Have you ever wondered how a light microscope works? How does it magnify a specimen that we cannot even see with our naked eyes? Well, here’s a complete guide to tell you all about working with a light microscope.
Light microscopes, just like stereo and compound microscopes, are the most used microscope types. You will find them in every school, hospital, research center, etc. They use light and a number of lenses to magnify objects.
If you own a microscope or are planning to have one, you should know how to use it, and it works as this will help you yield maximum advantages from your microscope.
The more you know, the better you can use it.
Table of Contents
The Principle behind How a Light Microscope Works?
A light microscope uses incident light and a sequence of lenses to create a magnified image. There are two lenses; an objective lens and an eyepiece.
The third type of lens, the condenser lens, focuses the light rays, and then the objective lens and eyepiece magnify the specimen.
Parts of a Light Microscope
To understand the light microscope’s working mechanism, it is essential to understand its parts and construction. It has structural parts for support and optical components for providing a magnified image.
The eyepiece, also known as an ocular lens, is present at the top of the body tube. Its magnification power is usually 10x but ranges from 5x to 30x.
The body has a lens tube with an eyepiece at the top and an objective revolver having four objective lenses at the bottom.
Objective lenses are four in number that you can switch easily. They are of 4x, 10x, 40x, and 100x magnification power. The lens with 100x objective power is also called an oil immersion lens.
It is the place where the slide to be observed is placed. The slide is held in place by the clips.
These are two condenser lenses present just before the diaphragm. They are essential for image clarity. They focus light rays onto the specimen through the aperture.
Fine and Coarse Adjustment Knobs
These knobs move the stage up and down to bring the specimen into focus.
The aperture is the hole in the stage through which light from the source reaches the specimen.
The diaphragm is present just beneath the stage. It controls the amount of light that reaches the specimen.
A light source illuminates the object. A light microscope may have a mirror that reflects incident light onto the specimen or a Light bulb, or it may come with an LED light source.
It provides stability to the microscope.
Light Microscope Working Mechanism
When we talk about the microscope working, there are two features that we need to consider.
- The Magnification
- The Resolution Power
The light microscope magnification measures how much a microscope can magnify an object. The better the magnification, the better the microscope is.
The total magnification of a microscope is obtained by multiplying the magnification power of objective lenses and the eyepiece. A light microscope usually has 40x to 100x magnification power.
The higher the magnification, the closer the lens is to the object. The maximum magnification of a light microscope should be up to 1500x because, beyond this, the clarity of the image is lost.
The resolution power of a light microscope is defined as the ability to distinguish between two points in a specimen. The resolution depends upon two features; the numerical aperture of the objective lens and the wavelength of light passing through.
The higher the numerical aperture of the objective lens, the greater the resolution. For a higher resolution power, the wavelength of light should be shorter.
Locating the Specimen
A light microscope uses a thinly sliced specimen placed on a slide. The slide is placed on the stage. To adjust the specimen, we use a Coarse Adjustment knob. The coarse adjustment knob adjusts the stage to bring the specimen in focus.
It adjusts the stage by either moving the stage up and down or moving the body tube. After adjusting the height of the specimen, the fine adjusting knob is used to bring the object into focus. This creates a sharp image.
The light source beneath the stage illuminates the object. The most recent microscopes have an LED light source. The previous ones have a mirror which focuses light from an external source.
The diaphragm is rotatable and has many holes of different sizes that determine the intensity and cone of light that reaches the object. The condenser lens focuses straight light waves on to the specimen.
After reaching the specimen, the light waves diverge and fall upon the objective lens. The diverging of the light makes the specimen look bigger on the objective lens. The objective lens forms an upside-down/inverted and a real image because it is close to the object.
The ocular lens or the eyepiece then further magnifies the image. It does so by diverging the light rays more, and an inverted, and a virtual image is formed. In other words, the ocular lens functions further to magnify the image created by the objective lens.
You can find different types of light microscopes, such as compound microscopes, at your nearest shop or on Amazon. They may have different specifications and may be used for different purposes but they work in the same manner.