reticle n : a network of fine lines, dots, cross hairs, or wires in the focal plane of the eyepiece of an optical instrument [syn: reticule, graticule]

English

Etymology

From later Latin reticulum, diminutive of rete ‘net’.

Pronunciation

• /'rɛtɪkəl/

Noun

1. a small net
2. a gridwork or lattice of lines set into the eyepiece of optical instruments to help with measurements or observation

Translations

Derived terms

• have somebody or something in one's reticle - to be targeting somebody or something

See also

• Reticulum
• reticule

For the fictional characters named Crosshairs see Crosshairs (Transformers).

A crosshair or reticle is a shape superimposed on an image that is used for precise alignment of a device. Crosshairs are most commonly represented as intersecting lines in a "+" shape, though many variations exist, including dots, posts, circles, scales, chevrons, or a combination of each. 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", as described above.

Use in firearms

Telescopic sights for firearms, generally just called scopes, are probably the device most often associated with crosshairs. Motion pictures and the media often use a view through crosshairs as a dramatic device, which has given crosshairs wide cultural exposure.

Reticle shape

While the traditional thin crossing lines are the original and still the most familiar crosshair shape, they are really best suited for precision aiming at high contrast targets, as the thin lines are easily lost in complex backgrounds, such as those encountered while hunting. Thicker bars are much easier to discern against a complex background, but lack the precision of thin bars. The most popular types of crosshair in modern scopes are variants on the duplex crosshair, with bars that are thick on the perimeter and thin out in the middle. The thick bars allow the eye to quickly locate the center of the reticle, and the thin lines in the center allow for precision aiming.

Wire crosshairs

The original crosshairs in fact used hair, as it was thin and strong. Many modern scopes use wire crosshairs, which can be flattened to various degrees to change the width. These wires are usually silver in color, but appear black when backlit by the image passing through the scope's optics. Wire reticles are by nature fairly simple, as they require lines that pass all the way across the reticle, and the shapes are limited to the variations in thickness allowed by flatting the wire; duplex crosshairs, and crosshairs with dots are possible, and multiple horizontal or vertical lines may be used. The advantage of wire crosshairs is that they are fairly tough and durable, and provide no obstruction to light passing through the scope.

Etched reticles

The first suggestion for etched glass reticles was made by Philippe de La Hire in 1700. His method was based on engraving the lines on a glass plate with a diamond point. Many modern crosshairs are actually etched onto a thin plate of glass, which allows a far greater latitude in shapes. Etched glass reticles can have floating elements, which do not cross the reticle; circles and dots are common, and some types of glass reticles have complex sections designed for use in range estimation and bullet drop and drift compensation (see external ballistics). The disadvantage of glass reticles is that they are less durable than wire crosshairs, and the surface of the glass reflects some light, lessening transmission through the scope.

Illuminated reticles

Either type of reticle can be illuminated for use in low light. Illumination is usually provided by a battery powered LED, though other sources can be used. 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.

Focal plane

The reticle may be located at the front or rear focal plane of the scope. On fixed power scopes there is no significant difference, but on variable power scopes the front plane reticle remains at a constant size compared to the target, while rear plane reticles remain a constant size to the user as the target image grows and shrinks. Front plane reticles are slightly more durable, but most users prefer that the reticle remain constant as the image changes size, so nearly all modern variable power scopes are rear focal plane designs.

Collimated reticles

Collimated reticles are usually used in sights that have no magnification. Instead it gives the viewer an image of the reticle superimposed over the field of view at infinity with no parallax that is aligned with the device to which it is attached. Collimated reticles are created using refractive or reflective optical collimators to generate a collimated image of an illuminated or reflective reticle. The most common types use beam splitters to allow the viewer to see the field of view and a reflection of the projected reticle simultaneously. These types, sometimes called reflex sights, are used on surveying/triangulating equipment, consumer telescope aiming devices, and (historically) on military weapons where the operator needed a wide field of view to track and range a moving target visually (i.e. weapons from the pre laser/radar/computer era). A popular weapons reflex sight still in use today is the Red dot sight.

Holographic reticles

Bushnell has recently introduced the Holosight, which is similar to a red dot sight, but using a holographic reticle and a laser diode for illumination. The Holosight is able to render a 3-D reticle image. The downside to the Holosight is the cost and weight; it is more expensive and significantly heavier than most red dot sights, which are its nearest competition.

Use in Surveying and Astronomy

In older instruments, reticle crosshairs and stadia marks were made using threads taken from the cocoon of the brown recluse spider. This very fine, strong spider silk makes for an excellent crosshair.

Surveying

In surveying, reticles are designed for specific uses. Levels and theodolites would have slightly different reticles. However, both may have features such as stadia marks to allow distance measurements.

Astronomy

For astronomical uses, reticles could be simple crosshair designs or more elaborate designs for special purposes. Telescopes used for polar alignment could have a reticle that indicates the position of Polaris relative to the north celestial pole. Telescopes that are used for very precise measurements would have a filar micrometer as a reticle; this could be adjusted by the operator to measure angular distances between stars.

For aiming telescopes, reflex sights are popular, often in conjunction with a small telescope with a crosshair reticle. The reflex sight, such as the Telrad, make aiming the telescope on a Astronomical object or a region of the sky quite easy.

References

External links

• A list of firearm scope reticle styles offered by various manufacturers
• Chuck Hawks' article on firearm scope reticles
• A firearm scope with a Christmas tree type reticle
• An explanation of firearm rangefinding reticles from a maker of ballistics software
• Article on Cabela's Alaskan Guide scopes, which use a first focal plane reticle
• User Guide for Mil-Dot Equipped Optics, Remington Military Products Division
• MILS and MOA - A Comprehensive Manual to Understanding: types of "Mils", types of Minute of Angle (moa), the Derivation of The Range Estimation Equations by Robert J. Simeone

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