>>2640752They're about equally important, and all telescope manufacturers will list the focal length alongside the other two specs. For casual use, however, it's redundant. Diameter x F-number = Focal length. The formula is easy enough for astrophotographers, who are already a very technical bunch, to understand the ratio implicitly. Among telescopes of the same diameter, faster aperture = shorter focal length. Among telescopes of the same f-number, larger diameter = longer focal length.
Also, it's not like there's a huge difference among telescopes. You're talking about the difference between 2000mm and 2500mm. Both can resolve Andromeda and Pluto just fine. It only really matters when you're getting into exotic superfast refractors, but those cost like ten grand and you already know what you're getting into.
