Re: ATM focal legnth ..?

["Bill Prewitt" <bprewitt@neo.rr.com>]

A web calculator for Sagitta, focal length, and radius of curvature is here:
http://www.atmsite.org/software/sagcalc/sagitta.html

Sagitta for an 8.75" f8 would be  0.068"       (between #50 and #51 drill)
Focal length would be 70"

sagitta = (diameter * diameter) / (8 * radius of curvature )
focal length = radius of curvature / 2

You can get  the rest of the equations by doing View Source on the page....
showing the Javascript.

              Bill Prewitt

My webpage of telescope making and caving
http://home.neo.rr.com/imaging


>
> what is the equasion for calculating sag.
> also how do i determine the focal legnth.
> i want to grind an 8.75 @ f 8