Two Great Truths About Optics

I’ve written a lot of magazine articles about optics, and for several years I even wrote a continuing optics column. I don’t claim to be an expert, but I know a little bit about optics. At least, I thought I did. Just last week, at the annual Outdoor Sportsman Group “round table,” Zeiss’s Kyle Brown gave us an update on new products. He started with two very astute comments.

The first one I’ve said wrong so many times that I’m embarrassed: “Optics don’t gather light; they manage light.” The second is something that I have long believed, but Kyle said it better and simpler than I ever have: “Magnification is over-rated!”

Managing Light

The “Twilight Test” Belies the Quality of Your Optics

On the one hand, this is another way of saying the same thing, but light is what it is. Optics don’t create more light. However, in that critical half hour before sunrise, good optics do manage available light and enable you to see better than is possible with the naked eye. Note, please, the word “good.” The obvious test is to go outside at dusk or dawn, check the light with your eyes, and then look through a quality modern optic. The image through the glass will be brighter than that recorded by your eyes alone. This is done through quality of lenses and coatings.

Magnifying lenses aren’t new; the first telescope goes clear back to 1608. In 1668, Sir Isaac Newton added the first internal mirror to reflect light into the lenses. Binoculars and riflescopes go back to the 19^th Century.

Lens Coatings Led to Revolutionary Improvements

Lens coatings, however, are products of the 20^th Century, and this technology continues to evolve. If you chance across a genuine antique optic, do the same test I mentioned above. If the glass is good the image may be clear, but you will not see enhanced brightness. Lens coatings prevent available light from being reflected away and transmit it through the lenses, allowing the optic to “manage” that light.

Coatings vary; many are proprietary and expensive—one reason why great optics are costly. However, if glass and coatings are more or less equal, then larger objective lenses “manage” light better than smaller objective lenses. So, a 10×50 binocular will be “brighter” than a 10×42 binocular.

Tradeoffs: Better Light Management Can Add Weight and Bulk

Unlike magnification, I will not say that brightness is over-rated… a major reason for spending extra money for extra-good optics is to gain just a couple extra minutes of visibility at dawn and dusk. Good glass costs, so you’re probably going to pay more for optics with larger objective lenses, and you will be adding weight and bulk, so there are tradeoffs.

But here’s another factor. Purely as a matter of design physics, the “European standard” 30mm riflescope allows better light transmission than the smaller American standard one-inch (26mm) scope tube. So, again with quality more or less equal, you are gaining light transmission (“brightness”) just by going to the 30mm scope, but you’re also adding weight and bulk. More frequently we are seeing 34mm and even 36mm scope tubes. Again, more weight and bulk.

When Choosing a Scope, Consider Your Priorities

European hunters are big on large riflescopes, but keep in mind that in much of Europe “shooting hours” don’t exist. Typically, we worry about a half hour before sunrise and a half-hour after sunset. Depending on cloud cover and shadows, good optics manage dawn/dusk light levels pretty well. In Europe, it’s perfectly normal to sit on stand long after dark, waiting for moonrise. This, to them, is what a big 30mm scope with 56mm objective lens is all about.

Just remember, a one-inch scope tube cannot manage light as well as a 30mm tube, and there can be diminishing returns: A one-inch tube gains less benefit from a huge objective than a scope with a larger tube. Additionally, the small, handy straight-objective scope that we think of as a “dangerous game” scope—like a 1-4x32mm—can’t manage light as well as a slightly larger scope with a bigger objective, regardless of quality. These scopes are great for stalking buffalo; more magnification isn’t needed, and max brightness is rarely an issue. However, this is also the type of scope we often put on, say, a .375 that we might take into a leopard blind, or on a .45-70 that we might use for black bear over bait. In those scenarios, light management is critical. You don’t need a “big” scope for such purposes, but you might be better served by a scope with a traditional objective bell and larger objective lens that offers better light management.

