Er, can I butt in here? I'm kind of the cause of Roger's headache
and while I can see people trying very hard to be helpful it's getting a bit off track of what we really want to know.
We really want to know about star brightnesses, not nebulae. We're not trying to photograph deep sky objects, it's all to do with an upcoming Pluto occultation event on 4th June. The target star is around mag 15, and the argument is whether an 8" is enough aperture to pick up this star using a focal reducer and my gstar camera. On one hand I've been told it's ok, on the other that I should try to get to a bigger scope.
I do understand that the wider field and faster f/ratio will lead to the stars being more pinpoint and hence brighter - but will they still be bright enough in this case?
(I do have an ulterior motive to all this, I'd love to know how to work out what combo of scope - f/ratio-camera etc is needed for certain magnitude limits in this kind of situation. Yeah, I know, I should be asking davegee, but Roger has started this thread first, so why not try...)