Thanks so much One Day for explaining this! So, for a low magnification straight tube as used for DG, a 30mm tube would be best. But for my .375, I could use a 2.5-10 x 44 (or 50) as I have been using for years in a 1” tube on my .338 and there would be no handicap as far as low light shooting goes compared with a 30mm tube? I generally hunt elk in/next to heavy timber and have never had an issue with not being able to see an animal through the scope in low light conditions AND without a lighted reticle! Maybe the heavy timber in Africa is more dense?
2.5-10 x 44, 1" = 2.5-10 x 44, 30 mm? Theoretically: yes. Practically: not always...
From a light transmission perspective, and without getting too deep in laboratory-level technical discussions, a 2.5-10 x 44 (or 50) 1" tube scope will provide the same optical services as a 2.5-10 x 44 (or 50) 30 mm tube scope, ALL OTHER CHARACTERISTICS BEING THE SAME.
Now, truth be told, as I discussed on other threads, and as pointed out by
@Bert the Turtle, this is not always true because all other characteristics are in fact not the same, and even though most all reputable manufacturers now use Schott glass, coatings make a huge difference in light transmission/diffraction/refraction/reflection and all Schott glass does not result in the same coated lenses...
There is no escaping the fact that German/Austrian-made top level Leica, Swarovski, Schmidt & Bender, Zeiss are better than anything else, including Hungary made Schmidt & Bender, US made Swarovski, Japan made Zeiss, US made Leupold, Vortex, etc. because the leading edge coating techniques, compounds and vapor deposition processes are so proprietary that they are not shared with even subsidiaries outside of Germany/Austria... (Note: the same applies to photography where Leica lenses remains unsurpassed by Canon, Nikon, etc. and scientific optical instrumentation where Zeiss reign).
So, theoretically, a 2.5-10 x 44 (or 50) 1" tube scope = a 2.5-10 x 44 (or 50) 30 mm tube scope in term of 7 mm light beam transmission, but top level 30 mm scopes are still better than most 1" scopes because they benefit from the latest coating technologies.
Is the difference worth YOUR additional $2,000? Some will say yes, some will say no.... What I can say is that there IS a visible difference at dawn and dusk. High noon is different and does not count: even mildly polished Coke bottle bottoms work. To see the difference, buy in winter and test on the parking lot in the first and last 15 minutes of the light. Chances are you will go OMG
2.5-10 x 44 on .375 H&H. It depends, but mostly yes...
My own .375 H&H wears a Leica ER i 2.5-10 x 42, so I would be hard pressed to say no, right?
But observe that I do my Buffalo hunting with an open sighted double .470 NE, that I will use on Elephant too in 2022, and I will use my .416 Rigby with Leica Visus 1-4x24 i LW on Lion in 2021. What I mean to say is that I do not expect to use my .375 H&H as an up-close charge stopper (which the caliber was never designed to be to begin with).
Therefore, a 2.5x magnification at the low end is fine on my .375 H&H.
If my .375 H&H was my only DG rifle, and if I wanted to be able to use it as an up-close charge stopper, I would want a lower magnification of 1x (hence a straight tube scope) so I could shoot with both eyes open.
Notice that I say "if I
wanted to be able to use it as an up close charge stopper," because whether I would ever "
need" to use it as such is an entirely different discussion
In summary...
I believe that any reputable 2.5-10 x 44 scope in the up to $1,500 range: Leica, Swarovski (Austria or US made), Schmidt & Bender (Germany or Hungary made), Zeiss (Germany, US or Japan made), Meopta, Leupold, Night Force, Vortex (well, maybe not the China made low end...) will work well on a .375 H&H, whether with 1" or 30 mm tube. The real ideal would in my mind be the classic 1.5-6 x 42 but I could not do it on mine because its true magnum length action is too long and I had to go with the slightly longer 2.5-10 x 42.
For a .375 H&H, I personally believe that in the up to $1,500 range, including some amazing deals for new old inventory, most
clients are better served with the light gathering ability of the 42 / 44 mm objective of a scope going down to 2.5x, rather than the low variable 1x of a straight tube scope, because
most clients will benefit more from the ability to see than they will need the ability to stop.
A PH choice is likely different...
In the end, I often reflect that even a Japanese 2020 Zeiss or Hungarian 2020 Schmidt & Bender is light years (pun fully intended) ahead of my 1980's Zeiss and S&B's; and that my same era Swarovski's do not even compare to a 2020 Chinese Vortex (early Swaro glass was really lesser than Zeiss or S&B), so I fully agree and concur that one does not need to spend the upmost $3,500 on glass.
I totally discourage spending $500 on glass, but in reality there are tremendously useful scopes in the up to $1,500 range and, in truth, they are plenty good for the job.
Sure, it is breathtaking to use my new Leica 10x42 Geovid HD-B 3000 binoculars, but my 1978 Zeiss 10x40 BGA binoculars worked absolutely perfectly for my three 2018 and 2019 safaris, and would have worked just as well until I die. The same goes for my 1980's Zeiss and S&B 1.5-6 x42, and my new Leica 2.5-10 x 42 and 1-4 x 24. The new Leica's were a treat, not a need...
PS:
of course, if money is no consideration, and you have a loose $3,500 burning a hole in your pocket, my recommendation would be Leica Magnus 1.5-10x42 i; Zeiss Victory V8 1.8-14 x 50; Swarovski Z8i 1.7-13.3 x 42 (even though I can't see for the life of me why anyone would want more than 10x on any big game hunting rifle) but make darn sure that their tube is long enough to fit onto your action if you use a true magnum length action...