Altair 8x50 guidescope focal length

[ebdons]

Hi all, not sure if this the correct forum section to ask this but just need some info on a 8X50 converted finderscope which I converted into a guidescope with clamp ring etc, the focal  length of the scope is similar to celestron 9x50 finder which is 180mm from end of front lens cover to rear body end not sure if the FL is 180mm or thereabouts, anybody on here have the calc that I can use to find out.