AR15 Scope Store - Scope term glossary

Glossary of Scope and Optic Terms

Adjustable Objective	The adjustable Objective allows operator to focus at distances over 100 yards and adjust for a condition called Parallax. Parallax occurs when viewing distant targets, and the reticle appears to shift or move. Scopes with adjustable objective lenses have markings that allow you to adjust the focus for specific ranges. This occurs when the image in the scope is in one focal plane, and the reticle is in another. Most scopes without adjustable objectives are factory set to compensate for parallax and focus at an optimum distance of 100 or 150 yards. Parallax is usually only an issue at magnification over 10 power.

Angle of View	The Angle of View is the angle between the left and right edges of the field of view at 1000 yards from the Binoculars' point of view.

Apparent Angle of View	The Apparent Angle of View is this same angle with the binoculars' magnification figured in, the Apparent is simply the (magnification x Angle of View).

Aperture	The size of the binoculars' objective lenses. The second number represented in the numbers describing a set of binoculars, measured in millimeters.

Binoculars	An optical device, such as a pair of field glasses or opera glasses, designed for simultaneous use by both eyes and consisting of two small telescopes joined with a single focusing device. Binoculars are available with fixed or variable magnifications.

Center Focus	A mechanism in Binoculars that allows both eyepieces to be adjusted at the same time, useful for rapid focus.

Close Quarter Combat	Close Quarters Battle (CQB) or close quarters combat (CQC) is a type of fighting in which small units engage the enemy with personal weapons at very short range, potentially to the point of hand-to-hand combat. In the typical CQB scenario, the attackers try a very fast, violent takeover of a vehicle or structure controlled by the defenders, who usually have no easy way to withdraw. Because enemies, hostages/civilians, and fellow operators can be closely intermingled, CQB demands a rapid assault and a precise application of lethal force. The operators need great proficiency with their weapons, but also the ability to make split-second decisions in order to avoid or limit friendly casualties. CQB is defined as a short-duration, high-intensity conflict, characterized by sudden violence at close range. (Wikipedia Excerpt)

Depth of Field	The portion of an image, between the foreground and background of the viewing area, that is in focus.

Elevation	Elevation is the adjustment of the scope in the vertical direction. Up and Down adjustment.

Eye Relief	This is the comfortable distance that the binocular or scope can be held from your eyes and still provide a clear sharp image. Eyeglass wearers will need a longer eye relief because the binoculars will be held against their glasses- further from their eyes. - It literally refers to the distance of the shooters eye from the eye piece on the scope.

Exit Pupil	The size of the image as seen from the binoculars' eyepiece. This is the circle of light seen in the eyepiece seen from about 10 inches away. Commonly used as a measurement of how bright the binoculars are. You can figure out the exit pupil diameter by dividing the objective lens diameter by the magnification power. (10x50mm binoculars would have a 5mm exit pupil.)

Field of View or FOV	The width of the area seen at a certain distance, usually 1000 yards. FOV stands for Field of View. What this means is how wide of an area (in ft.) that you can view at 100 yards. A higher number indicates a wider area, while a smaller number indicates a narrower area. Image courtesy of Canon

Hold Over/Under	Hold over/under is the amount of point of aim change either above or below your target, without adjusting your scope, to adjust for the trajectory of your projectile - a little similar to Kentucky Windage - Which is basically an educated or uneducated guess where your round will hit.

Illuminated Reticle	Either type of reticle can be illuminated for use in low light. Illumination is usually provided by a battery powered LED, though a radioactive element containing Tritium may be used for autonomous illumination for approximately 11 years without using a battery, via radioactive decay, like in the British SUSAT sight for the SA80 (L85) assault rifle, or the American ACOG (Advanced Combat Optical Gunsight). The light is projected forward through the scope, and reflects off the back surface of the reticle. Red is the most common color used, as it is the least destructive to the shooter's night vision, but some products use green or yellow dots, either as a single color or changeable via user selection.

Image Quality	Image quality is in a rifle scope , binocular or Cameras alike. It is crucial that the optical system of a riflescope deliver as much light as possible to the eye of the shooter. The brighter the image, the sharper the resolution, and the clearer the shot. When selecting your scope, consider brightness, clarity, resolution, power and field-of-view.

Laser Sight	An aiming device that projects a low-power laser beam on your target, where it appears as a red dot that indicates where the gun will hit. Another great high-tech accessory to make your gun look more like the ones in that Simpson & Bruckheimer movie, laser sights are actually useful in some CQB situations but more often they just alert your target with their distinctive red flare. No laser more powerful than 5mW should ever be used to point at other people, and any laser sight can damage your retina if you deliberately stare into the beam.

Light Transmission	The ratio of the total amount of light passing through the objective lens to the eye. Better levels of coating increase the amount of light reaching the eye.

Magnification	Determining the magnification of a scope, binocular and other optics can be confusing. For example if a scope is listed as a 3-9x 50 this tells the shooter that the scopes magnification is 3 times adjustable up to 9 times the magnification of the human eye's can normal vision. the "50" tells the shooter the size of the objective ( or the end facing the target) , in this case it is 50mm. An alternate term for magnification is "Power".

