Light Microscope

The light microscope is a type of microscope in which visible light is used for illumination. The light source usually used in this type of microscope is an electrical lamp. The optical component of a light microscope consists of three types of glass lenses which are
Condenser
Objective
Ocular
 

microscope

 

Condenser function is to gather light and creates a beam of light which is focused at the level of the specimen to be observed.
 
As the light from the condenser passes through the specimen it enters one of the objective lenses. And there are four objective lenses available in the microscope which are fixed on a movable turret located just above the specimen.

The objective lens magnifies and projects the illuminated image of the specimen toward the ocular lens.
 
Ist objective lens magnifies image 4 times
The 2nd objective lens magnifies image 10 times
The 3rd objective lens magnifies image 40 time
The fourth objective lens is used with oil and therefore is also called an oil lens and it magnifies the image 100 times.
 
The ocular lens also is known as the eyepiece lens further magnifies the image 10 times and focuses the resulting image on the retina of viewers eye.

On the basis of the eyepiece lens, there are two types of a light microscope

1. Monocular microscope     It contains one eyepiece lens
2. Binocular microscope       It contains two eyepiece lenses
 
The maximum magnifying power of the light microscope is X1000 and resolution is 0.2 micrometer.

History of a light microscope

Jansen was the first scientist who invented a compound the light microscope in 1595. The microscope that was invented by Jansen has two lenses. One lens produces image and the second lens magnifying the image produced by the first lens. Jansen microscope has the ability to magnify an object nine times.

Leeuwenhoek in 1670 invented the simple microscope with one lens that has the ability to magnify an object 200 times and the resolution power is also high then the other microscope present at that time. The main reason that his microscope works better is that he crafted better lenses. Due to his amazing invention, he was the first person who sees individual cells, bacteria, protozoa, and sperm cells.

Robert Hooke modified the compound microscope by adding many features to it. The features that are added by Robert Hooke to the compound microscope are,
1.  Adding a stage that holds the specimen
2.  Illuminator
3.  Coarse
4.  Fine focus control.

Up to 1800, the microscopes that are invented by Jansen, Leeuwenhoek, and Robert Hooke has the ability to magnify up to a limited extent and the images formed show blurry edges.

To overcome these problems significant improvement occurs in the microscopes in the nineteenth century when Zeiss and Ernst added a substage condenser to microscopes and developed superior lenses.

Advantages of using a light microscope

The light microscope provides the ability to you to see colors in specimen while, on the other hand, another type of microscope known as an electron microscope produces only black and white images.

Light microscopes have the ability to magnify objects up to 1000 times.

With the help of light microscopes, you can see living specimens.

These types of microscopes can be bought easily with a very cheap price.

Light microscopes are also used in the various subdivisions of anatomy and physiology.

Disadvantages

The main disadvantage of Light microscopes has its limited ability of magnification and resolution. In light microscopy, you can not observe structures smaller than 0.275 microns. An object smaller than 0.275 microns are when studied with the help of a light microscope they appeared blurred and sometimes they are not visible.

To study smaller structures anatomists and physiologist’s uses electron microscopes that give more details.

Preparation of tissue for light microscopy

The direct microscope examination of the living cell is possible only to a limited extent. Mostly dead tissues are used for the microscopy which immediately after the removal from the body is treated with chemical preservatives and then cut into thin slices.

These thin slices are known as histological sections.

These histological sections are then stained with various dyes and now can be studied with the microscope in the transmitted light.

Preparation of tissues for microscopy involves four major steps which are

1. Fixation

The purpose of fixation is to preserve the cell or tissue with the least possible alteration. This goal is achieved by using chemical compounds which are known as fixatives.
 
Fixatives bring stabilization of the proteins. The most commonly used fixative is formalin.
 
Pure Formalin consists of 37% formaldehyde in water.

2.Embedding

After fixation, the cells or tissues need to be sectioned but these are very soft and cannot be sectioned. therefore we embed the tissue in a material which after hardening has a consistency that permits it to be sectioned together with the tissue piece.
 
Paraffin is the most used embedding agent.

3.Sectioning

Sectioning is the cutting of tissues into thin pieces and it is carried out with the help of a machine known as a microtome. These sections are then mounted on a glass slide.
 
Sections are usually 3 to 10 micrometers thick.

4. Staining

Most of the body tissues are colorless and it is difficult to study their structures. To overcome this problem we stained the sections with various dyes and these dyes give a characteristic look to it.
 
Stains are neutral salts which contain both acidic and basic radicals.

See the structure of the plasma membrane

summary

A light microscope is a type of microscope in which visible light is used for illumination. The optical components of the light microscope are a condenser, an objective lens, and an ocular lens. The condenser gathers the light and projects it toward the objective lens. the objective lens then projects the illuminated object toward the ocular lens that then further magnifies the image. The ocular lens is also known as the eyepiece lens. On the basis of eyepiece lenses, there are two types of light microscopes that are monocular microscopes and binocular microscopes. monocular contains one eyepiece lens while the binocular microscope contains two eyepiece lenses. The first compound light microscope was discovered by Jansen in 1905.