PS Surfer wrote in
m:

On my daily walk with my daughter, my thoughts began to wander
thinking about building another scope, but the following riddle, so to
speak, came to mind. Given two hypothetical scopes, say one 8"
diameter, 750mm Focal length (scope A),

Scope A Focal Ratio = 750/203 = 3.7

Most eyepieces will not work well with such a fast scope. If the scope is
a Newtonian it will also have severe coma.


and a 6" diameter 1500mm focal length (Scope B).

Scope B Focal Ratio = 1500/152 = 9.9


If you are talking Newtonian, then this scope will have negligable coma
and will work well with any eyepiece design.


If you take an 4mm focal length eyepiece and place
it on scope A, and focus in on say Saturn, then an 8mm focal length
eyepiece on scope B and focus in also on Saturn. Given that both of
these scopes have equal magnification, and otherwise we will assume
them to be of equal quality, and design, which would be the better
setup?


Scope B. Your scope A is just too fast to work well with most eyepieces.

Llanzlan.