Mil Dot	The Mil Dot is a range estimating reticle that was developed for military applications and has taken a natural progression into Law Enforcement and other precision rifle shooting. The space between the dot centers subtend one mill radian 6(Mil). One Mil subtends 3.6" at 100yards, or 36" at 1000 yards.

Minute of Angle	Minute of Angle (MOA) is a term to designate variances on a target at 100 yards distant. Most commonly, it is used to describe the adjustment on a scope. If a scope's adjustments are listed at ј" MOA, then for every click of the adjustment knob, the bullet's point of impact will move ј" at 100 yards.

Objective	The objective is the end of the scope facing the target. The size of the objective is in direct correlation with the light gathering capability. In other words the larger the objective, the more light entering the scope which usually offers the shooter a clearer image. To determine the size of the optics objective from the description is easy. For example a 2-7x 42 refers to a 2x to 7x magnification with a 42mm objective.

Optical Coatings	Optical coatings are multiple ultra coating of a chemical film (commonly Magnesium Fluoride) to eliminated much of the reflection. The coating reduces light loss and glare, increasing light transmission and resulting in brighter, clearer images. By coating a surface with multiple films, the effect of the coating is increased, at times limiting the amount of reflected light to 0.25% to 0.5% per glass surface.

P4 Sniper Reticle	The NcStar P4 Sniper reticle is a modified version of the Mil Dot with a little of the Rangefinder reticle thrown in. Specially designed Reticle to estimate range with quickness and accuracy using a simple mathematical formula.

Parallax	A condition that occurs when the image of the target is not focused precisely on the reticle plane. Parallax is visible as an apparent movement between the reticle and the target when the shooter moves his head or, in extreme cases, as an out-of-focus image. Bushnell center-fire riflescopes under 11x are factory-set parallax-free at 100 yards; rim-fire and shotgun scopes at 50 yards. Scopes of 11x or more have a special range focus to adjust for parallax.

Plex Reticle	Standard plex Reticle gives the shooter a more natural acquisition between the Reticle and the target. If a simple crosshair style reticle with thick crosses narrowing down to medium width targeting crosshairs.

Power	The "power" of an optic is the same as the " magnification" of scopes, binoculars and all other optics. Both terms are simply express the factor to which the optic sees greater than the naked eye. For example a 2-7x 32 optic indicates that the operator is able to bring the target closer

Rangefinder Reticle	The first thing to understand about rangefinder scopes is that they all have a single magnification setting at which the reticle works. For military scopes, this is usually x10, but civilian scopes often have other settings. The rangefinder reticle is useless unless the magnification is set properly. The reticle will have measuring aids marked out on it, either in the form of hatches or bars or both, that will assist the eye in making easy size measurements. These are attuned to something that is easily found by the shooter and generally the same approximate size. Many hunting scopes with rangefinding reticles use "deer chest" increments, for example. These are scaled to the average size of a deer chest. Comparing how many hatch marks or bars the deer chest occupies at the proper magnification tells the shooter how far away the target is

Red Dot Reticle	The red dot Reticle only illumines in the center giving you a 2 moa dot for easy shot placement in virtually any light condition. Simple crosshair with center 2MOA Red Dot.

Resolution	Resolution is the measurement of an optical device's ability to produce a sharp image by distinguishing fine detail. Resolution is determined by the quality of the glass and coatings, precision manufacturing, atmospheric conditions, and visual acuity of the user.


Reticle	The reticle is common referred to as the "Crosshairs which comes from the originally reticles which are two thin wires crossed inside the scope. Reticles are on found in a wide variety of designs including but not limited to Dots, Pointed posts, Range finders, Red Dots, Small crosses, Mil-Dots, duplex, multi-Plex and many more. Short version. this the part of the scope that allows the shooter to aim at the target.

Rubber Armor Coating	Protects binoculars from minor shocks and drops while also providing the user with better grip. Also enhances weatherproofing potential.

Small Cross	Similar to the red dot Reticle, the small cross only illuminates a small portion of the Reticle for those who do not want full illumination.

Trajectory	Refers to the path the projectile (Bullet) travels from the barrel to the target. The flight of the bullet is in an Arc. The amount of the arc depends on the projectiles weight and velocity.

Turret	A Turret is the extended knobs covering the scopes windage and elevation adjustment screws. Featuring external marked increments allowing the operator to make windage and elevation adjustments without removing the turret covers. - Usually found on long distance high power optics.

Twilight Factor	Although not a term many scope users will refer too. Twilight is a measurement of the scopes efficiency at low light levels. Naturally the higher the Twilight factor of the scope the more usable it is in low light. Strangely enough the glass and coating quality is not a factor as the simply formula for Twilight factor is : The Square Root of the magnification x the diameter of the Objective lens equals the scopes Twilight Factor.

Zero	Zero is the distance that your scope is sighted in - for example if you scope is Zeroed in at 100yds - your crosshairs are set to have your bullet (projectile) hit the mark at 100yards.