Magnification is Overrated

Riflescopes are becoming more powerful, a trend sparked in part by the current interest in extreme-range shooting and enabled by technical advances that make five and six-times zoom practical. Upper magnification settings in the high teens and well beyond 20X have been around for decades, but now these “high-range” variables are increasingly common.

Obviously, there are specialized purposes for these high-powered optics. Varmint hunting for small rodents like prairie dogs requires magnification; so does extreme-range shooting, regardless of what you’re shooting at.

Larger Images Can Mean Diminishing Returns

A larger image allows you to see better and makes precise shot placement easier. I’m not going to step back into the 60s, when variable scopes weren’t quite perfected and, for good reason, were widely distrusted. Back then, our best gunwriters would pontificate that “a fixed 4X was all you really needed.” I like magnification, but there are diminishing returns.

Although a larger, magnified image is easier to see and hit, what matters most is clarity of image, which comes down to quality of optics. Also, there are two problems with extreme magnification. As an inherent engineering constraint, as you increase magnification on a variable-power optic the field of view shrinks, making it more difficult to acquire the target and stay with it. With a variable-power spotting scope of, say, 20-60X, do you try to find a buck on a distant hillside at 60X? Uh, no. You start at the bottom, find it, lock in on the tripod, and then zoom in.

The other problem with high magnification is it magnifies everything: Heat waves, mirage, any and all wobbles, even disturbance from your heartbeat. Again, a variable spotting scope is a great example. At extreme magnification, a light breeze causes too much disturbance to resolve small objects (like antler tines and bullet holes in targets); conditions must be near-ideal to effectively use magnification much above 30X. On a smaller scale, binoculars are similar: Most people can hold a 10X binocular steady enough. Few people can hand-hold a 15X binocular steady enough to get real utility, although big binoculars are awesome when tripod-mounted.

What’s Best For Hunting? It Depends

In riflescopes there are situations where high magnification is useful, but in big-game hunting there are good reasons why the 3-9X (or thereabouts) variable has been so popular for so long! 3X won’t get you in trouble at close range, and 9X magnification is plenty for almost any shot at any range. These days, I often put a 2-7X or even 3-9X on my .375s. I don’t need the power for buffalo, but the .375 is a versatile cartridge; on smaller African antelopes there are times when the extra magnification can be handy, and a 2-7×33 or 3-9×40 “manages” light a lot better than a 1-4×32.

On one hand, magnification isn’t always necessary. These days I often use non-magnifying red-dot sights like the Aimpoint. They are fast and bright; at closer ranges they quickly prove how over-rated magnification really is.

 On the other hand, for hunting in more open country I do use the higher-range variables: 2-12X, 4-16X, 3-18X. Having the larger image right there at my fingertips is handy, but, honestly, it’s uncommon for me to actually use maximum magnification. In tight cover I keep scopes like these turned almost all the way down; in open country I compromise and leave them at about 6X. I can always turn up the magnification for a longer shot, but with heat waves and mirage it isn’t uncommon to be unable to use more than perhaps 12X.

I admit that I’m spoiled by magnification. Last year I acquired a gorgeous .270 by retired custom maker Joe Balickie. He built it some 25 years ago, and it came with the original scope, a vintage Leupold 2-7X. I would normally put a larger scope on a flat-shooting rifle like a .270. However, this rifle shoots tight little groups just the way it is, so I decided I’d leave it “original.” I took it to Namibia in July ’18. There were no “long” shots, certainly not by today’s standards, but I took several animals between 300 and 400 yards. This was an old lesson that was good to re-learn: The 7X image was plenty big enough, and although I’ve only had this rifle a year, it hasn’t yet missed. I couldn’t do any better with twice as much magnification.

 

When choosing optics, your environment and your priorities will help you determine what’s best for you. Magnification can be overrated, but not always, and, depending on when you hunt, it might be worthwhile to invest in expensive glass that will manage light more effectively. Remember, hunting and shooting aren’t one-size-fits-all sports; find what you’re comfortable with, stick with it, and don’t let anyone else try to force their preferences on you.