The simple, but not very satisfying answer is that NV makes almost any telescope better, and it excels when viewing dim, or previously invisible objects. Here are some thoughts based on my use of a PVS-7 with various scopes and lenses. These observations are based on viewing under dark skies and may differ from others observations under urban skies.
It is commonly accepted that NV works better with faster scopes, and while this is true in general, and especially true if you need filters to reduce light pollution, I find that NV also works well at higher f ratios. I have used mine at f25, but in general I stop at f15.
One of the handiest and most enjoyable scopes is one I cobbled from a 50mm sighter scope off an old Meade SCT. The focal length is somewhere between 200 and 300mm, which is nearly ideal for scanning the sky and observing large nebula. The best part is that it weighs so little.
I have tried various camera lenses (Canon FD). All give good views, but are heavy. My favorite is a 200mm with 1/4x20 tripod mount ring. The disadvantage is that these lens wont focus using a 45 or 90 degree diagonal, so looking up can be a pain. But they are great for doing terrestrial surveillance, which is where a 80x200mm zoom lens excels.
I have found that I can see as deep (in terms of magnitude) with my lowly 70mm Pronto/PVS-7 combo as I can with my 10 dob and no night vision. A great general purpose combo is PVS-7 with a short tube refractor having an objective in the 80 to 120mm range.
If you need or want to use filters, especially narrow band filters, such as a 12nm Ha, aperture and fast focal ratio are king. Here I find my 10in dob with a .63 focal reducer works best. And bigger would be even better. It is big enough to give bright views, yet has a wide enough field of view to observe many nebula. One problem, of course, is portability. The views through a bigger dob must be fabulous, but if over 10 or 12 inches, portability can become a limitation. The second problem is that the field of view gets smaller as the telescope gets bigger (due to increasing focal length). For example, I was trying to observe the North America nebula one night in the 10" dob. I had a very hard time finding it. And when I did find it, all I could view was a portion at a time. Even though the NA nebula stands out when viewed with a smaller scope, it looks like any one of a million others when you can only see part of it. But hey, the view was bright.
NV with SCTs (8 and 10inch in my case) is great for looking at globulars and galaxies. M15 is spectacular. The problem that I have with SCTs is that I enjoy NV most for scanning, and the limited FOV of an SCT makes scanning frustrating. A .63 FR helps, but not enough IMO. But, now that I have looked through an SCT with NV, I cant bear to look through it with a glass eyepiece. Using a glass eyepiece in an SCT is like going blind (unless you are looking at bright objects like the moon and planets of course. There glass is the only way to go.).
So this brings me to what I think is probably the best compromise, a 6 or 8in reflector: The jack of all trades and master of almost none. It is small enough to be portable and can be easily mounted or even hand held. In my case, this is a AT6IN. I adapted it to a homemade dob mount so that I could use it off a table. Using a 12nm ha filter and a .63 focal reducer, it has a wide enough field of view to observe even the largest nebula, while having enough light grasp to give reasonably bright views. Without the FR and ha filter, it has enough focal length to recognize that distant galaxies are galaxies, but not much more. Basically, it will leave you wanting for other more specialized scopes, but it is an excellent place to start, and is the one I use the most.
Edited by Rickster, 25 March 2017 - 01:30 PM.