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Six-Point Bull Session

3/8/2010

RENO, Nev. — Dr. Wayne van Zwoll is one of America's most respected gun writers and his column "Rifles and Cartridges" has been a popular feature in RMEF's member magazine, Bugle, for 21 years. Few of his fans realize that van Zwoll also was one of RMEF's first field directors during the organization's infancy.

Now a full-time journalist, van Zwoll has published more than 2,000 articles and twice that many photos for more than two dozen magazine titles, including Sports Afield, Outdoor Life and Field & Stream. He also has authored 13 books on hunting, shooting and history. He has guided big game hunters in Utah and Wyoming, hunted on five continents and shot competitively for much of his life, winning two state prone titles and qualifying for the final Olympic smallbore tryouts in 1972.

For today's Six-Point Bull Session, he puts all that experience to work providing insights to optics for elk hunting.

Enjoy!

Point 1: Why is the 3-9x40 scope still popular?

van Zwoll: Half a century ago, more 3-9x scopes were sold than any other. While magnification is creeping up, almost every scope-maker still offers a 3-9x. No wonder! It's still arguably the best magnification range for big game hunting! At 3x you get a big field of view for quick aim, and such a big exit pupil that your eye can't use all the light. At 9x, you get more magnification than you'll need for most shots. You're smart to carry any variable near the low end of its range. An elk you surprise up close won't tarry to let you crank the power down. But there's usually plenty of time to dial up magnification for a long poke — if you must. For most elk hunting, you won't need more than 4x. I recall killing an elk at around 300 yards. I had lots of time to add magnification but left my 3-9x at 3 power, because there was no need for more. The 40mm objective in traditional 3-9x scopes is my choice because it allows for lower scope mounting than do the bulkier (and heavier) 50mm front ends. The 50 has no more field, and brightness improves only at high magnification in dim light.

Point 2: What makes a scope bright?

van Zwoll: Three things contribute to brightness in a scope: glass quality, lens grinding and polishing, and anti-reflective, anti-refractive coatings. Glass quality has improved over the 400 years since Galileo first gazed at stars through glass. Schott glass, made in Austria beginning in 1884, set the standard for lenses in early rifle-scopes. Now top-quality glass comes from other sources, too. Specific types of glass are used in lens systems to bring the brightest image to your eye. Grinding and polishing to close tolerances matter as much as glass type and quality. So do coatings. An uncoated lens loses up to 4 percent of incident light at each air-to-glass surface. Seventy years ago a Zeiss engineer found that magnesium fluoride coating reduced light loss. Now lenses wear many color-specific coatings. A fourth factor also affects brightness: Exit pupil is the diameter of the pencil of light you see when you hold a scope at arm's length. Determine its diameter by dividing magnification into front lens diameter. The bigger the exit pupil, the brighter the scope — up to the diameter of your eye's pupil (7mm maximum, in the dark). In a variable scope, as you dial up power, you reduce exit pupil size, and there's less light reaching your eye.

Point 3: What is a fully-multi-coated scope?

van Zwoll: When light passes into and out of a lens, it is reflected and refracted. Series of uncoated lenses, such as in a rifle-scope, can lose a huge amount of light, making the image dark and ill-defined. To boost light transmission, German optical engineer A. Smakula started coating lenses with magnesium fluoride in the 1930s. The Nazis seized his work; but after the war, coated lenses were widely adopted. More sophisticated coatings followed, specific to light of different wave-lengths. Manufacturers added them as microscopically thin layers to further trim light loss. A scope with coating on every lens (not just on the visible front and rear lenses) is said to be fully coated. A scope with several coatings on each lens is fully multi-coated. Coatings are not tints (which rob light!); but they do impart color to the glass — typically purple, blue, green, rose or straw, sometimes in combination. When you buy a scope, make sure it is fully multi-coated! If it is not, you're not getting the brightest image possible from your investment.

Point 4: What do the numbers mean?

van Zwoll: You've seen 4x as a scope designation. Intuitively, you figure that means the lenses magnify your target to four times its real size. You're right. A 4-12x variable scope gives you a choice of magnification, from 4 to 12. A number after the "x" is objective lens diameter, in millimeters. A 4-12x40 has the same magnification as a 4-12x50 of the same design, but a smaller front end. Field of view, which depends on power, is the same at any setting for these two scopes. Objective diameter does affect exit pupil size, however. Big objective glass yields a big exit pupil, which can deliver a brighter image when your eye is fully dilated. At modest magnification in good light, big front glass can't boost brightness. Its only advantage then: a generous "eye box" — that place behind the scope where your eye finds a full field of view. Power range imposes another number. After decades of "three-times" magnification, we now have four-, five-, even six-times. So instead of the top power being three times the bottom, as in a 4-12x, the range is broader. A "four-times" scope could be a 4-16x or a 5-20x. A "six-times" scope might give you a range of 2-12x or 4-24x.

Point 5: See-through mounts: salvation or scam?

van Zwoll: When rifle scopes were new, and hunters used to iron sights were learning to aim through glass, it seemed a good idea to retain access to irons. Swing-away and quick-detachable bases were engineered so if a scope failed or fogged (a real possibility, early on), you could get the scope out of the way quickly. See-through scope mounts were another option. The tunnel under the rings gave you instant view of notch and bead for quick shots, whether or not the scope had a problem. QD mounts survive, mainly on rifles for dangerous game, but pivoting mounts have faded. See-through rings should follow. First, scopes are more reliable now; I've not had a scope fail me in decades, and most new bolt rifles don't even wear iron sights. Secondly, see-through mounts put the scope high, forcing your cheek off the stock — a recipe for slow, inaccurate shooting. Lastly, modern 3x or 4x scopes, mounted low, are very fast. They're actually faster than iron sights, because the reticle is in the same apparent plane as the target. Set your scope up low and forward so you get a sight picture as soon as the butt touches your shoulder. Then practice!

Point 6: How do I get the most out of my scope?

van Zwoll: A modern rifle scope is a hardy instrument, but it does require some care and adjustment. First, keep fingers and gun chemicals off the glass! To clean lenses, wipe in soft circular strokes with lens tissue, moistened with lens fluid. When installing a scope, make sure rings are aligned perfectly before pressing the scope into them or cinching. Tighten ring screws alternately, as you would lug nuts on a wheel. Mount the scope well forward. On a hunt, you'll naturally lean into the rifle, especially in prone and sitting. Many hunters set scopes too far back for field positions, slowing their aim and occasionally banging their brow. Make sure that the reticle is "square." A tilted reticle can cause you to tip the rifle, impairing accuracy. Adjust the ocular lens or eyepiece by pointing the rifle at the northern sky, where your eye has nothing on which to focus. Close your eyes, then open them quickly and turn the eyepiece until the reticle becomes sharp. Check and refine. You shouldn't have to adjust focus of the reticle again. If your scope has an adjustable objective (front sleeve or turret dial), match its setting to the distance to sharpen target focus and eliminate parallax at that range.