Hello again, I have used both apertures extensively, so I've done my homework. 0.4 magnitudes, is the difference between detecting an object at the limit of detection in the 10", to seeing the object with averted vision with the 12" scope.
Under dark skies, this would be more noticeable, however it is not a big improvement, and even seeing a very faint 15.5v magnitude or slightly fainter star in the 10" would be detectable 50% of the time in the 10", and detectable with the 12" scope 75% of the time when used at the same power, under the same conditions.
When you increase the power in both scopes, fainter stars will be easier to see, and a star right at the limit of both scopes like stated above would have a similar effect, although the star being scrutinized will be slightly easier in the 12" scope allowing the observer to detect the star 25% longer then the 10" scope, at any given time.
If you really want to brighten up a 15v magnitude star you will need at least a 22" or bigger scope. Even in this aperture the true limit is usually not reached because of seeing conditions, and other factors, such as collimation, although 15v magnitude or fainter is rather routine in this aperture.
This is how it works, sense the eye does not see this change in a linear way, the object perceived in both scopes, will have a similar visual response. Yes the 12" will be brighter, but only a smidge brighter.
In situations like this it is really to close to call, to choose between a 10" or a 12" scope. I have both, so it doesn't matter. I have compared them both on the same objects, and the difference is there, but you have to look for it.
The jump from an 8" to a 10" is more noticeable on all objects, while the small jump in brightness from a 10" scope to a 12" scope is not enough to really discount the 10" by any means, so either one would satisfy. For galaxies you need to subtract 2 magnitudes from the stellar limit, depending on the surface brightness of the object.
Deep sky objects like globular clusters will be a smidge more crisp in the 12", and smaller objects like planetary nebula will have a smidge more color and luster, but not much more.
The Ultimate Test: I will see if I can get a glimpse of the extremely faint globular cluster, NGC 6749 in Aquila on the next dark, and clear moonless night through both scopes, to test the two aperture's visual power...clear skies...
Edited by dragonstar4565, 27 July 2021 - 07:49 PM.