Having had an interest in trying a decent-sized refractor or Cat for quite some time, would either provide an observing advantage to my Newtonians?
Most likely not unless aperture is the same. Maks and apos do have better star tests, with much better looking stars and no diffraction spikes, but without resolution (aperture) it won't be enough to surpass a larger newtonian.
My F13 90mm Mak does blow away my 114mm F4 reflector when it comes to planetary performance, but their unobstructed apertures are very similar.
Also consider atmospheric seeing: On an average night, my 6" SCT provides I'd say ~65% of the planetary detail my 10" dob would on the same night, but there are rare spectacular nights of steady seeing when my 10" dob leaves the SCT in the dust.
Oh, I love my 16", it works well for everything. And yes I collimate and cool every outing. Just asking as I have really never used any other type but Newtonians, and I know different types have their finer points.
The "observing advantage" will revolve more around factors like (much) faster cooldown, much better ergonomics on your Bresser EQ mount (less need to keep rotating the newtonian tube to avoid uncomfortable eyepiece positions, fewer vibrations thanks to a shorter Mak/SCT tube), or a much wider FOV (in the case of an ED refractor), but still in terms of pure resolution and detail for planets, aperture rules.
That said, last saturday I noticed the sky was very clear, stars weren't twinkling as much. Mars was very high in the sky (20º from zenith, I'm at the equator), but I had to get up early next day. I didn't have much time (only 20 minutes). Still, I felt I wanted the resolution of my "big" 10" dob for Mars so I set it out, collimated it, gave it 10 minutes to cool down, and observed. 20 minutes total.
It was alright, but frankly, the Mars view I got 3 weeks ago with my 90mm Mak was better. Of course, for longer sessions, with enough cooling time the 10" dob leaves the 90m mak in the dust, but for very quick sessions, when thermals come into play, the C90 has already showed me the martian polar cap and hellas by the time I'd barely be finished setting up and collimating the dob. My C6 strikes a middle balance with somewhat quick thermals, more resolution than the Mak, and splendid ergonomics.
Optics are not everything. If you only consider the optics then you'll always arrive at the conclusion that aperture is king and you want the most possible for the budget, which means a dob.
But then again, optics are not everything. Thermals, ergonomics, time shortage (either because clouds will carpet the sky 40 minutes after dusk, or because I have to work next day), setup complexity, vibrations, health (my bad back) and portability, do matter as well, all this while atmospheric seeing limits what larger optics can do.
Final note: You found your ST80 not to be an exceptional best observing tool. Indeed it is not, but when I had a chance to vacation on a bortle 2 remote beach with sight of the south pole, I was so glad I could pack the little thing in my luggage. My best sights to date of Carina nebula, Andromeda, the Southern Pleiades, the Jewel Box, NGC3532 and the double cluster. I'd rather use that little scope from a bortle 0 sky than my 10" dob from my city home (bortle 8)
Edited by Adun, 22 August 2018 - 03:36 PM.