Aim: To study the parts, principles of microscopy, and resolving power of the simple and compound microscope

The optical microscope often referred to as the light microscope, is a type of microscope that uses visible light and a system of lenses to magnify images of small subjects.

There are two basic types of optical microscopes:

1. Simple microscopes

2. Compound microscopes.

Simple Microscope

Simple Microscope: A simple microscope is one that uses a single lens for magnification, such as a magnifying glass while a compound microscope uses several lenses to enhance the magnification of an object. It uses a lens to enlarge an object through angular magnification alone, giving the viewer an erect enlarged virtual image. The use of a single convex lens or groups of lenses is found in simple magnification devices such as magnifying glass, loupes, and eyepieces for telescopes and microscopes. It is actually a convex lens of small focal length, which is used for seeing the magnified images of small objects.

Working Principle of Simple Microscope

A simple microscope works on the principle that when a tiny object is placed within its focus, a virtual, erect, and magnified image of the object is formed at the least distance of distinct vision from the eye held close to the lens.

Structure of compound microscope

Simple microscopes are consist of two important parts, includes;

1. The Mechanical Parts

2. The Optical Parts

1. The Mechanical Parts:

The Mechanical Parts support the optical parts and help in their adjustment for focusing the object. They include the following components;

i. Metal Stand: It has a heavy base plate and a vertical rod fitted to it.

Function of Metal Stand: Metal Stand provides support and stability to other parts of the microscope.

ii. Stage: It refers to a rectangular metal plate fitted to the vertical rod. The Stage also has a central hole for light to pass from below. Some simple microscopes have a pair of slanting wings projecting from both sides of the stage which provide support to the hand for manipulating the object.

Function of stage: The specimen slide place over it to be observed.

iii. Base: The bottom portion of the simple microscope is known as the base. This portion provides supports to the microscope.

iv. Stage clips: located at the stage of the simple microscope; helps to hold the specimen slides in the proper place.

v. Adjustment screw: It is used to adjust the focus on the specimen.

2. The Optical Parts

The optical parts help in the magnification and visualization of the specimen. This part is consist of the following components;

i. Mirror: It has a plano-convex mirror, which is located is below the stage to the vertical rod by means of a frame.

Function: The primary function is to focus the surrounding light on the object being examined.

ii. Lens: Simple microscopes have a biconvex lens which is located above the stage, to the vertical rod, by means of a frame. For proper focusing, the lens can be moved up and down by the frame.

Function: It magnifies the size of the object and the enlarged virtual image formed is observed by keeping the eye above it.

A modern simple microscope contains the following parts;

Eyepiece: A set of lenses, located at the top of a microscope, which is used to visualize the samples. It has a magnification power of 10X to 15X.

Tube: It connects the eyepiece to the objective lenses.

Revolving nose-piece: The Revolving nose-piece or turret holds the objective lenses and it can rotate during the study of the sample.

Fine adjustment knob: The fine adjustment knob is used to focus on oil.

Applications of Simple Microscopes

There are present different uses of simple microscopes such as;

1. In Jewelry making shops, Jewelry makers used it to visualize the magnified view of the small parts of the jewelry.

2. In the Watchmaking industry, watchmakers used it to magnify a tiny part of the watch.

3. In the Agriculture sector, it is used to magnify various particles of various types of soils.

4. Palmist used a simple microscope to visualize the lines of the hands.

5. In Dermatology, a dermatologist or skin specialist used it to check for various skin diseases.

6. In Microbiological experiments, a microbiologist used it for examining and studying microscopic fungi, algae, and other biological specimens that are difficult to visualize using the naked eyes.

7. It is also used to visualize the details of stamps and engravings.

8. It also used to check the texture of fibers or threads of a cloth.

Magnification of Simple Microscope

The magnifying power of a simple microscope is given by:

M = 1 + D/F

Where

D = the least distance of distinct vision

F = focal length of the convex lens

The focal length of the convex lens should be small because the smaller the focal length of the lens, the greater will be its magnifying power. The maximum magnification of a simple microscope is about 10, which means that the object will appear 10 times larger by using the simple microscope of maximum magnification.

Compound microscopes

A compound microscope achieves higher levels of magnification than a stereo or low-power simple microscope. It is used to view smaller specimens such as cell structures which cannot be seen at lower levels of magnification.

Working Principle of Compound Microscope:

The compound microscope works on the principle of a combination of two convex lenses. Light from a light source (mirror or electric lamp) passes through a thin transparent object. The objective lens produces a magnified real image first image) of the object. This image is again magnified by the ocular lens (eyepiece) to obtain a magnified virtual image (final image), which can be seen by the eye through the eyepiece. As light passes directly from the source to the eye through the two lenses, the field of vision is brightly illuminated.

