Brendan, didn't you get any instructions/specs at all with the t'scope? To find the fl of your t'scope, divide the length by the diam. in inches. eg; 48" tube div. by 6" = f8. or if you're metric, 1220 div by 150mm = f8.1.
As Ken, and others have said before, ask and you will receive. We will help if able to.
Just the facts m'am.