What are the different types of biological microscopes?

In this article, we will review the various subtypes of biological microscopes, such as head types, lighting method types, illumination technique types, and more. Although some of the concepts discussed in this article apply to other types of light microscopes, we will only focus on the different features as they pertain to biological microscopes. By the end of this article, we are confident you will be able to pick the best biological microscope for you and your application.

MICROSCOPE HEAD

A microscope head is the assembly that houses the entire eyepiece and the top of the drawtube. Sometimes the microscope head is rotatable and can be used in different orientations. The number of eyepiece (oculars) lenses distinguishes whether it’s a monocular, binocular, or trinocular microscope. As you add complexity, the price increases but you also add benefits to imaging that may be useful depending on your needs.

Now, when searching for the right head type for studying cells, microorganisms, and biological specimens, you’re probably going to wonder “what is the difference between a monocular microscope versus a binocular microscope versus a trinocular microscope”? Let’s break that down next.

Monocular Microscope

A monocular microscope has a single eyepiece for observation. The observer must close one eye to view the specimen, which can create some discomfort when viewing scientific specimens for longer time periods. It’s commonly used in educational institutions for basic microscopic examination.

Monocular microscopes are the most common type of microscope, and the lowest cost, so they are great for the beginner or casual user. Also, if you want to upgrade your eyepiece, you’ll only need to buy one.

Binocular Microscope

A binocular microscope has two eyepieces that allow both eyes to observe the specimen at the same time. This type of microscope offers greater comfort for extended use and better depth perception due to the stereoscopic effect. It is preferred for advanced applications, such as professional research and laboratory work.

With a binocular microscope there’s a bit more setup, as you must adjust the interpupillary distance (IPD) between your two eyepieces by rotating the tubes closer or farther apart, so that the two images form into a single image.

Trinocular Microscope

A trinocular microscope has three eyepiece positions. Two are for the observer and the third is used for image capture, photography, or video recording. The third eyepiece usually connects to a camera or other recording device. This type of microscope is commonly used for research, clinical, and industrial applications that require image documentation and analysis.

There are USB cameras and WIFI microscope cameras that can attach to the trinocular port and transmit the data to your computer or phone. An alternative to this is an eyepiece camera that can be used in any of the above models, by simply replacing the eyepiece with a USB eyepiece camera.

Ultimately, your budget and comfort level will dictate which microscope head will work best for you and your research needs.

LIGHTING METHOD

When choosing between a reflective and transmitted light microscope, you’ll need to understand what types of specimens you’ll be examining and the information you’re hoping to learn from the various subjects you’re studying. But, what is the difference between a reflective light microscope and a transmitted light microscope?

The main difference between a reflective light microscope and a transmitted light microscope is the way in which the specimen is illuminated and observed. Typically this is easy to recognize in your microscope, if there is a light source above your specimen, it’s reflective. If the light source is below, then its transmitted. Some microscopes can have both a reflective light source and a transmitted light source which is the most powerful option to look at any type of specimen.

Again, the choice of microscope depends on the type of sample and the information you’re required to collect for your study. Reflective light microscopy is best suited for observing opaque or reflective samples, while transmitted light microscopy is ideal for examining thin or transparent samples.

Reflective Light Microscope

In a reflective light microscope, the light source is located above the specimen and reflects off the surface of the sample to be observed. The reflected light is then collected by the objective lens and viewed by the eyepiece. Reflective microscopes are commonly used for inspecting opaque or reflective samples such as:

• metals
• ceramics
• some biological tissues

Transmitted Light Microscope

In contrast, a transmitted light microscope illuminates the specimen from below, and the light passes through the sample before it’s observed. This type of microscope is used to inspect thin or transparent samples, such as:

• cells
• tissues
• microorganisms

A transmitted light microscope typically uses a brightfield illumination technique, but it can also use other techniques such as darkfield, phase contrast, and fluorescence microscopy.

ILLUMINATION TECHNIQUE

Illumination techniques used in microscopes to visualize specimens are called bright field, dark field, phase contrast, and fluorescent. A microscope can be specific to a certain illumination technique such as a bright field microscope or can have multiple options that the user can switch between. Let’s explore what the difference is between a bright field, dark field, and phase contrast illumination in a microscope.

Brightfield

Brightfield, the most common illumination technique, uses a bright background to view the specimen. This is achieved by passing a beam of light through the specimen and into the objective lens. The image produced by this technique is based on the absorption and reflection of light by the specimen. Brightfield microscopes are the most popular type by far.

Darkfield

When using a dark background to view a specimen it’s considered the darkfield illumination technique. This is achieved by blocking the central beam of light, so only the scattered light from the specimen enters the objective lens. The scattered light produces a bright image of the specimen on a dark background. This technique is useful for visualizing specimens that aren’t visible with bright field illumination, such as small, transparent, or low-contrast objects.

Phase Contrast

Phase contrast illumination is a technique that enhances the contrast of transparent and colorless specimens by exploiting differences in refractive index (how much light bends when passing from one medium to another). In this technique, the light passing through the specimen is shifted out of phase, and the resulting interference pattern is used to create an image with high contrast. Phase contrast microscopy is commonly used to study living cells, including bacteria and other microorganisms, which are often difficult to see with other techniques.

Fluorescent

Fluorescent illumination is a technique in fluorescence microscopes that uses specific dyes to produce images of the sample. This technique involves using a special light source that emits a specific wavelength of light that is absorbed by the fluorescent dye. This causes the dye to emit light of a different wavelength, which is detected by the microscope. This technique is particularly useful for observing specific parts of the sample, such as proteins or DNA.

Oftentimes, these different lighting techniques are done using transmitted light, but the transmitted light is manipulated differently to achieve the certain illumination technique. For example, a phase contrast microscope usually has both brightfield and darkfield modes. Overall, the choice of illumination technique depends on the type of specimen and the features of interest. Each technique has its advantages and limitations and depending on what you’re studying will dictate whether you will use a darkfield, brightfield, fluorescent or phase contrast approach.