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Optics 101 On a basic level, all riflescopes work the same. Light rays enter the objective lens, which magnifies them. This upside-down image travels to the erector lens system, which flips the image right-side up and further magnifies it. The ocular lens magnifies the image a final time, then projects it to your eye. However, all scopes certainly don’t perform the same, optically or mechanically.
FRONT FOCAL REAR FOCAL WHATS THE DIFFERENCE?
For a Balanced Understanding of ScopeDesign, Consider the Optical Triangle The three elements of the Optical Triangle: 1.Magnification 2.Field of View 3.Eye Relief
Critical Optical Properties In a riflescope, getting the maximum amount of pure light to your eye is critical. At Leupold, we call this light management. The following are critical optical properties to look for in a riflescope, to determine how well it manages light.
Contrastis the best indicator of proper light management. Resolution and light transmission (often mistakenly called light gathering) enhance contrast while glare degrades it. Ex. black & white target together will show both colors distinctly versus gray.
Resolutionmeans a crisp, finely detailed image. Without good resolution the remaining optical elements are useless. Ex. Ability to see fine print on targets down range.
Glareis stray light reflecting off internal parts of a scope that enters the light path. Excessive glare diminishes all other optical properties.
C O N T R O L L I N G G L A R E Glare disturbs the focused light beam passing through the scope from the image to the eye.
C O N T R O L L I N G G L A R E • Glare can be reduced in a scope by: • Eliminating all reflective surfaces inside the scope • Using light baffles within the scope • Applying anti-reflective coatings to the lenses of the scope
Light Transmission is the measure of how much pure light makes it through the lenses before reaching your eye. It’s affected by the efficiency of the glass, the quality of anti-reflective coatings, and the control of glare.
L I G H T T R A N S M I S S I O N Three things determine light transmission: • The glass used in the lenses • The use of an anti-reflective lens coating • Effective use of the lenses in the scope
Anti-Reflective Lens Coatings Improve Light Transmission Index Matched Lens Coatings. That's Leupold's New special lens coating that reduces the reflection of light off the front objective lens of the scope. Each lens coating is matched to each lens composition. Some scopes have as many as 7 different glass types. The net effect is to increase your low light visibility by about 10%, when compared to a single or multi coated scope. Index Matched is available on selected Leupold models.
U N D E R S T A N D I N G P A R A L L A X • Parallax occurs in a scope when the reticle and the image are not focused on the same point. • Parallax causes the image to be unclear or to move in relation to the reticle. • A scope with parallax can produce inconsistent points of impact.
IN FOCUS(No Parallax) Object image falls precisely on reticle (focal) plane
OUT OF FOCUS(Parallax) Object image not on reticle (focal) plane
Exit Pupil The exit pupil is the diameter of light transmitted to your eye. You can see the exit pupil by holding up the scope at arm's length. It's the circle of light you see in the ocular lens. If you don't understand how it affects low light visibility, you can't make an informed purchase.
Exit Pupil First, the mathematics: Figure a scope's exit pupil by dividing the objective lens diameter by the magnification. For example, 50mm divided by 10x equals a 5mm exit pupil. In typical low light situations, the human eye can only handle about 5mm of light. So Leupold engineered the Large Objective scopes to deliver an exit pupil of no less than 5mm at the highest magnification. (Remember, Leupold uses the entire objective lens.) This means you get the maximum amount of available light for tough, low light shots.
U N D E R S T A N D I N G M I N U T E OF A N G L E • Important terms to know: • Angular Measurement – how to measure an angle. • Degree – the largest unit of angular measurement. There are 360 degrees in a circle. • Minute (of Angle) – a smaller unit of angular measurement. There are 60 minutes in a degree.
Lenses Leupold scope lenses are coated to reduce light reflection and light absorption. They should be cleaned as carefully as you would clean a camera lens. Use a lens brush to remove dust. If the lens is dirty, clean with pure alcohol, Windex, high-grade pharmaceutical acetone (keep it off of wood stocks), or pure water on a cotton swab.
