Also known as a stereoscopic microscope, low-power microscope, or dissecting microscope, it is a variation of digital optical microscopes that provides lower magnification images compared to a compound microscope. Its magnification power ranges from 2x-100x depending on the setup. Three-dimensional imagery is made possible by the presence of two distinct optical paths, two objectives, and eyepieces.
The presence of two light paths makes it possible for different light rays to travel and create separate images, which then offers viewing angles of varying degrees to the left and right eyes of the observer.
The best stereo microscope uses the reflected light rays from the specimen rather than the transmitted light. The three-dimensional view of a specimen gives access to more details during observation. This, therefore, makes it an invaluable tool for analyzing the external features of objects.
The invaluable nature of a stereomicroscope is evident since about 99% of stereo applications employ less than 50x magnifications. Stereomicroscopes are also known to possess longer working distances than compound microscopes.
History of a Stereo Microscopes
Since the earliest report of the microscope in the 16th century, microscopes have undergone significant modifications and perhaps transcended uses which the inventor intended for its creation. The application of the first microscope models was more or less restricted to the medical field. Today various microscopes are used in different professional fields for varying purpose.
One to note is the stereomicroscope which first came to light in the 19th century, albeit existing designs dated as early as the 17th century. This invention broke new ground in the field of sciences and transformed how scientists observed specimens
The first design of the stereo microscope was made by Cherubind’Orleans (1613-1697), a French scientific instrument maker. Cherubind’Orleans’ model which was tagged “a pseudo-stereo model” was released in 1677. It made use of supplemental lenses. The result was a projection of the left image of the specimen observed to the right eyepiece and the right image of the specimen projected to the left eyepiece.
John Leonard Riddell (1807-1865) later built on the work of Charles Wheatstone and published an advanced description of the principle, titled ‘On Binocular Microscope’ in the Journal of Microscopical Science.
The next model of the stereomicroscope followed in 1892. It had features that typical stereomicroscopes are known for today. Horatio SaltonstallGreenough (1845-1916), an American biologist, is credited with this achievement. His model was called the Greenough stereomicroscope. The majority of Greenough stereomicroscopes used dual Porro prisms. The internally reflective prisms provided erect images to the eyepieces from light paths which passed through two adjacent and separate objectives.
Greenough’s model became commercially available in 1896 after he collaborated with the Carl Zeiss Company to produce units of the prism in Jena, Germany. The Zeiss engineers introduced the inverted prism which created an erect image.
Working Principle of a Stereo Microscope
The working principle of a stereomicroscope is based on two light paths used in its objectives and eyepiece. It makes use of the natural, reflected, or episcopic light from the object to illuminate and magnify images at low power. Therefore, it is an ideal tool for observing opaque, thick, or solid objects like coins, fossils, mineral specimens, insects, flowers, etc.
The stereo microscope offers a very close observation of small specimens. The images usually appear larger than the original size due to an effect known as macro-photography.
The microscope works with two magnification systems; fixed (primary) magnification and zoom (pancratic) magnification. An optical system called the Galilean optical system exists between the fixed magnification and the zoom magnification. It possesses fixed-focus lenses that give fixed magnification for varying magnification sets; two sets of magnifications to four-magnifications, three sets to six-magnifications, and lots more.
Types of Stereo Microscopes
After knowing what is a stereo microscope, it is pertinent you know the different types of stereomicroscope out there. Here are the types of a stereomicroscope.
1. Stereo zoom Dissecting Microscope
This is a binocular or trinocular stereo microscope with a zooming range of 6.7x-45x. It makes provision for the attachment of a digital camera to captures photos of the specimen. It also features a rotatable (360°) dual-LED illuminator.
2. Stereo zoom Boom Stand Microscope
This is a type that comes with a larger base and stage. It boasts LED lightening and optional dual-pipe lightning. Its magnification range is between 6x-45x. Its magnification can also be changed by adding auxiliary lenses or eyepieces.
3. Digital Tablet Dissection Microscope
This is a high-end dissecting microscope with a touch screen LCD tablet camera capable of a zooming range of 6.7x-45x. The top and bottom of this microscope house inbuilt LED lights designed to enhance images captured by its 5.0-megapixel digital camera.
4. Dual Power Dissecting Microscope
As the name implies, this stereomicroscope is capable of producing images at a magnification of two separate powers. Its common types are the 10x/30x and 20x/40x variations. It comes with a 360° rotation ability designed to enhance the focusing and viewing of a specimen. A key feature of this stereomicroscope is the pair objectives. They are parfocalled, parcentered, and achromatic.
5. Single Magnification Handheld Pocket Microscope
Manufactured in Japan, this is a single-powered handheld stereomicroscope that has two magnification powers and does not require light. It possesses an optical glass of very high quality with ease in usability and its moderate size makes it very portable.
Parts of a Stereo Microscope and their main functions
1. Stand (Arm)
This is sometimes referred to as the ‘backbone of the microscope because it connects the head part of the microscope to the base, providing support to the head part. The stand of a stereomicroscope may be a hollow, cylindrical rod or a rigid arm that looks like elongated cuboids, depending on the microscope type.
The stand consists of a power cord used for incident illumination which may be found on the upper-most part of the stand. This allows the illumination of the specimen from above. It may also consist of the ‘arm track’. This permits the up and down movement of the microscope head during viewing. The arm track is usually located at the front part of a rigid stand.
Main functions of the stand (arm)
- Supporting the head: The microscope head is held in place as movement occurs during the viewing of a specimen because the stand connects the head to the base of the microscope.
- Focusing: The user of a stereomicroscope can focus on an object that is being observed by turning the focus knob. On a hollow cylindrical rod stand, the knob is not directly located on the stand, but on a rigid microscope stand, a coarse focus knob is found on the stand.
