Combat Arms 2869 Grove Way Castro Valley, California 94546-6709 Telephone (415) 538-6544 BBS Phone: (415) 537-1777 ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ» º º º Scopes for Dopes º º º ÈÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍͼ I have compiled and written the following to help the reader learn something about rifle and pistol scopes. Since rifle and pistol scopes are the same for our purposes (and since I do not sell 3 pistol scopes a year), this talk will remain limited to rifle scopes mounted on .223 and .308 weapons such as the Colt AR-15, HK-91, SSG and FN-LAR. The information is also valid if you mount the scope on your typical hunting gun but I do not sell that kind of weapon and know little about them. First of all, let's discuss FIXED POWER scopes. If your shooting conditions do not vary a great deal (meaning that you are generally shooting at the same distance most of the time), you should choose a scope with a fixed magnification. A high quality fixed power scope in 4 to 6 power will cover everything you need to do out to 500 yards without having to fiddle with things and readjust the power setting on a variable power scope. I recommend that you consider a 6 power scope with about a 42 millimeter objective and a 4 power scope with a 32mm objective. VARIABLE POWER scopes are useful at low power in order to provide you with a wide field of view for close distances or wooded areas. The higher magnifications are used for longer distances in open areas for greater detail. Variable power scopes range from a 1¬ to 4 power scope to 2« to 10 power scope. The problem with variable power scopes is with the user. If you constantly shoot using the high power setting there you are wrong to buy the more expensive variable power scope. If that's the case, a fixed power scope is less expensive and is the right tool for the job. Another consideration with variable power relates to the field of view. Field of view is the measurement of the diameter of the field of vision seen by the observer while looking through the optical device. This measurement is determined at different distances from the instrument, depending on whether the product is a riflescope, spotting scope or set of binoculars. As a general rule, the higher the magnification of a particular instrument and the smaller the diameter of the objective lens, the more restricted the field of view will be. If the power gets too great, the field of view will be too small. At higher powers, a slight movement of the instrument results in a radical change in the viewing area. The field of view may also be influenced by several practical, rather than optical, considerations. Any time the distance from the eyepiece to the eye (called "eye relief") is extended, there is a corresponding narrowing of the field of view. This may be necessary in products such as riflescopes in order to prevent the riflescope from contacting the eyebrow during the recoil of the gun. In pistol scopes or other extended eye relief applications, the field of view will be further reduced. Riflescope field of view is determined at 100 yards (or meters if a European scope), while both spotting scopes and binoculars have their fields of view measured at 1,000 yards (or meters). Why do some scopes cost so much more than others? The secret is in the optics. Higher quality scopes use the very best optical glass to make the lens. The best raw glass blanks are then polished by skilled craftsmen into lenses of very close tolerances. The very best glass lenses are made in Europe. The accuracy with which any optical instrument registers an image depends on the quality of lens grinding and polishing. The primary silica glass material must be free of all impurities and the lens surface finish and curvature must be absolutely precise. The ability of the instrument to distinguish fine detail will be in direct proportion to the care taken in lens manufacture. Since lens quality is something that cannot be properly judged by the human eye, one should not expect to purchase a quality optic at a bargain basement price. Simply put, the more a lens manufacturer must put into the production of its products, the greater must be the price. Because optical lenses are highly polished, it is a fact of optical science that approximately five percent of the light that enters or leaves that lens will be reflected back upon itself. Should a particular optical device contain 10 or 12 different lens elements (like a rifle scope), the total reflected light could conceivably be as much as 50-60 percent. To prevent this loss of image, lens manufacturers coat their lenses with a special anti-reflective coating especially formulated for maximum light transmission of over 90 percent. This coating is of a specific type and thickness. The process involves molecular bombardment of the coating material in a vacuum onto the lens surface. This coating greatly reduces internal reflection and increases image contrast, which enhances the detail that the eye can see. It is impossible for 100% of the light entering the front of the scope