Calculating magnification

[trj]

How can I work out how much magnification I'm using? I read advice about viewing conditions being suitable for "x100" or "x300", but am unsure how magnified my view is.

I'm using a 10mm eyepiece with an 220mm reflector. The telescope is about 1320mm long in total, I'm not sure of the focal length, I'd guess ~1200mm

The moon fills about 3/4 of my view.

Is my magnification 1200/10 = x120 ?

The moon is half a degree across and my field of vision were 60 degrees, this would seem to fit.

[Stu]

That's correct, magnification is:

Focal length of scope/Focal length of eyepiece.

Actual field of view is:

Apparent field of view of eyepiece/magnification

Hope that helps

Stu

[JamesF]

Which means that if you could find two stars that you could just see at opposite edges of the field of view of the eyepiece and you knew the angle between them you could work backwards to find the magnification and then to the focal length...

James