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How does a microscope work and how to use one

What is a microscope? 

A microscope is an instrument that allows you to see something that is very small, sometimes invisible to the eye. The part of the microscope that makes this possible is the lens. 

What is a lens?

A lens in a microscope is a convex lens and looks like a flattened ball. It is transparent so light will go through it. The lens is usually made from glass or plastic and when the light is bent when it travels through the lens. The rounder, or fatter the lens is, the more it can make something look bigger. 

 The other type is called ‘concave’ and the edges are thicker than the middle. 

The simplest convex lens is a droplet of water

A simple microscope

The simplest microscope uses just one lens. The simplest lens is a droplet of water. The next simplest is a magnifying glass. People began to see things using lenses made of water over 600 years ago but no-one really knows who invented the first microscope. In 1670, a man from Holland, Antony van Leeuwenhoek, made an amazing lens himself by polishing glass until it was almost spherical. Using this he got a magnification of up to about x 300 and the invisible world opened up. This is what his microscope looked like.

A Compound microscope

A compound microscope usually has two lenses. One lens is in the eye piece and the other is the one that can be moved up and down. In some microscopes, this lens can be changed and there is a choice of magnification. To work out the final magnification, multiply the magnification of the two lenses together. For instance if you use two x2 lenses, the final magnification will be 2×2 or 4. Using a x2 and a x5 will give a final magnification of x10, or 10 times bigger. 

Use one eye or two?   Monocular or binocular( stereo)

If there is one eye piece, the microscope is monocular. If there are two eye pieces, it is binocular. It is sometimes easier to see if you are able to look with both eyes. It is also possible to attach a phone camera to one eye piece whilst you look through the other  one. If the image comes up onto a computer screen then you have a digital microscope. 

There are three things to get right to see clearly in a microscope: Focus, Lighting and Magnification

Focus

When an object is in focus, you can see it clearly and distinctly. There are two lenses in the microscope, the one nearest the eye is fixed and the lens nearest the object that we are looking at can move up and down. 

The lens nearest the eye is called the ‘eye piece lens’. 

The lens nearest the object is called ‘the objective lens’ .

To get a clear focus, the objective lens must be moved up and down until it is in exactly the right placed you can see the object clearly.

Lighting

Lighting can be done in three ways: 

Best from above 

To look at something like a dead moth, because the moth is quite thick and does not let light shine through it, it is best looked at with light shining on it from above. If light is shone from below, it looks like a black shadow outline. 

Best from below

To look at something that is very thin and transparent (lets light through), like a dead fly’s wing, use the lighting from below. 

Natural light

Sometimes using just natural light shows up different things on the moth.

 It’s always worth looking at your image all three lighting ways, then choose what’s best.   

Magnification 

How much bigger an object looks is called the magnification. The lens magnifies the object. If the real size of an object is described as ‘one’, and magnification makes the object twice as big, this is called ‘times two’, or x2. Magnification can be up to x1000 and more. A good magnification for looking at nature and micro plastic fibres is around forty times bigger, x40. 

Now Set up your microscope

This is a binocular microscope . The eye piece lens has x 10 magnification. There are 2  objective lenses. One is x2 and if this is used, the final image will be x 20. The other objective lens is x 4. This will give a final image of x40. 

  1. Find something to look at, here the example is a dead moth.
  2. Put it on the stage, in the centre.
  3. Look through the eye pieces, using both eyes. The eye pieces can move together and apart. Make the distance between the eye pieces comfortable for your eyes and when you can see clearly without lots of shadows.
  4. Focus
  5. Move the knob which moves the objective lens up and down until the moth comes into focus. That is you can see it clearly. If the objective lens is then changed, the image will need to be focused again. 
  6. People will have to change the focus so that the image is clear for their eyes.  
  7. Lighting
  8. Get the lighting right. This microscope has in built lights. Turn on the main switch. Then in turn turn on the switches for above lighting, then below lighting. What do you see? In this case the best image is when the above lighting is used. 
  9. Shining light from above gives a good view of the detail on the moth.
  10. 10.When shining light from below,  the image is a silhouette of the moth, because the moth is too thick to allow light from below to penetrate it. 
  11. 11.Without any extra lighting, in natural light, some detail can be seen.
  12. 12.Magnification
  13. 13.Use the x2 objective lens first. This, with the eye lens at x10 gives x20 magnification.
  14. 14.Move the objective lens up and down until the moth comes into focus.
  15. 15.Turn the objective lens mounting and bring the x4 lens into action.
  16. 16.Refocus and look at the moth at x40 magnification. 

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