Light Microscope: Functions, Parts and How to Use It

A light microscope is a biological laboratory equipment, which uses visible light to detect and magnify very small objects.

A light microscope uses a lens to focus light on a specimen, magnifying it to produce an image. The specimen is usually placed close to a microscopic lens.

Microscopic magnification varies greatly depending on the type and number of lenses that make up the microscope. Depending also on the number of lenses, there are two types of microscope:

  • Simple light microscope: it has a low magnification because it uses a single lens.
  • Compound light microscope: has a higher magnification than a simple microscope because it uses at least two sets of lenses, an objective lens and an eyepiece.

Light Microscope Function

The function of the light microscope is based on its ability to focus a beam of light through a very small and transparent specimen, to produce an image.

The image is then passed through one or two lenses for magnification to view. The transparency of the specimen allows for easy and fast light penetration. Specimens can vary from bacteria to cells and other microbial particles.

The principle of a light microscope is to visualize an image by using the ability of the lens to bend light and focus it on the specimen is what makes up the image.

When a ray of light passes from one medium to another, it is bent at the interface causing refraction.

The bending of light is determined by its index of refraction, which is a measure of how much a substance slows down the speed of light. The direction and magnitude of the bending of light is determined by the refractive index of the two mediums that make up the interface.

Light Microscope Parts

light miscrocope parts
  • Ocular

The ocular lens is part of the optical system, which is directed at the user of the microscope. This is the part that has at least one or more lenses.

The function of the ocular lens on a microscope is to convert the enlarged real-middle image from the objective into an enlarged virtual-image. The size of the incoming light cone will be adjusted to the size of the human eye.

  • Body Tube

Body tube is part of the microscope that serves to accommodate the lens system that enlarges the specimen.

  • Objectives

Objective revolvers are used in microscopes with multiple objective lenses, which have different magnification factors. By rotating the revolver, you can select the lens with the desired level of magnification.

  • Arm

Arm is a holder connected to all components that function as a support for the microscope so that the microscope can be used properly.

  • Stage Clip

The stage clip acts as a holder for the object plate and ensures that it doesn’t fall out of place accidentally.

  • Microscope Stage / Cross Table

The microscope stage is the part that serves to place the object plate with a cover glass on it. By sliding the platen, you can select the part of the object you want to view.

Higher quality microscopes sometimes use a cross table as a table. This makes it possible to slide the object plate through the adjusting screw.

Cross table is a technical term which is a table construction that is mounted into a rail system. There is an adjustment screw, which can be used to move the table with great ease and precision.

The screw is equipped with a measuring scale, so you can easily find a specific point of the object again.

  • Condenser

Condenser serves to bind the rays from the light source, so that the light can be projected on the object. Thus, every part of the object will be illuminated at the same brightness level.

  • Diaphragm

The diaphragm usually consists of one or two lenses. These lenses fractionate the light and all the rays leave as parallel beams. Aspherical lenses ensure that no aberrations occur.

This will guarantee better image quality. The production cost of the diaphragm is more expensive than the normal lens. You can tell which microscope is better by looking at it from this diaphragm.

Another way to reflect light perfectly is to use an optical filter with a dielectric surface. Bragg mirror which is a kind of thin mirror with a refractive index that can be high and low.

This mirror allows for very high-quality light beam reflection, which makes the image sharper later on and proactively reduces lens error.

  • Fine Adjustment Knop & Coarse Adjustment Knop

With fine focus you can adjust the distance between the object and the objective, to achieve the required sharpness. Fine focus works by moving the lens smoothly.

Like fine focus, coarse focus also moves the stage to adjust the difference between the object and the objective. The function of the coarse focus is to capture the exact distance roughly and quickly. Optimal sharpness can be adjusted to finer roughness afterwards.

  • Light Source

Early microscopes used concave mirrors to reflect light on objects. Then, they used light bulbs. Most microscopes operate with an LED light. The job of the light source is to illuminate the object evenly.

  • Base

Base is the very bottom. Base serves to accommodate all parts of the light microscope.

How to Use a Light Microscope

To use a light microscope, you can follow the steps below carefully.

  • Start with a low lens and a clean slide. The microscope stage should be lowered as low as possible.
  • Center the slide so that the specimen is under the objective lens.
  • Use the coarse adjustment knob to get a general focus. Then slowly move up the stage until focus is achieved.
  • Use the fine adjustment knob to get clear focus.
  • Center the specimen on a low plane before moving it to a medium plane.
  • Switch the objective lens to medium and focus using a fine adjustment. If you can’t see the specimen at this point, return to the low plane and re-center.
  • Once you’ve focused and centered on the medium power, you can move it to even greater magnification.