Windage & ElevationAdjustments These adjustments are permanently lubricated. Keep turret caps on when not adjusting to keep out dust and dirt. However, Leupold scopes are permanently sealed even when the caps are off.
Eyepiece Adjustments This adjustment is permanently lubricated. It can be rotated as far as it will go in either direction and will not unscrew due to an internal Anti-back off ring.
Seals All seals are permanent and require no maintenance.
Scope Exterior Leupold scopes are made of a tough, aircraft-type aluminum, anodized for a smooth, glossy black, matte black, or silver finish. No maintenance of any kind is required, except to wipe off dirt and fingerprints.
Power Selector Ring No lubrication is required. Do not attempt to loosen or remove the hex head screw in the power selector ring.
FIXED Less of a chance for ranging error when using Mil Dots (Front focal variable) Most military snipers use a fixed. ( Standardization and they train for the long shot) They operate in a non permissive environment. The longer the shot the safer they stay. Military sniper gathers intelligence as well, but is usually with his spotter. Very rugged, less moving parts. (Military mission profile is brutal ). VARIABLE LE snipers are sometimes the only source of intelligence for the entry team, and need the ability to see at different powers. Does not become a factor for error if not using Mil Dots.( Again, front focal eliminates error all together.) More versatile(Rural to City). This is why the military employs variables for urban warfare. Variable vs. Fixed Military vs. Law Enforcement
Accuracy in Variable Scopes With Leupold variables, there is virtually no movement of the point-of-impact. Such accuracy is possible because of our extremely close machining tolerances, which can be as small as 5/10,000ths of an inch (.0005"). That’s five times thinner than an average human hair. Another important factor is the computer-aided design of optical and mechanical systems inside our variables, which results in unparalleled performance.
“Track-Out” To prove repeatable accuracy, you must be able to shoot a tight group at each power setting...ideally with a single point-of-impact. If you can’t achieve this with your variable, you have a “track-out” problem. (Your point-of-impact varies from power setting to power setting.)
Myth vs. Reality • Larger Objective Lenses guarantee better light transmission. • The most expensive scope is the best. • Rings and Bases are all the same. • The better the scope, the less I have to train. • Track-Out problems have nothing to do with poor shooting habits.
Myth vs. Reality • Keeping an accurate Data log is the snipers best tool for tracking both rifle and scope performance/ problems (courts will request data books should you one day make the shot) • Reducing a head target on the Xerox machine by half is not the same as shooting double the distance. (I have actually seen this done in some sniper programs)
Myth vs. Reality • The more magnification, the more accurate. • 30mm tube allows more light transmission than a 1” tube.
Mounting a Scope Mounting the scope isn’t all that tricky. But it is exceedingly important that you do it right. Here are some easy tips to follow. Select quality mounts. Install according to instructions. Do not use scope as a lever when installing rings use a wooden dowel or Leupold ring wrench. Ensure proper ring alignment. Always use the right length screws when mounting the base to the rifle.
Mounting a Scope Where cross-slotted screws are involved, at least half the scopes mounted at home are installed incorrectly simply because household screwdrivers don’t fit the scope-mount screw slots. Use a high quality screw-driver of exactly the right width and blade thickness. Of course, this problem is eliminated whenTorx screws and wrenches are used, as is the case with Leupold rings and bases.
Common Problems Problem: Scope's adjustment will not travel in a straight line. Caused by: Too much Windage and elevation dialed into scope causing erector system to contact the inside of the maintube. Solution: Use windage adjustable base and/or shims.
Common Problems Problem: Not enough elevation adjustment after zeroing the rifle. Caused by: Rifle's receiver is not in proper alignment with the barrel. Solutions: Use tapered mount base (Leupold Long Range STD). Use a shim beneath the rear base.
Common Problems Problem: Scope is mounted too far forward. Shooter cannot get proper eye relief. Caused by: Scope cannot be moved rearward because the objective bell contacts the forward ring. Solution: Use a reverse front mount base or an extension ring. (available in STD and Dual Dovetail systems). Make certain the length of pull on the rifle is correct for the shooter. Shorten stock if necessary
