What Is The Use Of A Compound Microscope?

Definition and Image Formation

A compound microscope is a type of optical microscope that uses visible light and multiple lenses to help you observe a real and magnified image of tiny objects.

A compound microscope is defined as a microscope with a high resolution and uses two sets of lenses providing a 2-dimensional image of the sample.

Through a compound lens system, it produces enlarged images of microscopic objects like living and dead organisms, tissues, and cells.

Compound microscopes used for studying biological specimens are also called biological microscopes.

A microscope is an instrument that can be used to observe small objects, even cells. The image of an object is magnified through at least one lens in the microscope. This lens bends light toward the eye and makes an object appear larger than it actually is.

• Difference between simple and compound microscope is that a simple microscope uses only one lens while the compound microscope uses more than one lens.
• Compound microscopes use multiple lenses to magnify objects with greater clarity.
• Compound microscopes use transmitted light illumination, where light passes through the sample.
• They provide high magnification (40x to 1000x or more) and offer a single optical path, allowing the same image to be viewed with either eye.
• Compound microscopes typically provide magnification in the range of 40x-1000x.

Compound microscopes are used to view small samples that can not be identified with the naked eye. These samples are typically placed on a slide under the microscope.

Objects and Specimens

The compound microscope is typically used for observing objects at the cellular level.

The compound microscope is mainly used for studying the structural details of cell, tissue, or sections of organs.

These microscopes are ideal for observing tiny objects like cells, biological structures, and microstructures in materials like metals, rocks, and textiles.

1. The identification of diseases becomes easy in pathology labs with the help of a compound microscope.
2. Forensic laboratories use compound microscopes for the detection of human fingerprints.
3. The presence of metals can be detected with the help of a compound microscope.
4. The study of bacteria and viruses becomes easy with the help of a compound microscope.
5. Schools use compound microscopes for academic purposes.

Medical research: used to examine bacteria, cells, and tissues.

Biological studies: helps scientists study microorganisms and biological samples.

Forensic science: assists in analyzing tiny evidence such as fibers and blood samples.

Pharmaceutical research: used for drug development and quality control.

Education & research: used by students and scientists to explore microscopic details.

• Polarizing compound microscopes are used to examine chemicals in the pharmaceutical industry.
• Petrologists and geologists use polarizing microscopes to examine minerals and thin slices of rocks.
• Darkfield microscopy is a specific technique that back-illuminates a sample in order to highlight specific features of the sample such as hairline metal fractures or flaws in precious stones.
• Fluorescence microscopes and DIC (differential interference contrast) are other types of compound microscopes.
• These are biological microscopes that use different light wavelengths to fluoresce a sample in order to study the specimen.

Light and Lenses

The optical parts of a compound microscope include a mirror, eyepiece lens, and objective lenses.

The light is made to pass through the thin transparent object. A magnified image of the object is obtained by the objective lens. This image is known as the real image. The eyepiece or the ocular lens then magnifies the real image more and is viewed as the virtual image.

The compound microscope is also known as the bright-field microscope because the light passes directly through the light source to the eye through the two lenses. This mechanism makes the field of vision brightly illuminated.

Objective lenses

They’re attached to the nosepiece at the base of the body tube. They can be of many types — scanning (4x magnification), low power (10x magnification), high power (40x magnification), oil immersion (100x magnification), and specialty (2x, 50xoil, 60x, and 100xdry magnification).

Eyepiece lens

The eyepiece or ocular lens is attached to the top of the body tube. The rim of the eyepiece contains markings such as 5x, 10x, 15x, and 20x, which denote its magnification power.

Condenser lens

Focuses light onto the specimen for clearer imaging.

Diaphragm

Controls the amount of light passing through the specimen.

The mirror reflects rays from an external light source into the microscope. Compound light microscopes have their own light source (illuminator) attached to the microscope base. The light rays are focused onto the stage by the condenser, which is placed below the stage.

Microscope lenses use transmitted, refracted, or reflected light to increase the image size of the object being viewed. This aspect is called magnification. The magnification power of a microscope depends on the lenses’ ability to bend light waves.

