How do I figure the magnification on a telescope.?

I know if there is a single number with the ';X'; you multiply that by 35 to get the power but what if there is a number like 900mmx60mm? Does this mean the telescope is a zoom and will go 31500 to 2100? And if so is this a good number.How do I figure the magnification on a telescope.?
Lots of confusion, both in your question and in the answers!





Astronomers generally refer to magnification as 40x, 100x, etc., meaning that the telescope magnifies forty times, a hundred times, etc. Cheap telescope manufacturers confuse things with numbers like you quoted: ';900mmx60mm'; is something no astronomer would use...it probably means a telescope with 60 mm aperture and 900 mm focal length.





Magnification is calculated by dividing the focal length of the telescope (900 mm in the example you quoted) by the focal length of the eyepiece. So a 25 mm eyepiece yields 900/25 = 36x, and a 10 mm eyepiece yields 900/10 = 90x. I don't know where you got the number ';35'; from...I've never heard that in 50 years as an astronomer!





You won't get much of a telescope for $150 to $200. The least expensive telescope which I would recommend is the Orion StarBlast 4.5'; reflector at $180:


http://www.telescope.com/control/product鈥?/a>





However, in this price range, a very small increase in price will bring a big increase in quality:


http://www.telescope.com/control/categor鈥?/a>How do I figure the magnification on a telescope.?
Whilst Tom's answer is the accepted average magnification (50 times the aperture in inches) it is not the case with a good quality telescope in excellent seeing conditions.





I have a good quality 4 inch refractor, and in good seeing conditions can push it well past 80 times the aperture with no loss of image quality.





I would say that 50 times is a pretty poor telescope with average optics in very average conditions, nothing excellent about that.





As for getting a decent telescope for US$200, wou wont, it will be useless for astronomy. You will need to spend about US1,000 for just an average scope. Get a decent pair of binoculars first which falls into your budget. Celestron make some nice models.





Buy a telescope later when you can afford it and are familiar with the sky, otherwise you will be disappointed and frustrated. You need to know a lot about telescopes before any purchase should be made.
mag = focal length / eyepiece diameter





fl and eyepiece dia in centimeters
Don't go by the ';x'; number for magnification. Eyepice magnification divided by Focal length will give you the ';x'; number you are looking at an object at.





http://astronomyonline.org/Science/Teles鈥?/a>





Good basic article on magnification:





http://irwincur.tripod.com/magnification鈥?/a>
I don't know where you got that bit about multiplying by 35. You might be confusing that with finding the maximum practical magnification for a scope, which is roughly 50 or 60 times the scope's aperture in inches, or 2.4 times the aperture in millimetres.





Note that that's the maximum PRACTICAL mag for a scope with EXCELLENT optics, under conditions of BEST SEEING. It doesn't always apply.





To find the magnification with a certain eyepiece, as mentioned, divide the focal length of the scope by the focal length of the eyepiece..





The 900 X 60 means the focal length of the scope is 900mm and the aperture is 60mm. Any scope which is described in such a way is probably cheap rubbish.