Lenses in Telescopes

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  • Created by: Zoeee
  • Created on: 03-05-13 20:09

Focal Length

To find the focal length of a converging lense:

Put an image of a distant object on a screen and measure the distance between the lens and the focused image. It works as the rays of light from the object are parallel and convere at the focal point.

The image is inverted, diminished and real, meaning it can be projected on a screen. 

A converging lens can produce magnified and diminished images depending on the position of the object.

When the distance between object and lens is bigger than 2f (focal length) it will be red text

 If the distance is between f and 2f it will be inverted, diminished and magnified.

When object is closer to lens than f, the image is virtual (can't be projected on screen), upright and magnified

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- Early telescopes had converging lenses at the front and diverging as the eyepiece. 

- Lenses have different focal points for different colours of light, making the image blurred.

A clearer image is formed by using a concave mirror instead of converging lenses. 

-In a modern refracting telescopes is all a coverging lense

- Reflecting telescopes are large but easy to move than a refracting telescope as the mirror has a smaller mass

A simple reflecting telescope uses a large concave mirror, a plane mirror and a converging lens

The concave mirror forms an image of a distant object, which is reflected towards the eyepiece using the plane mirror. 

- Modern telescopes can be placed in observatories in high areas, away from pollution. The air is cooler so there is less interference from the atmosphere. The Hubble Space telescope produces images of space by using infrared and ultraviolet waves.

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