to reach your eye. A cheap scope will have a darker image than one with a great refractive coating job done to the lenses. Also, the better scopes will enable you to have a brighter image and to continue to see under poorer lighting conditions, such as at dawn and dusk. One trick to help you in shopping for a scope is to look at the objective (the front end of the scope that gathers the light). The poorer the coating put on the lenses, the more the lens will act as a mirror and reflect your image. The better manufacturers use a magnesium fluoride coating on the lenses. Good scopes have a poorer mirror image, thus transmitting more light and a sharper, brighter image of the target to your eye. This coating material is easily discerned by its color, which is often seen as purple, straw or a faint green. The most common type of coating is magnesium fluoride but more exotic multi-layer coatings provide enhanced image transmission. The time, cost and quality control involved in the coating process seriously affects the final price of the unit. Since it is impossible to determine the coating's thickness or the type of coating used without laboratory instruments, you must trust the manufacturer's reputation. Bear in mind, that below a certain retail price line, the quality of the lens grinding, polishing and coating are unknown quantities and are generally inferior. Color fidelity is important and is related to lens quality and coating preciseness. Looking through a cheap scope, the colors will not appear true. This is critical in a wooded or jungle environment which already has reduced light. You want a scope which will withstand the recoil of the weapon and has its reticles ("crosshairs") centered. The scope should be dust proof and moisture proof. There must be very precise click adjustments to the scope. It is best if the scope has ¬, 1/3, or « minute of arc adjustments per click. Thus, one click on a scope with ¬ minute of arc adjustment with change the point of impact ¬ inch at 100 meters (109.36 yards). This fine adjustment becomes important at longer distances. If your shooting regularly includes distances greater than 500 meters, choose a scope with ¬ minute of arc adjustments, unless the precision is unimportant. Beware of the overuse of the term "twilight factor" in a scope's description. It is arrived at by a simple formula which only takes magnification and objective lens diameter into account. This is misleading because it leaves out important information about the lens coating, the quality of the scope tube, and the quality of the blackness inside the tube. Optical data say nothing about the quality of the scope! Just as the caliber and magazine capacity of a weapon tell you nothing about the accuracy of the piece, optical data does not necessarily equate with quality. If a salesman starts pitching numbers at you regarding optical data, walk away in a hurry because he simply does not know what the hell he's talking about but has merely memorized some data to impress you. The way to correctly use the twilight factor is to understand that the pupil of the human eye during daylight conditions will be open to approximately 2 to 5 millimeters and will increase its opening to 7mm in dark conditions to allow more light to enter the eye. A rifle scope will "funnel" light into an exit area for the eye to view the target. This exit area, referred to as the "exit pupil" by optical engineers, should correspond to the pupil of the human eye in dark conditions. The exit pupil of the scope can best be understood by holding the scope about two feet away from your eye. The small disk of light that appears in the rear ocular lens (the engineering term for the eyepiece) is the actual area your eye looks into the scope, not the entire rear eyepiece - only that small pupil area of light. The pupil of the human eye and the exit pupil discussed above should correspond very closely. so that the full amount of light concentrated at the exit pupil of the scope will enter the eye of the shooter. For example, a 6x42 scope (6 power magnification with a 42mm objective) will "funnel" its 42mm of light gathered from its 42mm objective six times (the power of the scope). The resulting final image is then concentrated into the 7mm exit pupil. To find the size of the exit pupil image in millimeters, simply divide the size of the objective in millimeters by the power; in our example 42 ö 6 = 7. This 7mm exit pupil is equivalent to the maximum normal opening of the pupil of the human eye (forget about the pupil diameter caused by opiates!). A 8x56 scope will "funnel" more light because of its 56mm diameter and will therefore appear brighter then the 6x42 scope. Extending this theory to its illogical conclusion, a 10x70 scope would be even brighter still, but how the hell could you mount a scope with a 70mm objective? Thus we can see that a 8x56 scope or a variable power scope with a 56mm objective set at 8 power is about the brightest we can expect. Such a scope will enable you to see your target under rather unfavorable dark conditions. Now that you know all