Mauro was almost always going for a decent amount of magnification on a lot of targets; more than most of us tend to use with our NVDs.
For non-narrowband objects it makes a lot of sense. I never go under 2x less
magnification than I tend to use with glass. With glass I tend to use an 8mm Delos for galaxies, so on these I need a 16mm equivalent eyepiece. That's a TMB-barlowed OVNI-M. For larger galaxies overviews (for which 16-26mm eyepieces are used when using glass just to get enough field of view) I tend to use either the plain Paracorred OVNI-M or even swap the Paracorr for a Nexus reducer.
If you go well below that magnification then the fact you can see sharper with mesopic vision does not compensate the smaller image scale.
That's the beauty of scotopic vision: it's extremely fuzzy, but very, very, very sensitive, allowing you quite some image scale to compensate for its fuzzy nature, and for apparent surface brightnesses brighter than roughly 26 mag/arcsec² is fairly noise free (an NVD could only dream of the SNR).
Of course you do need to be perfectly dark adapted and need to hone your averted vision skills (and patience!)
An NVD in a dark sky is just another tool in the box (and needs another eye). Some things that are really hard with glass (like the really thin dust lane in NGC 7814) are easy-peasy in the NVD, most Arp features in Arp galaxies are also easier to pick out, some galaxies that are just blobs with glass turn into obvious spirals, and the cores of elliptical galaxies in rich galaxy clusters are just too many to count (seriously...you can start to barlow to get more magnification and some fuzzy stars at 'regular power' turn into galaxies, revealing that you were seeing too many to sketch or even count). And it's not always the bright stuff that's better with the NVD, I'd count the tighter but wider spiral arm of NGC7479 as faint but it was more apparent in the NVD and obviously split in two (with Astronomik L1 filter and OVNI-M in prime in a Paracorr).
But other things are easier with glass...we had stunning views of M33 this weekend where with glass you could see two
faint but wide arms under the bright arm going to NGC 604, and as a result it was impossible to fit M33 in the FOV of a 26T5 in a 400mm Dobson. The NVD was most useful to pick out HII regions and smaller star clusters, but some of the larger star clusters in M33 were also easier with glass. And do what you want, the faint tidal tails thrown out of both components of M51 were just harder to see with the NVD; I can echo Mauro's experiences with that and not even the Astronomik L1 managed to change that (although it narrowed down the difference).
perhaps NV can detect certain ones at a low magnification
It's true that you can e.g. filter more aggressively with an NVD to get more contrast and compensate by using less magnification with NVD, but glass usually wins hands down for really large but faint contrast features in a dark sky. You'd be hard pressed to see Barnard's Galaxy with an NVD, even though it sticks out like a sore thumb in a 20x80 in a dark sky; in the NVD it's undoubtedly there
at high gain but then it's buried in the noise, and if you reduce the gain it becomes too faint. On the other hand, use the NVD with some more image scale and the HII-regions in it are easy and even detailed
in a large scope (as is M33's NGC 604), although it's fairly eerie to see extragalactic HII-regions float in apparent nothingness...
The most bizarre experience remains NGC 5053. It's a lot harder with glass but there is a definite glow behind the stars that you eke out of the background. With the NVD it looks like an open cluster, with all the bright stars immediately apparent but seemingly nothing else beyond them except a really faint but small glow in the middle that's really hard to see through the noise.
Edited by sixela, 18 September 2023 - 04:34 PM.