Seeing further - DIY telescope

22 February 2009



Magnifying glassA magnifying  glassHand LensA handlens or another magnifying glass with a much higher magnification.


Hold the handlens close to your eye, and then hold the magnifying glass in front of it.

Slowly move the magnifying glass away from your face until you see an in focus image.


You should find that the pair of lenses produce a magnified but upside down image.


If you hold a piece of paper behind a magnifying glass, then the magnifying glass will focus the light from the scene into an image on the paper. This is called a camera obscura and is the basis of how your eyes and all cameras work. (
Find out more )

A camera obscura

If you used greaseproof paper as the screen you could use another high magnification magnifying glass to magnify the image on the paper you would see an inverted magnified image of the scene.

Camera Obscura with lens

In fact the light leaves the piece of paper in exactly the same way as it leaves the focus when you remove the paper, so it works even better if you take the paper away, and you have a telescope.

A telescope

This is a Keplarian telescope, and is probably the most simple type of telescope to build, but there are a huge variety of other types with various advantages and disadvantages.

We spoke to Dr Carolin Crawford, from Cambridge University, about how this telescope compares to historical, and modern telescopes. 
You can listen to, or read her response here.


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