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Re: What Is F/10 Mean?

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Posted by Jennifer Younker/">Jennifer Younker on February 8, 2000 21:58:40 UTC

: : : : : : I'm about to enter the world of amature astronomy and : : : : buy a new telescope. I'll probably start out in the : : : : low end of things. I've been looking at Meade's 8" : : : : LX10. I'm a little confused after looking at all of : : : : the different telescope specs. What is focal ratio? : : : : Does a larger focal ratio mean better?

: : : : Thanks

: : The f number or is the focal length of the mirror. For : : example it you purchase a 10" diameter mirror with an F5 : : focal length, the point at which the light collected by : : the mirror would be focused would be 50" from the mirror. : : Check out this web site: : : http://wwww.tiac.net/users/atm/baffle.html

: : Good seeing

: : The notation "f/10" is read "F Ten" and refers to : the "F number" of the optical system. The : definition of "F number" is the ratio of the : focal length to the diameter and is directly : proportional to magnification. A larger F number : telescope has a larger magnification, given the : same eye piece. For example, an f/10 telescope : with a 6" mirror would have a 60" focal length.

I know where the "f number" comes from. BUt who thought of calling it the "f" number. WHat does it stand for.

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