Building a Refracting Telescope

by Robin Riordan

Pictured below you see the parts of a simple refracting telescope. During this activity you will assemble the lenses to make your own 16 power telescope.

The larger “convex” lens is called the objective This is the lens responsible for gathering the light from the object to be viewed. The smaller lens is called the eyepiece or ocular. This lens is responsible for projecting the light from the objective lens into your eye. Use the circles and plastic caps for holding the lenses in place.


The diagram below shows how the refracting telescope works. The light from a distant object enters the objective lens. That light is bent and converges to a point called the focus. The distance between the objective lens and the focus is called the focal length.

The light then emerges from the focus and continues toward the eyepiece. But notice something. The light which was on the bottom is now on the top and the light that was on the top is now on the bottom. So, everything looks upside down or inverted.

Finally, the light reaches the eyepiece and is directed into the observer’s pupil.

The focal length of the telescope is long. So, in order for it to work you need to go outside and look at a distant object. Something very far away.



How It Works:


Notice that the image appears to be upside down. Can you explain this from the above diagram?

Is there anything you could do to make the image upright?