I have seen the HorseHead from home ay SQM 18.8 with NV and a UHC-S filter (dual 50 nm band) with a 10" dobsonian. I cannot see it without NV even if I use a 24" dobsonian.
The horse head is visible in the 24" under SQM 21.5 with a H-beta filter and is comparable.
However however...however.... All objects are better (definitely better) in the 24" with NV than in in the 10" with NV. The difference is large and I cannot find any way in which a superb NV with the 10" can outperform a good NV with 24" (whichever location and target).
For example, the ink spot (H-alpha is not the only thing), i.e., NGC 6520 and Barnard 86 show a lot more details in the 24". You get the same level of clarity, but in one case at 42X and in the other at 115x (so one see three times finer structures).
There obviously is a sweet spot between high NV specs and greater diameter. One can spend 10k in NV and 2k in the telescope, or 4k in NV and 8k in the telescope or some other combination. The two extremes are not going to be the best.
Djorgovski 2 and NGC 6520 (ink spot).
Sumerian 10".
- With the intensifier in afocal, with the Paragon 30 mm (42x), the globular is glimpsed in the center of a quadrilateral of stars. The ink spot (NGC 6520/CB 107) is seen with a fairly well-defined outline. Switching to Delos 17.3 (72x), the globular cluster is seen a little better, but the ink spot is a little worse.
- Without the intensifier, with the Delos 17.3, the ink spot can be seen but more blurred. The globular cluster, on the other hand, is at the limits of perception. With the Ethos 13 (96x), the cluster is seen slightly better but still at the limits of perception. The ink spot is large but still not well-defined in shape and edges.
Zen 24".
- Without the intensifier, the ink spot can be seen very well with the 60 cm aperture, and the globular is seen well with some background glow, better than with the intensifier in the 10".
- With the intensifier at prime focus (115x) one can see the ink spot very well and with sharp edges—the globular resolves into stars.