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IMO the QE difference alone is a killer. If a OSC has a third of the QE then you must expose 3 times longer for the same flux and still you have a worse S/N ratio (3 times the dark noise). This wouldnt matter so much on bright objects though, and carefull dark subtraction.
Ive never seen an explanation why the QE is so low on OSCs. An external filter on a mono has a pass of some 95% or higher at the filtered frequency so dosent affect QE much of the sensor, but the OSCs on-chip filters seem to dump the QE, is the filter "film" or whatever much less efficient on a OSC?, I guess so, must be.
The res difference is something I puzzle about too. OK one quarter of the pixels are used for each colour (approx) on a OSC, but it seems to me, the interpolation is pretty good and its acurracy would be better than seeing at long FLs anyway, so your sort of getting extra exposure for free, albiet a carefully crafted processing trick. Im hard pressed to tell the res difference between a colour and mono small-pixel sensor final RGB pic for the average longish FL pic, despite the experts banging on about the theoretical difference.
NB is just woefull on a OSC, as you would expect, with the internal filter and then another filter at a different frequency after that. You would have to really not be interested in NB long term if you had a OSC, or put up with insane effort for the odd excursion. Bang goes the "easier" moniker right there, for NB.
I mainly do NB or HaRGB, because in urban skies LRGB is very limiting and requires no moon and far more exposure time for a given result to overcome skyglow (again, bang goes "easier").
Ive sometimes been tempted by a OSC, but ONLY for possible feild use in no moon dark skies, for which indeed, OSC capture is easier on brighter objects.
For urban skies, a OSC limits use to low QE LRGB and the difficulties that come with that without, realistically, the option of superior NB S/N performance, HaRGB at least is becoming more and more popular.
A motorised filterwheel makes the capture difficulty the same as a OSC IMO, and the extra processing required for seperate filter subs is so simple and automatic, that the extra work compared to the hrs spent in PS, is trivial. You can take RGB rotating sequences to assure a result if the weather turns bad.
So, in short, if you want a simple mobile dark sky rig for bright LRGB, the OSC is the go. For everything else, monos the answer.
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