The light transmission storry...
This bears repeating:
... You’ve lost the ability to judge horns with your binoculars long before you lose the ability to shoot accurately...
This is why when optics were still designed based on technical data, as opposed to marketing hype, the ideal combo in the 1970's for stalking in Europe was Zeiss* 7x42 binoculars (6 mm light beam at the ocular) and Zeiss* 1.5-6x42 scope (7 mm light beam at the ocular at full magnification), so that you could see just a little better when transitioning from judging with the binocs to shooting with the scope.
Folks who sat in "hochsitz" (high seat tree stands) or "miradors" (elevated hunting blinds) would generally use Zeiss* 8x56 binocs (a lot bigger and heavier) to have a 7 mm light beam at their ocular.
With these, you could see and shoot by half-moon light in the open, or by full-moon light in the forests, which was legal in Germany, France and many places in Europe in the 1970's. Full-moon light in the snow was just magical, you could actually see colors through Zeiss* optics.
*
in those days, Swarovski produced only the Habicht line, and their yellowish coatings were significantly inferior to Zeiss'; Lecia were not producing sport optics; and S&B were not very well distributed outside of Germany. So Zeiss was it, if you wanted quality.
This mattered, because it was possible to hunt at night, and this is why light transmission was so CRITICAL, and how the imperative for light transmission was created, and passed on.
When I moved to the U.S. on the East Coast, in the 1980's, I hunted for about 10 years with friends in Lycoming County, Pennsylvania, in the hills of Cogan House above Williamsport. I remember my friends bewilderment looking through my Zeiss binocs and scope. Their Leupold / Bushnell / Bausch & Lomb / etc. typically became about useless around end of legal shooting time at dusk, while mine would still allow judging a deer and taking aim (but not shooting because it would have been illegal) at deer in the open fields through most of the night when we had at least half moon.
Those were rubber armored B/GA T* 1980's generation Zeiss optics, transmitting typically 80%+ of the light through best-at-the-time coatings.
So.......... is today's 90%+ best-in-class light transmission necessary?
Not really, if you cannot hunt before 30 minutes prior to dawn and past 30 minutes after dusk, i.e. legal hours in most definitions.
And while best-of-best vapor deposition coating technologies and chemical formulae are more jealously guarded by Zeiss, Leica, Swarovski, Schmidt & Bender than nuclear secrets (they do not even share them with their partners/subsidiaries: Zeiss China, Swarovski USA, Schmidt & Bender Klassic [Hungaria], Meopta, Steiner, etc.), technology as a whole has progressed by leaps and bounds over the last 40 years, and today's even cheap China-made optics use Schott BaK glass, and are CNC polished and multicoated. So, 2020's cheap optics are as clear and transmit as much light as 1980's top-tier optics, typically in the 80%+ range.
This essentially means that from a glass perspective, today's Leupold, Night Force, Vortex, etc. provide all the light transmission necessary to hunt during most jurisdictions', and especially the U.S.', legal hours.
There is no doubt that only lab instruments can differentiate between 90% and 93% light transmission, so you may reach the end of return on light-transmission investment between Zeiss V6 and V8, or Swarovski Z5 and Z8, notwithstanding greater zoom range, which may or may not be meaningful (do you really need 8x on a DG scope?), but there is no doubt either than you will see a difference between 80%+ and 90%+ light transmission at dawn and dusk. Lord knows I love my old 1980's Zeiss 10x40 B/GA T* and they still reside in my truck, but there is "no comparison" with my 2020's Leica Geovid 10x42. And that is a fact.
Can I still hunt anything, anywhere, at any legal hour with my 80%+ light transmission Zeiss 10x40 B/GA T*? Heck yes! Can I see better with my 90%+ light transmission 2020's Leica Geovid 10x42? Heck yes! Is 90%+ worth paying 2 or 3 times more than 80%+? Sure, if you can afford it and you perceive the value, but not really from a pure light transmission perspective if you are limited to legal hours.
So why should you pay 2 or 3 times more for Zeiss, Leica, Swarovski, Schmidt & Bender?
There is an answer to that: light transmission is not the only thing!
Long ago, before I decided to stop wasting money on buying three times and replacing twice, I had a top end Bushnell scope. It fogged. I hunted with a friend who had a Leupold, I had to loan him my rifle to take the second shot after one of his two cross-hairs broke. I tried to help a friend sight his Burris I think it was, no two clicks had the same value, etc.
I bought a pair of Vortex Kaibab 18x56 binocs. That was before the Razor existed. Great light transmission. No complaint on this front. But the diopter adjustment changed ever so slightly when the binocular focus was adjusted. Annoying as heck for my 60+ years old eyes when scanning a terrain compartment. I checked two other pairs, same problem. After a couple of Arizona hunts my son was all too happy to get them and I bought a pair of Swarovski 15x56 SLC...
I bought a Vortex Razor 20-60x85 spotting scope. Great light transmission. But the image is soft. It is great at the shooting range to spot steel plate shots at 1,000 yards, but my Zeiss Dialyt 18-45x65 is much sharper and a lot more reliable to judge trophies at a distance. I take the Zeiss when I hunt...
Leupold sure know how to make scopes (even though, objectively, their coatings hence light transmission is noticeably below Zeiss, Leica, Swarovski, Schmidt & Bender), but I have no idea where the myth about Leupold being more reliable than Swarovski comes from. I understand that opinions are powerful, but where is the data?
From personal experience, what I can tell you is that the Zeiss/Hensoldt on top of the German army G3 were bullet-proof; that the Swarovski/Kahles on top of my SSG69 has been indestructible; and that the Schmidt & Bender on top of French, and most throughout the world, special forces' rifles were/are stronger than the rifles they are mounted on.
Sure, anything can break, but I am not aware of FACTS when it comes to Swarovski being supposedly less rugged than Leupold, or NightForce, or etc. As to internet lore..................................
So, glass polishing, precision of assembly, internal components materials (metals vs. plastics), internal adjustments, quality control, workforce experience, etc. all play a part, and this is where you get your money's worth, in addition to light transmission.
In summary, what do you get when upgrading to Zeiss, Leica, Swarovski, Schmidt & Bender? Better light transmission (better coatings) and sharper image (better polishing & precision assembly) for sure; in most cases magnesium internal components (although I will agree that modern polymers are light-years ahead of cheap plastics, and will do too); and higher quality control, although I agree that Leupold is probably on par as regards mechanical characteristics.
So, is it worth upgrading to Zeiss, Leica, Swarovski, Schmidt & Bender? Yes, if you can afford it. Few things in my mind justify borrowing, but I will argue that quality optics that will last you a lifetime are worth the interest rate, just as much as a truck or a house.
Should you stop hunting if you cannot afford Zeiss, Leica, Swarovski, Schmidt & Bender? Heck no! It is a very, very, very rare case, when you could not bag your trophy due to your optics not being the absolute very best tier.
This of course does not mean that you can go cheap, as some optics out there barely meet "Coke bottle bottom" quality and many endure catastrophic field failure, which are the reason why unconditional lifetime replacement warranty policies leave me cold, because my own goal is to purchase equipment that will not fail, as opposed to equipment they will be replaced after it failed...
