We can break down the word microscope. It includes the word micro, which means small and the word scope, which means to look at something carefully. So a microscope is an instrument we use to magnify small objects.

We typically want to see small things that can not be seen with the naked eye. For example:

  • Bacteria
  • Fungi
  • Microscopic animals (for example dust mites)

The Light Microscope

In a light microscope, a series of lenses is used to produce a magnified image of an object.

1. Object is placed on a rectangular glass slide.

2. The slide is placed on a stage with a light source below.

3. Light shines through the object and into the objective lens.

4. Light passes through the eyepiece lens and from there into the eye.

Making slides

If you want to look at cells under a microscope, spread a very small sample of cells on a glass slide. Then add a few drops of dye, which stains the cells. After this, place a cover on top of the slide, so that the sample can be viewed.


The focusing knobs are used to focus the image. The safest way to do this is by using the knobs to move the stage downwards, rather than upwards. When you focus upwards, there is a chance of the objective lens and slide colliding.

Microscopes have three or four objective lenses on a turret that can be turned. It is best to start off with the objective lens with the lowest magnification, which is usually x4. The x4 objective lens has the lowest magnification, so it has the largest field of view. This allows you to see more of the sample and it allows you to observe which part of the sample you want to observe.

Calculating the magnification of a microscope

To work out the total magnification of each lens, the equation is:

So, if the eyepiece magnification is ×10 and the objective lens magnification is ×60, then the total magnification is:

10 × 60 = ×600