OK, so does NV work sort of like NRTV in that a large OTA isn't really needed? I use my 80mm and sometimes my 152mm on those occasions when I want to do NRTV. Is there a cut off point of sorts where the view through a larger OTA is equal to the NV view? For instance, the detail I see of the above discussed Orion nebula with my 14" Edge or my 16" DOB combined with an O-III filter or the DGM MPB is stunning in detail.
I am sorry but I don't know what NRTV stands for. Something like Near Real Time View?
While you can use NV to image, when used at the eyepiece, the view is not "Near Real Time." it is real time. (Though you can image with it if you like as well, and get very good results with very short exposures, but not in color).
I look in and I see a view. There is no integration time or anything. If I move the scope, the view instantly changes and there is no straking or fading of the view. It behaves just like an eyepiece.
NV Is best used with faster instruments but typically, NV will give results on stars that is easily equivalent to doubling the aperture. A 6" scope used with NV will show stars of limiting magnitude that a 12" scope would be needed to show when using glass eyepieces. Some say more and they may be right but it depends on a lot of factors, so I tend to be conservative, but I have seen well over 2 magnitude gain many times, so doubling should be considered as a reasonable minimum expectation, but I have seen Mag 17.8 stars using my 12" dob from the city. In real time...
Galaxies will vary a bit, but in my own experience, I think a doubling of aperture is minimum. I can see very faint galaxies from my red zone that escaped me using any size telescope I had used prior to NV. Even my 6" shows more galaxies than I could get from my C14 under similar skies, and my 6" does better than the C14 did under Bortle 5. Some of that though is because my 6" is f/2.8. NV Devices work best with fast instruments. With an 80mm f/6 refractor though, under Bortle 2 skies, I had fields of view that had many galaxies in view at the same time. Crazy. Oh, the galaxies were tiny tiny tiny at 20x, but still resolvable as galaxies.
I can see the Whirlpool with comanion and with spiral arms in real time from my red zone sky. Takes a pretty clear and dry night to see it well, but that is not a specific to NV condition. It happens with cameras and with regular eyepieces. Some nights are worse than others, some better.
Using Peter's 16" f/4.5, we have seen dark lanes in the Rosette from Bortel 5 skies. So, no limit on the size scope you can use them in.
On nebula, the difference is profound. I doubt that it would be easy to see some of the nebula I can see from the city even using all but the largest amateur scopes under very dark skies.
Did you know that M29 is inside of a nebula? I can this nebula on a good, clear night from my Red zone sky. I can see that in real time.
The Pillars of Creation in the Eagle Nebula? I can see that in my 12" Dob from my red zone skies.. I can see it in real time. Is there some noise? Yes. Does it bother me? Well, I was so excited the first time that I saw the Pillars of Creation, I have to tell you that it was one of the great moments of the 35 years I have been observing, and I did not even think about the noise.
I see nebula all over the sky. At 1x, under dark skies, the amount of giant nebula is unreal. There are nebula out there so big that they are hardly ever imaged by amateurs.
Reflection nebula do not show well in NV. Too blue.
And of course, you don't see star colors or the color visible in some planetary nebula.
As has been pointed out by others in the past though, NV is not an either/or propostion. Because it can be used exactly like an eyepiece, if you want to see color, do what you do when using conventional eyepieces, which is simply to swap it out. If you think the view of a double star would be better in a glass eyepiece, you pull the NV device out and put in another eyepiece! It is not mutually exclusive. Using NV is just like using any other eyepiece. If it is not the right eyepiece for the subject, you simply change eyepieces!
Still, it is not for everyone. When running heavy filters on faint nebula, the view can be noisy, but you can see things that you would not otherwise see, and you can see them in real time.
It is the real time aspect of it that most appeals to me. It is just an eyepiece, but one that greatly enhances the performance of a telescope.
Faster scopes work better than slower scopes, but with afocal projection, you can turn an f/15 scope into an f/7.5 scope just by using a 55mm Plossl. A 12" f/5 scope would become a 12" f/2.5 scope using afocal projection with a 55mm Plossl (and I don't know why EAA people are not using afocal projection more. It might work better than using focal reducers in some cases). Now I don't usually use afocal, preferring to work at prime focus, but I can use it if I like because it does not take any expensive special equipment (other than the NV device of course).