f ratings on scopes

Dave · Guest

I see scopes with f/4 to f/10. What should I be looking for? Why does it matter?

Thanks

Dave

Jne_K · Site Admin Joined: 24 Sep 2003 Posts: 5400

Hi

f/4 is focal ratio - the ratio of telescope focal length to telescope aperture (size of the mirror or lens). For instance, a telescope with a focal length of 800mm and an aperture of 200mm (8") will have a focal ratio of f/4 (800mm divided by 200mm)

If you are a beginner, focal ratio and focal length are not features you need to focus on just yet. These features are involved with potential magnification and the physical size of the telescope and are more critical for astrophotography purposes.

The primary features a beginner should concentrate on in a telescope are aperture (size of lens or mirror), telescope design (reflector, refractor and so on) and type of mount.

For the basics and how to choose a telescope, see my article
How to choose the right telescope
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Guest · Posted: Tue Nov 13, 2007 10:08 am Post subject:

Thank You!

Jne_K · Site Admin Joined: 24 Sep 2003 Posts: 5400

You are very welcome and always great to see more folks getting into astronomy. Enjoy.
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