# Thread: help! if you buid a telescope with a focal length of 1.3 m, what focal length...

1. ## help! if you buid a telescope with a focal length of 1.3 m, what focal length...

...should the eyepiece have to..? give a magnification of 100 times?

help!! how do i answer this question?

2. Originally Posted by marykate
...should the eyepiece have to..? give a magnification of 100 times?
f(eyepiece.)= f(objective) / magnification = 1300 / 100 = 13 mm

M (magnification) = f(objective) / f(eyepiece.) = 1300 / 13 = 100 x

3. Originally Posted by marykate
...should the eyepiece have to..? give a magnification of 100 times?

help!! how do i answer this question?
Another homework/exam question? How did AT.net get onto the homework help short list?

4. MaryKate

The Sky and Telescope Web Site has an article about telescopes that explains not only how to calculate the power of a telescope but just abount any other thing about telescopes that you wish to know. The article is not written in technical language and is easily understood. Also in the article is an online telescope power calculator. Here is a link to the site. It is free to the public: SkyandTelescope.com - Choosing Your Equipment - How to Choose a Telescope