. To visualize specimens, microbiologists use specific stains. Simple staining methods can allow microbiologists to see what microorganisms look like.

On the other hand, differential staining methods can allow scientists to actually identify and characterize microbes. Such staining methods can allow scientists to see important structures such as flagella or endospores. A special method known as Gram staining can even give scientists the chance to see what the bacterial cell wall is made of, and what antibiotics can kill that specific bacterium.

These are only a few bright field microscope accessories that scientists need in order to make their bright field microscopes better. For more advances accessories, you can talk to a bright field microscope vendor, who can make recommendations on how you can make your bright field microscopes serve your needs.