focal length

Hello everyone!
I am planing to build a 14 inch newtonian telescope in the summer but there is questions I am having problems with, I have never built a scope before.

I am buying the mirror which will be a 355mm(14 inch)with a focal lenght of either 1778 or 1473mm (f5 or f4.1).

What I need to know is how far apart the mirrors need to be,is it the focal lenght or what?And how much bigger should the internial diameter than the mirror :S

The answer depends on a lot of assumptions--like how high the focuser is, what size diagonal, and all sorts of stuff.

Go here

http://home.att.net/~dale.keller/atm/newtonians/newtsoft/newtsoft.htm

and download the program. Then make some assumptions and re run till you get a design you are happy with.

Alex