Hello all, I am wondering if anyone would explain some basics about telescopes to me. I have done searches of previous posts and could not see anything that answered my question. I am wondering if anyone can explain the following relationships too me?

 

I have the fact that the following equations:

 

focal length = focal ratio * aperture

 

for a Newtonian reflecting telescope. Is focal length the ration between the light reflecting off the primmary mirror and the secoundary mirror?

 

How does the focal length of the eyepiece of the eye piece differ to that described above?

 

I realise the shape of the secoundary mirror must be a eclipse as its the cross section of a cone. However how does the major axis of this eclispe relate to the internal angles of reflection and focal lengths in the telescope?

 

Any help would be greaterly appreciated and further my understanding of physics greater!

 

Desperate physics student.

Try this

http://hypertextbook.com/facts/2002/JenniferHu.shtml

obtained with a google search for "astronomical telescope" basic reflector

It includes this paragraph, which I think indirectly answers your question.

" Hubble's focal length - the distance between the main mirror and the point at which it focuses light - is 189 feet (nearly 58 meters), or about three times as long as the shuttle, but because the light is additionally reflected by a secondary mirror back through a hole in the main mirror, a long focus can be attained within the confines of telescope."

Try this

http://hypertextbook.com/facts/2002/JenniferHu.shtml

obtained with a google search for "astronomical telescope" basic reflector

It includes this paragraph' date=' which I think indirectly answers your question.

" Hubble's focal length - the distance between the main mirror and the point at which it focuses light - is 189 feet (nearly 58 meters), or about three times as long as the shuttle, but because the light is additionally reflected by a secondary mirror back through a hole in the main mirror, a long focus can be attained within the confines of telescope."[/quote']

Thank you very much.