This maybe be a dumb question that I may answer in the question.
Typically we use fast glass or as fast as we can afford. In my case f7.5
In "Normal photography" if you take a long exp with lights at the largest aperture you have typically ie 4.5-5.6 or faster you wont get pointed lights without a filter. But if you stop down to f10 or less you get points without a filter.
So some astrophotos I see have pointed stars and some don't. Some have a mix
Now since we can't change apertures like on a camera and f7.5 is open enough to not get points and I doubt anyone puts a star filter on. My question is. What's going on?
hmmm f7.5 is without eyepiece. adding eyepiece stops down by a factor determined by magnification of attached eyepiece?
Which brings me to an f number 10-?
Am I on the right trail?
Just found this handy calculator
http://www.stargazing.net/naa/scopemath.htm