of that, we can define twilight factor as the square root of the product of the magnification and the objective in millimeters. For example, a fixed 6 power scope with a 42mm objective has a twilight factor of: _______ ___ û x 42 = û52 = 15.9 Zeiss says the twilight factor can give you some measurement of the visibility of details in twilight. The higher the twilight factor, the better the visibility in poor light, with all other conditions the same. But this says nothing about the quality of the glass, the lens coating, the tube strength, etc. So, the better manufacturers suggest that you do not rely on the twilight factor when comparing scopes, especially when comparing different brand names. Early optical instruments had bodies made of brass but this material proved too heavy and tarnished easily. Modern optical devices use bodies constructed of steel, aluminum or synthetics. Should the scope tube be aluminum or steel? Steel offers strength and resistance to thermal expansion but can rust and requires a higher level of maintenance unless it is specially coated. Steel weighs more but it is stronger. Many gunsmiths will tell you that there is no substitute for steel. Aluminum has widespread usage in the optics field because it is lightweight, rustproof and resistant to wear. Aluminum expands more than steel when heated. This must be compensated for by a more rigid mounting system for the lenses so they will not more when subjected to variations in temperature. Synthetic materials offer lower weight, lower maintenance, high damage resistance and total thermal stability. The use of synthetic is found more in binoculars and spotting scopes. Expect to see riflescope tubes made from graphite and other materials. The modern scope mount clamping assembly places a high demand on the stability of the sight. On the other hand, the better manufacturers have a line of aluminum tubes that can withstand the pressures put upon them by the clamps. There are various grades of steel and aluminum and the simple truth is that the cheaper scopes use cheaper materials. Choose steel if ruggedness, stability and absolute accuracy are the criteria. If weight is the consideration, choose the alloy tube. The tube should be finished with several layers of plating and a baked enamel outside finish. This protects your investment in the scope. You don't want a finish that will wear and expose bare metal to the air. Who makes the better scopes? The Rolls Royce of scopes is made by Carl Zeiss of West Germany. They are in first place. There is a tie for second place, in my opinion, held by Swarovski, Schmidt & Bender, Hensoldt, Kahles, Steiner, and Nikon. These are all European manufacturers. The tie for third place goes to Leupold, who makes all of their scopes in America, and to Nikon, who makes its scopes in Japan. The higher priced Leupold scopes edge them towards second place. There is no sense in wasting your time discussing the quality of Nikon except to say that they are new to the rifle scope business. The Nikon scopes I have sold have been good value for the money and are priced affordably. The Nikon 3-9X scope has a 40 mm objective, ¬ minute of arc adjustment for windage and elevation, weighs only 16.06 ounces (455 grams), is 12.32 inches in length and has a field of view of 11« to 34« feet at 100 yards (as a function of the power setting). These values for the Nikon are included because they are typical of those found in the better scopes. In my considered opinion, Redfield is in fourth place and Bushnell and Tasco are in fifth. Somewhere farther down the line is Simmons. If you are putting a scope on the AR-15, consider Tasco's armored scope. Believe it or not, it is perfect for the job and is one of Tasco's finest scopes. It is also Colt's choice for the Delta HBAR and retails for $129.95 plus the $59.95 mount, thus saving you considerable money. I am amazed at Tasco's quality in this one particular scope (called their World Class series). Too bad it does not extend across their entire line. My suggestions are to choose a fixed power, lower magnification scope for use in the brush. The maximum power scope you can really quickly shoot off hand is 6 power, so a 6x42 scope is an excellent choice. Some people feel that magnifications higher than six power simply magnify the shooter's errors and make the shooter reluctant to fire a quick shot without support. The 8x56 style fixed power scope really should be used with support. The variable power scope in the 3-9 power category generally has a 42mm objective and there are quality variable power scopes with 56mm objectives. The 3 to 9 power variable should be set to 6 power at dusk and during dark shooting conditions. Remember that 42mm ö 6 = 7mm and 7mm is the magic number for the maximum normal opening of the pupil of the human eye! Use the 8 power setting if your variable power scope goes up to 12 power. The lower power settings of the variable permit better offhand shots while the higher powers make target identification easier. Select a scope with a 56mm objective only if you intend to shoot under dusk