I've been comparing three of my binoculars (Apogee 25x100, Garrett 30x100, Garrett 28x110) to my Celestron Omni XLT 150R f/5 150mm refractor with a supercharged Baader MkV binoviewer over a few clear nights. My purpose in doing this is to try and possibly get rid of a few of my binos, and replace them with an adjustable power, tracked platform (scope on an EQ mount w/drives), with angled viewing instead of straight thru.
I think we can mostly agree that 90 degrees is better than 0 degrees for most objects above 20 degrees or so in the sky. I've also found that, to me, telescope eyepieces are more comfy (more eye relief mainly), tend to fog less quickly, and provide sharper views as compared to most built in eyepieces on binoculars.
My correctors for the binoviewer include a Baader 1.25x GPC used with the 32mm T2 prism diagonal, and a Siebert 38mm clear aperture 1.0x (0.93x according to their website) used with a 99% reflectivity diagonal (this makes an observable difference in brightness as compared to a generic 2" diagonal that I have); I purchased the Siebert as it has 38mm of clear aperture vs. the 24.5mm of clear aperture that the Baader GPC has, and because it will put the focus out farther as my 35mm Ultrascopics run almost right up to the stop to reach infinity. The Siebert OCA does indeed gives you around an extra 2" of outward focus.
I mainly viewed the Double Cluster and the Orion Nebula for comparisons. Assuming no losses or aperture constrictions, the 150mm refractor should give me the equivalent of a 106mm binocular. FWIW, I've flashlight tested the clear aperture on my 25x100 to be 93mm, the 30x100 to be right at 100, and the 28x110 to be 108.5mm.
Scope w/binoviewer in configurations that provide near these binocular magnifications:
Meade 25mm HD-60s (~28x) and APM 24mm UFFs (~29x) with the Siebert 0.93x OCA & 99% diagonal
35mm Ultrascopics (~27x) & 32mm TPO Plossls (~29x) with the Baader 1.25x GPC, using the Baader 32mm T2 prism diagonal
28x110 - brighter than any of the scope configs, more stars seen in the Double Cluster, better contrast on the filaments in the Orion Nebula; it's really striking at how much brighter the entire FOV is when you change between the scope/BV and these binos
30x100 - pretty much equal, really hard to discern a difference; this was not the case until I swapped the generic diagonal for the 99% reflectivity one
25x100 - bino provides a slightly brighter view (~23x bino vs. ~27x scope/BV)
Putting the 35mm Ultrascopics in with the Siebert OCA gives a very nice view of ~20X and about 2.46 degrees; this view is on par with the overall brightness from the 25x100. The brightest low power view seems to come from using the Baader 1.25x GPC setup with the 35mm Ultrascopics (~27x); this view seems brighter than the view with the 35mm Ultrascopics and the Siebert, but still noticeably short of the brightness of the 28x110.
The single eyed view with only a diagonal (no binoviewer) and the Meade 25mm HD-60, for 30x, appears to be at the same level of brightness as the 28x110 using both eyes, but sharper. The sky is immediately brighter in the scope with the single eyed view, and more stars are discernible in the Double Cluster as compared to the binoviewed view.
FWIW, the 25mm Meade HD-60s seem to be just a smidgen brighter than the APM 24mm UFFs; I'm not sure that ~1x change in magnification can account for that, but it's easier to see a few faint stars with direct vision in the Double Cluster with the Meades as compared to the APMs.
The stars do focus down to pinpoints much better in the scope w/BV, providing a much sharper view over pretty much the entire FOV, and there appears to be less chromatic aberration with the scope even though it's an f/5. The stars in the binos, especially the 28x110, focus well, but the brighter stars appear larger/more bloated. None of the binos are sharp to the edge, with the sharpness beginning to noticeably fall off 50% or so out.
I'm now leaning towards a bino chair/zero gravity chair on a swivel base with the 28x110 mounted in front of me and to the chair. Or maybe giving my 800mm f/3.9 newt a go with the Siebert OCA.
So, there you have it, minor report but maybe helpful to someone out there.
Edited by aa5te, 13 January 2021 - 06:12 PM.