- Housing the power cord: The power is usually found at the top of the stand. However, the stand doesn’t hold the power cord in all stereomicroscopes.
- Lifting/carrying the stereomicroscope: It is often recommended that users move the tool by the stand and base because the stand is solid which makes it convenient for moving or lifting the microscope.
2. Base
This is a heavy, lower part of the microscope that provides support to all other parts of the microscope due to its width and heavy nature. It, therefore, provides stability for the microscope when it is placed on a table.
Main functions of the base
- Support: The base of the microscope provides stability for the entire device. It maintains balance and ensures that the device doesn’t fall over.
- Stage: In a stereomicroscope, the base also acts as the stage, which is the part of the microscope on which a specimen is a place for observation.
Other parts of the stage include:
- The on/off switch: This is usually located on the right side of the microscope base and is used to turn the illuminator on or off.
- Light intensity regulator (Rheostat light control): This is used to adjust the intensity of the light by either increasing or decreasing the brightness. Microscopes with only an overhead light source have only one light intensity regulator, while there are two light intensity regulators present in a microscope that has both the stage and overhead light sources.
- Stage light: The stage light is housed within the base. It comprises a clear glass plate held in place by a tight screw that allows light to pass through it and reach the specimen.
3. Microscope Head
The head is also known as the body of the microscope. It contains the upper optical part of the microscope and consists of several moveable parts. The moveable parts of the microscope head, therefore, make it a very delicate part of the microscope.
Main parts of the microscope head and their functions
- Eyepieces (Ocular lenses): The eyepieces function as magnifiers to enlarge images projected from the objective. This allows observation of more details due to the increase in the size of the specimen under study. Some eyepieces include the eye lens, field doublet, lens doublet, and lens triplet. While simpler eyepieces may consist of the eye lens and field lens only.
- Objectives: These are arguably the most important part of a stereomicroscope. This is because they are the main lenses responsible for magnification of specimen, gathering light, and producing the images projected on the eyepieces. The most common material used for objective lenses is glass. The objectives are housed in a cylindrical cone which can be turned to adjust the magnification.
- Auxiliary lenses (Barlow lenses): Some stereomicroscopes make provision for the use of an auxiliary lens such as a Barlow lens, which can be used to increase or decrease the total magnification of the microscope by a fixed factor.
4. Adjustment knobs
These adjustment knobs (separate from those located on the base) could either function as focus knobs or zoom knobs. Focus knobs raise or lower the microscope head to increase the working distance. Zoom knobs help to zoom into a specific area of interest. They are usually found on both sides of the microscope head beneath the eyepieces.
5. Prism, Relay lens, and Reticle
The prism is responsible for the refraction of light which changes the orientation of the image. The relay lens inverts the image formed and also extends the imaging system. Unlike the reticle which is a graded tiny piece of glass used for measurements.
6. Digital camera
This is a component found in most stereomicroscopes used to record or capture the image of the observed specimen.
How to use a Stereo Microscope
Here are some essential tips to ensure effective use of a stereomicroscope:
1. Install the appropriate stage
Two types of stages may be used depending on the stereomicroscope. The opaque black/white stage or the clear/frosted glass. The former is commonly used in observing specimens that do not allow penetration of light while the latter allows light underneath the specimen mounted on the slide to illuminate the specimen so that the light is then received by the objectives above the specimen.
2. Turn on the stereo microscope
Once the appropriate stage is installed, you may then proceed to turn the device on, after which you also turn on the incident or transmitted illumination of the stereomicroscope (or both) depending on the specimen to be observed.
3. Adjust the head/body of the stereo microscope
This helps to set a starting point for the observation. This is achieved by using the focus knob carefully to lower the head/body, which holds the objectives all the way down to the bottom.
4. Adjust the interpupillary distance
This is done by pulling the two eyepieces apart or pushing them close together gently, inwards or outwards, so that the two fields of view become one. Correct adjustment produces a single circle when viewing through the eyepieces.
5. Mount the specimen and adjust the focus
Ensure appropriate illumination for the specified specimen. Place the specimen at the central part of the stage, hold the glass slide with stage clips if necessary, and slowly raise the microscope head using the focus knob until the image of the specimen becomes clear.
6. Zoom in
Once a clear image has been gotten, the zoom knob can be used to zoom into a particular area of the specimen for better viewing. The light intensity can also be decreased or increased as the case may be, to improve image quality.
7. Turn off the stereo microscope after the viewing
After the viewing process has been completed, it is best to return the zoom function to its lowest setting. Lower the light intensity, turn off the device and cover it with a suitable bag.
Applications of a Stereo Microscope
Uses of stereomicroscopes are not limited to but include the following:
- Dissecting objects or even performing microsurgery in hospitals due to its long working distance.
- Analysis and cleaning of fossils in Paleontology.
- Examination of the morphological structure of insects in Entomology.
- Study of the nature of flowers and other plant structures in Botany.
- Inspection of bone fractures in Fractography.
- Studying the topography of solid samples.
- Manufacturing of watches.
- Inspection and repair of circuit boards by technicians.
- Examination of infections in pathological laboratories.
- Analysis of fabric and textiles by specialists in the textile industry.
Final Thoughts
Since the invention of the first stereomicroscope, subsequent models have seen significant modifications. However, inventors made sure to retain a key feature of the stereomicroscope, which is perhaps its defining feature; the ability of the stereomicroscope to produce three-dimensional images.
Generally, stereomicroscope types can be configured to meet the specific needs of their users, which make a case for its use across many fields. Despite the high cost of acquiring a stereo microscope, being a multipurpose tool makes it an ideal tool for observing opaque, solid, and whole specimens.