Dear All,
I am lucky enough to own a Bushnell Northstar 4.5" GOTO reflector which (of course) beats-as-it-sweeps-as-it-cleans!
My question (only 1) is what is its real focal length. It is described as 900mm long (honest you can check), and its magnification maximum theoretical as being x675 with a 4mm SR and a X3 Barlow. The calculations work out (900/(4/3))=675. and the scope would be a 900/114=f8 ratio. relatively long.
The trouble is the scope itself is umm only 880mm oa between the perpendiculars. The distance between the primary and secondary mirror is only about 700-750mm so really a f ratio of about f6.1. Is there some other part of the light path I should be including?
This matters in determining what eyepieces to buy and in the making of approximate practical magnification limits, and of course in exit pupil calculations.
If someone could set me right that would be great.
cheers