or dim light conditions, such as in a wooded area or under a jungle canopy and need such light gathering capability. A note regarding Zeiss scopes. All Zeiss scopes have a 30 year warranty, multiple layer lens coatings. Diatal indicates a fixed power scope while Diavari means a variable power scope. The Zeiss scope will withstand 1,000 g's in recoil forces with very negligible change in the point of impact. The scopes all have ¬ minute of arc adjustment for windage and elevation. There is no change in the point of impact with changes in magnification on variable power Zeiss scopes. All are fog free and sealed for protection from weather. Scopes with a 1" tube have their calibration in ¬ inch at 100 yards. Their 26 and 30mm scopes are calibrated for 1 cm at 100 meters.The 1" tube scope are more compact than the metric scopes. It would hardly be fair to have explained all of this and say nothing about binoculars, so let's turn our attention to them for a moment. Binoculars are really two separate monoculars, hinged along a central axis, about which the separate monocular halves can rotate to accommodate the varying separation between individual eyes so that the binoculars will fit any person. Center focus binoculars feature a central focus knob that moves both halves of the binocular simultaneously to adjust the focus of the instrument. Usually, one eyepiece has an individual plus or minus adjustment to make up for the slight differences in eye focus. Individual focus knobs eliminate the central focus knob and each half of the binocular is focused separately. The major difference between binoculars is in their basic prism system design. Traditional binocular configuration is the offset "z" shape of the individual binocular halves. These are called "porro prism" designs. The porro prism method of making binoculars gives the manufacturer a rather wide tolerance in fabrication without sacrificing optical quality. This means theat porro prism style binoculars generally cost less. The drawback is that porro prism systems are heavier and physically bigger binoculars. Another design method is called the "roof prism" style of binocular construction. They eliminate much of the porro prism design's bulk. Because both lenses of a roof prism binocular are in a straight line, the usual "z" shapped binocular tube associated with the porro prism method is eliminated. This results in a sleeker, straighter tube. Very precise toleerances are necessary when building a roof prism instrument and this results in higher costs. A negative aspect of the roof prism design is that it results in an overall loss 10 to 12 percent of the light transmission due to the nature of the prism system used. For the vast majority of people, this loss is inconsequential and is more than compensated for by the reduced weight and bulk of the more compact roof prism design. Here are the prices of the Zeiss and Schmidt & Bender scopes. This will give you some feel for what a truly good scope costs. If quality is important to you then stick with one of the better European manufacturers. Quality costs money. If you think you can get high quality at a low price, your parents lied to you. It ain't possible! ZEISS RIFLE SCOPES Fixed power - 1" tube 5210909920 4 power with 32mm objective 600.00 5210919920 6 power with 32mm objective 650.00 5210929920 10 power with 36mm objective 770.00 Fixed power - 26mm or 30mm tube 5210819908 4 power with 32mm objective 600.00 5210839908 6 power with 42mm objective 700.00 5210859908 8 power with 56mm objective 900.00 Variable power - 1" tube 5210979920 3 to 9 power with 36mm objective 1050.00 5210069920 1.5 to 4 power with 18mm objective 900.00 Variable power - 26mm or 30mm tube 5210979920 1.5 to 6 power with 42mm objective 1000.00 5210069920 2.5 to 10 power with 52mm objective 1160.00 SCHMIDT & BENDER RIFLE SCOPES Fixed power steel scopes: 001515 1« power with 15mm objective 690.00 043600 4 power with 36mm objective 730.00 064200 6 power with 42mm objective 770.00 085600 8 power with 56mm objective 870.00 124200 12 power with 42mm objective 890.00 Variable power alloy scopes: 014200 1¬ to 4 power with 20mm objective 930.00 016420 1« to 6 power with 42mm objective 1020.00 021056 2« to 10 power with 56mm objective 1230.00 01642S 1« to 6 power with 42mm objective - Sniper grade 1680.00 04025S 4 power Sniper with 25mm objective 1360.00 *** *** *** *** *** *** *** SPECIAL OFFERING *** *** *** *** *** *** *** ** Because the better line of scopes described above are really new to the San Francisco Bay area, Combat Arms is offering a special 20% discount to any BBS customer on any Zeiss or Schmidt & Bender scope if paid in advance in cash. A discount of 15% applies if paid by credit card. This offers expires December 31, 1989. ACKNOWLEDGEMENTS I am grateful to Zeiss and Schmidt & Bender for the material they provided. Also thanks go to Durwood Hollis for his article called "The Clear Picture on Optics" in the September/October, 1988 issue of Shooting Sports Retailer magazine. Richard M. Bash - Owner Combat Arms Castro Valley, California January 14, 1989