Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: slymanuk on 28/05/2004 10:47:53

Title: Telescope normal adjustment and diagrams
Post by: slymanuk on 28/05/2004 10:47:53

Hi, I am a British 'A' level physics student and could use a little bit of help please:

In reference to an astronomical/refracting telescope...what does normal adjustment mean?
Is it when the distance between the two lenses is equal to the sum of the focal lengths?

Also, on ray diagrams of the reflecting telescopes....Do light rays travel to the mirrors, or the planes of each mirror?

Thank you for your time

Liam Singh

Title: Re: Telescope normal adjustment and diagrams
Post by: Dan B on 28/05/2004 18:10:37

Normal adjustment is when the distance between the objective and the eyepiece is equal to their focal lengths added together.

A good starting point for a better explaination:

Chris Kitchen: Telescopes and Techniques. Springer-Praxis

I don't quite understand the ray diagram question.... However, in a reflector light will travel parrallel to the optical aixs until it hits the mirror, it will then bounce towards to (prime) focal point of that mirror. However, there will normally be another secondary mirror to rebound the light yet again to the cassegrain focus.... I could go on for hours, but won't.[:D]

Title: Re: Telescope normal adjustment and diagrams
Post by: gsmollin on 30/05/2004 00:31:56

In a reflecting telescope, the mirrors are front surface mirrors, and are normally coated with aluminum. The light rays travel until they strike the aluminum surface, then are reflected. The glass of the mirror is not part of the optical path, and serves only to carry the aluminum coating.