Are you adjusting for the magnitude of the stars? And this thread is explicitly about a 4 inch refractor and an 8 inch Dob as per the moderator. In my experience an 8 inch F/6 Dob shows tight stars.
Both my 6" F8 & 8" F6 Newtonians have outstanding mirrors, but neither can present stars as the micro-dots I see in my 4" refractors, when all 3 scopes are at the same magnification -- say 30x (typical low power for me). That's one advantage refractors have over reflectors. Yes, I can split tight doubles with my Newts, but those individual stars won't be as tiny as in a refractor at the same magnification.
To be 100% fair (same apertures), stars in my 6" F8 ED were always smaller than in my 6" F8 Newt with both at the same magnifications.
Which one gives you the best views in your opinion: a good 8" dobsonian with premium optics or a 4" apo refractor? I never owned a newtonian so, to me, the answer is not so obvious.
Not picking on you OP, but why is it that most of these topics have the refractor at 1/2 the aperture of the reflector?
My APM 152ED was 3/4 the aperture of my Meade 826, and it routinely out-performed the Newtonian. Neither scope is top-tier -- well-made mid-tier, IMO. 30+ years ago, my hand-made D&G 5" F10 refractor showed more planetary detail than the 8" Newts at star parties. So, OP, you'd need at least a 5" refractor to tie / beat an 8" Newtonian on most objects -- though it would have to be an Outstanding 5" frac.
I sold my APM 152ED. I'm keeping my 2 Newtonians -- and my 4" refractors. Most nights, and most views, my 6" F8 Newt is like a 4" APO; and, my 8" F6 Newt is like a 6" APO. Last night, in 8 / 10 seeing, my RV-6 was sharp on Mars & Saturn at 300x -- though I did back off to 240x for comfort. So much detail on Mars, and at least 6 colors on Saturn. Titan + 3 smaller moons. I paid just $150 for this complete 1971 Classic kit (scope + EQ + 6 eyepieces & Barlow - all original). I paid $600 for just the AT102ED OTA.
I know, reflectors almost always win the aperture per dollar argument. But they can also win the performance comparisons -- just took me 4 decades to figure that out...
Edited by Bomber Bob, 24 October 2020 - 04:33 PM.