Magnification and Resolution

Higher magnification is achieved by using two lenses rather than just a single magnifying lens.

The total magnification that a certain combination of lenses provides is determined by multiplying the magnifications of the eyepiece and the objective lens being used. For example, if both the eyepiece and the objective lens magnify an object ten times, the object would appear one hundred times larger.

The total magnification of a compound microscope is calculated by multiplying the objective lens magnification by the eyepiece magnification level. So, a compound microscope with a 10x eyepiece magnification looking through the 40x objective lens has a total magnification of 400x (10 x 40).

• Objective lenses: there are usually 3-5 optical lens objectives on a compound microscope each with different magnification levels.
• 4x, 10x, 40x, and 100x are the most common magnifying powers used for the objectives.
• The ocular lens is also known as the eyepiece.
• There are four types of magnification that can take place in the ocular lens: 5x, 10x, 15x, 20x.
• Compound microscopes can have up to four objective lenses of different magnifications, and the microscope can be adjusted to choose the magnification that best suits the viewer’s needs.

The object’s image must not only be enlarged but also its minute details must be clearly visible to the viewer’s eye. This aspect is called resolution. The clarity of the image produced depends on the lens quality and the frequency of the light waves falling onto the specimen.

Lenses with high magnification power also tend to provide greater resolution.

Thus, as the image size increases with the magnification power, more details become visible.

The lower the magnification, the smaller the image seen in the eyepiece. As the magnification increases, the size of the image gets bigger although the size of the hole in the eyepiece remains unchanged.

Mechanical Components

The mechanical parts of a compound microscope include a U-shaped base that supports the weight of the microscope.

• Arm: supports the microscope head and attaches it to the base.
• Nosepiece: holds the objective lenses & attaches them to the microscope head. This part rotates to change which objective lens is active.
• Base: bottom base of the microscope that houses the illumination & supports the compound microscope.
• Stage or platform: the platform upon which the specimen or slide are placed.
• Stage clips or mechanical stage: clips on the stage that hold the slide in place on the mechanical stage.
• Coarse and fine adjustment controls: adjusts the focus of the microscope.

The base is also known as the foot which is either U or horseshoe-shaped. It is a metallic structure that supports the entire microscope.

The connection between the base and the arm are possible through the pillar.

The stage is the metallic platform that is fitted to the lower part of the arm with a hole in the center. The microscopic slides are placed on the stage either by using side clips or by mechanical stage clips.

The main purpose of the body tube is to hold the objective and ocular lenses at the two ends. The end where the ocular lens is present is known as the head while the end where the objective lens is placed is known as the nose piece.

To bring the object under focus, the rack and pinion are either attached to the body tube or the stage.

These are two pairs of adjusting screws that are used either for a coarse adjustment or for fine adjustment. When a fine adjustment is made, the body tube or the stage moves extremely short distances while in coarse adjustment, the body tube and stage move up. Through fine adjustment, a sharp image can be obtained.

Compound and Stereo Images

A compound microscope provides a two-dimensional image, while a stereo microscope provides a three-dimensional image.

The dissecting microscope provides a lower magnification than the compound microscope, but produces a three-dimensional image. This makes the dissecting microscope good for viewing objects that are larger than a few cells but too small to see in detail with the human eye.

Compound microscope

In the compound microscope there is a single path of light that travels in a way such that it splits before reaching the eyepiece.

Stereo microscope

In a stereo microscope there are two objective lenses that are used for magnification. Each lens captures the image individually, which means that there is a requirement of two paths of light for the creation of a 3D image of the sample.

Binocular microscopes

More comfortable for extended use and suitable for higher magnifications.

Trinocular microscopes

Includes a camera port for capturing images and videos.

This also means that the sample must be translucent enough so that the light passes through it and every eyepiece contains the same image.

When using a stereo microscope, there is more room under the microscope for larger samples such as rocks or flowers and slides are not required.

A zooming microscope is defined as a microscope that comes with a knob that is used for adjusting the magnification.

A fixed power microscope is defined as a microscope that has a number of objectives but lacks a knob that can be used for magnification. Most of the compound microscopes have fixed power magnification.