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Bright field Microscope: Facts and FAQs

You might be wondering what a brightfield microscope is, but chances are, you have already seen one- more specifically, a compound light microscope. The thing is, brightfield microscopes are really common and can be found in just about any lab and science classroom.

These microscopes operate through a basic form of optical microscopy, and are commonly used to view and study naturally pigmented and artificially stained fixed or living specimens such as cells and tissue sections.

First, it’s important that you understand what bright field microscopy is, because it is the underlying principle that makes a brightfield microscope work. Here is a simple explanation of bright field microscopy:

What is bright field microscopy?

Bright field microscopy is one of the many types of imaging techniques used in microscopy. To be more specific, it’s one of the four types of light microscopy, which includes dark field microscopy, phase microscopy, and fluorescence microscopy.

In fact, it’s the most elementary form of microscope illumination method, since it simply requires a light source to illuminate the specimen being viewed under the microscope. This simplicity is also why it’s the first kind of microscopy taught in school.

This type of microscopy is most commonly used for compound light microscopes. As a matter of fact, many light microscopes are interchangeably referred to as brightfield microscopes. Bright field microscopy essentially works as a dark specimen is contrasted by a bright field of white light from the viewing area.

What is a brightfield microscope?

A brightfield microscope is basically any type of light microscope that makes use of an illumination technique called bright field microscopy. 

This kind of microscope has its own light source that provides illumination to the specimen, as well as at least one lens to magnify the image of that specimen. Common examples of brightfield microscopes are simple microscopes and compound light microscopes.

Below are important information on what a brightfield microscope is used for and how it works:

What is a brightfield microscope used for?

Brightfield microscopes are highly important in a variety of scientific fields, especially in the life sciences such as microbiology and bacteriology. Its simple yet versatile nature makes it a great imaging tool that can be used to study not only fixed specimens, but living cells and microorganisms as well. 

Moreover, these microscopes can also be used in medical sciences, forensics, and other industries that deal with small, thin, and semi-transparent specimens. It’s invaluable in the field of hematology and various biomedical analyses.

What are the parts of a brightfield microscope?

Parts of a brightfield microscope

Brightfield microscopes are made up of several different parts, and what these depend on what type of brightfield microscope you are looking at. That said, the most essential parts are the light source and the lenses.

The illumination or light source should be powerful and variable, with adjustment knobs for controlling the quantity and focus of the light. Meanwhile, the lenses are what magnifies the specimen to a certain level of magnification.

For example, compound light microscopes have compound lenses- an objective lens and an ocular lens. Each of these lenses vary in magnification ranging from 4x to 100x, and compounded, gives the microscope a high level of total magnification.

How does a brightfield microscope work?

Here is a detailed overview of how brightfield microscopy works on a typical light microscope, once the specimen is mounted on a glass slide which is then loaded onto the stage of the microscope.

Note that the process detailed below applies to compound light microscopes, and in a more basic manner, to simple microscopes. Other microscopes that make use of bright field microscopy may follow slightly different methods.

Step 1: Illumination 

First, the light source at the bottom illuminates a lens beneath the stage, called the condenser, and this light is focused by the iris diaphragm so that everything is clearly directed towards the specimen right through the stage’s aperture.

Step 2: Absorption 

What happens next is some of the light gets absorbed by the specimen’s dense areas, natural pigmentations, and any applied stains or dyes. This uneven passing through and absorption of light is what lets you see the intricate details of that specimen.

Step 3: Magnification 

Then, the light that passes through the specimen is collected by the objective lens on top, which is what magnifies the image, and this resulting image gets transmitted through the body tube and right onto the eyepiece, which is also a lens that further magnifies this image.

Magnification guide:

Here is an easy guide on the necessary magnification level for various specimens:

  • Low to moderate magnification (40x to 400x)- protists and metazoans, algae, other microscopic plant materials, pond water, and thick tissue sections
  • High magnification (400x to 1000x)- blood, condensed chromosomes, organelles, and fixed bacteria.

What are the advantages of using brightfield microscopes?

Pretty much nothing else in microscopy rivals a bright field microscope when it comes to its simplicity and versatility. Brightfield microscopes are relatively small, lightweight, and easy to use, not to mention grossly inexpensive as compared to other types of microscopes.

Generally speaking, brightfield microscopes are high power, high magnification, and high resolution imaging devices that are easy to operate and easy to upgrade with modern technological advancements.

What are the advantages of using brightfield microscopes?

Easy specimen preparation

There also isn’t much in the way of preparing and adjusting specimens for viewing, except for the occasional staining or dyeing of low contrast specimens for a better viewing experience, which in itself is a quick and simple procedure- as long as you are familiar with the proper staining technique the specimen requires.

Specimen monitoring

When working with single cells and small particles, bright field microscopy allows you to label the live specimen with colloidal gold nanoparticles, so it can be tracked for a certain period of time, enabling you to observe and record its motion, growth, activities, and interactions with the environment.

What are the common issues with brightfield microscopes?

While it’s true that a brightfield microscope offers a lot of uses across several disciplines, it also doesn’t come without its fair share of issues. For one thing, while it’s a great imaging tool for living microorganisms, it doesn’t work with live bacteria. 

Another thing is, it’s often hard to retain good image resolution as the magnification level of the microscope goes higher. And, low contrast specimens are difficult to view in detail, regardless of how focused the light source is, while too much contrast results in image distortion. 

But, the good thing is there are plenty of solutions that address these issues, including the following:

Lighting the specimen

When it comes to illumination, what’s important to remember is that high magnification requires intense illumination, while lower magnification works better with lower light levels. This is also why older microscopes that make use of a mirror as their “light source” are only capable of low magnification powers. 

Bright halogen and LED bulbs are what makes it possible to achieve magnification levels of 1000x or higher. Having said that, it’s important to be careful in using intense lighting, since this can heat up, damage, or kill the specimen.

Using special lenses

High magnification levels should always be complemented with an ultra-focused light, which is what makes for a clear image. 

This high resolution that we are talking about can be achieved with the use of oil immersion objective lenses, which has the ability to radically increase the microscope’s resolving power, since the objective lens is coated in a transparent oil that has a high refractive index.

Staining the specimen

One small problem is that most organic specimens, such as cells and bacteria, are either fully transparent or opaque, which results in a drastically low contrast when viewed under the microscope. 

Thus, making use of certain dyes and staining techniques is important to highlight the details you want to see. Afterwards, you can view the specimen in high resolution at magnification levels of up to 1200x when you use an oil immersion objective lens.

Using polarizing filters

Apart from or along with staining the specimen, additional illumination techniques may be employed to view the specimen better, such as by using polarizing filters that let you see certain details that may otherwise not be visible under white light.

Other than that, there really is so much more that you can do with a brightfield microscope. This simple yet versatile device is readily adaptable to a variety of new technologies and devices to further improve its function and versatility.

The future of bright field microscopy

The beauty of bright field microscopy is that it can easily be paired with modern technologies such as digital imaging systems to immortalize high resolution images of the specimen, as well as video imaging technologies to track the growth and interaction of a live specimen.

Moreover, it can also be modified and partnered with other imaging technologies to allow for three dimensional images that can be viewed in real-time. And, it has the capability to serve as a suitable alternative to fluorescence microscopy.

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