Structure of compound microscope

• A compound microscope is a laboratory instrument with high magnification power, which is consists of more than one lenses.

• Compound Microscopes are used for the study of structural details of a cell, tissue, or organ in sections.

• A compound microscope can magnify the image of a tiny object up to 1000.

• The term compound means “multiple” or “complex”. The compound microscopes are consist of two lenses i.e., the objective lens (typically 4x, 10x, 40x, or 100x) in a rotating nosepiece closer to the specimen, and the eyepiece lens (typically 10x) in the binocular eyepieces.

• A compound binocular microscope is more commonly used today.

• Zacharias Jansen created a compound microscope that used collapsing tubes and produced magnifications up to 9X.

• Compound microscopes are generally types of bright field microscopes. Compound microscopes may be categorized as an upright microscope and an inverted microscope.

• Upright compound microscopes are just like an ordinary microscope which has a lens system, followed by the stage where the specimen is kept, and then the light source.

• Inverted compound microscopes are exactly the reverse replica of the upright microscope with the illumination system first, followed by the stage, and then the lens system.

Types of Compound Microscope

Compound Microscope may be classified as

A. Light Microscope: Light Microscope is further classified into four categories such as;

1. 1. 1. 1. Bright-field Microscope

         2. Dark-Field Microscope

         3. Phase-contrast Microscope

         4. Fluorescent Microscope.

B. Electron Microscope: Electron Microscope is further classified into two categories such as;

1. Scanning Microscope

2. Transmission Microscope

C. Confocal Microscope

Mechanism of Compound Microscope:

Compound microscopes create an image of the specimen by these following steps;

• First of all, a specimen is placed between the objective and condenser lens.

• The light emitted from the light source is pointed over the specimen with the help of a condenser lens.

• After that, the light is passed through the specimen and comes towards the objective lens.

• The objective lens captures the light coming from the specimen and creates a magnified image of the specimen, which is called the primary image.

• Then the objective lens passed this image through the body tube to the ocular lens or eyepiece and again magnifies the image.

• At last, the viewer can see a clear and magnified image of the specimen through the eyepiece.

• Occasionally or during use of a 100x objective lens oil immersion method is used to produce a highly magnified image of the specimen. In this method, a drop of immersion oil is placed between the objective lens and specimen slide.

Magnification Power of Compound Microscope

The total magnification of the image formed by the compound microscopes is calculated b the following formula;

m = D.L/ f_o. f_e

Where, D = Least distance of distinct vision (25 cm)

L = Length of the microscope tube

fo = Focal length of the objective lens

fe = Focal length of the eye-piece lens

Parts of a compound microscope and functions

Head: It is located at the top portion of the microscope. It contains Eyepiece.

Eyepiece: It is also known as ocular, which is located at the top of a microscope. Viewers see the specimen through it.

Body Tube: It’s a long tube, which connects both eyepiece and objective lenses.

Nosepiece: Nosepiece is located at the bottom portion of the body tube. Objective lenses are remain attached to it. It can rotate to adjust the objective lens.

Objective lens: Compound microscopes contain different types of objective lens (10x, 40x, 100x). These are located below the nosepiece. These lenses are closest to the specimen.

Stage: The flat metal platform is located above the condenser and below the objective lens. The slide of the test specimen is placed over it.

Stage Clips: It is above the stage. It holds the slide.

Base: It supports all the components of the microscope.

Arm: It connects the body tube and base of the microscope.

Illuminator: An illuminator is the light source of compound microscopes. It is a low voltage bulb, which is located below the stage.

Aperture: It is a small hole in the middle of the stage. It passes the light from the Illuminator to the specimen slide.

Condenser: It is located below the stage. It gathers and focuses light from the illuminator onto the specimen being viewed.

Iris diaphragm: It adjusts the amount of light that reaches the specimen.

On/off switch: It is located at the base. This switch turns the illuminator off and on.

Stage Controller: These knobs move the stage in left and right or up and down.

Brightness Adjustment: It is located at the base. It adjusts the brightness of the Illuminator.

Diaphragm: It is a five-holed disk placed under the stage.

Uses of Compound microscope

1. Compound Microscopes used for blood analysis in pathological labs.

2. In forensic laboratories, compound microscopes are used for examining human cells, paper, etc. Which are related to the crime scene.

3. Used for the detection of drugs, by viewing their particles under compound microscopes.

4. In university and college laboratories students use compound microscopes for studying fungi, bacteria, plant cells, animal cells, etc.

Advantages of Compound Microscopes

1. It is not very expensive.

2. Can look at live samples

3. Can magnify up to 2000 times

4. This microscope is easy to use.

5. These microscopes are easily transferable due to their compact size.

6. It can produce a clear image as compared to a simple microscope.

Disadvantages Compound Microscope

1. Compound Microscopes Can’t magnify more than 2000 times