RETICLES

A crosshair or reticle is a shape superimposed on an image that is used for precise alignment of a device. Crosshairs are most commonly a "+" shape, though many variations exist, including dots, posts, circles, and chevrons. Most commonly associated with telescopic sights for aiming firearms, crosshairs are also common in optical instruments used for astronomy and surveying, and are also popular in graphical user interfaces as a precision pointer. The crosshair was invented by Robert Hooke, and dates to the 17th century.

The word Reticle is from the Latin meaning "net", a network or grid of lines displayed in an optical instrument. The minimum reticle consists of simple "cross-hairs".

Telescopic sights come with a variety of different reticles, ranging from the traditional crosshairs to complex reticles designed to allow the shooter to estimate accurately the range to a target, to compensate for the bullet drop, and to compensate for the windage required due to crosswinds. A user can estimate the range to objects of known size, the size of objects at known distances, and even roughly compensate for both bullet drop and wind drifts at known ranges with a reticle-equipped scope.

For example, with a typical Leupold brand duplex 16 MOA reticle (of a type as shown in image B) on a fixed power scope, the distance from post to post (that is, between the heavy lines of the reticle spanning the center of the scope picture) is approximately 32 inches (81.3 cm) at 200 yards (183 m), or, equivalently, approximately 16 inches (40.65 cm) from the center to any post at 200 yards. With a known target of a diameter of 16 inches that fills just half the distance from scope center to post, the distance to target is approximately 400 yards (366 m). With a known target of a diameter of 16 inches that fills the entire sight picture from post to post, the range is approximately 100 yards. Other ranges can be similarly estimated accurately in an analog fashion for known target sizes through proportionality calculations. Holdover, for estimating vertical point of aim offset required for bullet drop compensation on level terrain, and horizontal windage offset (for estimating side to side point of aim offsets required for wind effect corrections) can similarly be compensated for through using approximations based on the wind speed (from observing flags or other objects) by a trained user through using the reticle marks. The less-commonly used holdunder, used for shooting on sloping terrain, can even be estimated by an appropriately-skilled user with a reticle-equipped scope, once the slope of the terrain and the slant range to target are both known.

There are two main types of reticles:

Wire reticles
Etched reticles
Wire reticles are the oldest type of reticles and are made out of metal wire. They are mounted on an optically appropriately position in the telescopic sights tube. Etched reticles are images of the desired reticle layout that are etched on an optic element. This optical element (lens) with the etched reticle is then mounted in the telescopic sights tube as an integrated part of the optics chain of the sight. When backlit through the ocular a wire reticle will reflect incoming light and not present a nice black contrasty reticle. An etched reticle will stay black if backlit. Etched reticles are by most considered to be a more refined solution and offer greater reticle lay out flexibility. Because of this some manufacturers can provide client designed custom reticles on special order. In the more expensive and high end contemporary telescopic sights etched reticles dominate the market. In cheaper telescopic sights wire reticles are still often mounted to avoid a rather specialized and costly production step.

Mil-dot reticles

If the helmeted head of a man (≈ 0.25 m tall) fits between the fourth bar and the horizontal line, the man is at approximately 100 meters distance. When the upper part of the body of a man (≈ 1 m tall) fits under the first line, he stands at approximately 400 meters distance.Modern military and law enforcement reticles are generally designed for (stadiametric) rangefinding purposes. Perhaps the most flexible ranging reticle is the "Mil-dot" reticle, which consists of duplex crosshairs with small dots at milliradian (Mil) intervals in the field of view. A milliradian equates to 3.43774677078493 MOA, that is, approximately 21.6 inches at 600 yards; each MOA equates to 1.0471975511966 inch at 100 yards, often rounded to 1 inch at 100 yards for fast mental calculations.

Users who use the metric system are better off with a Mil-dot reticle, since they do not have to hassle with the unnecessary complications of a non metric system of measurement during mental calculations. Also the Mil-dot measurements and ranging calculations are always exact in the metric system.

A trained user can pretty accurately measure the range to objects of known size, the size of objects at known distances, and compensate for both bullet drop and wind drifts at known ranges with a Mil-dot reticle-equipped scope. This is what a Netherlands Army sniper sees through his Schmidt & Bender 3-12x50 PM II[1] telescopic sight. The Mil-dots can be seen on the cross hairs. By means of a mathematical formula - (size target / number of mil of dots) x 1000 = distance - the user can measure the range to a target. An object of 1 meter tall is exactly 1 Mil tall at 1000 meters distance. If the user sees an object of 1.8 m tall for example as three mil dots tall through the riflescope the object is at 600 m distance - (1.8 / 3) * 1000 = 600.

The four horizontal bars over the horizontal line are also intended for (quick) ranging purposes