Editing Reticle (section)

==Uses==

===Firearms===

Telescopic sights for firearms, generally just called ''scopes'', are probably the device most often associated with crosshairs. [[Motion picture]]s 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 cross-hair 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 cross-hair in modern scopes are variants on the ''duplex'' cross-hair, 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. The thin bars in a duplex reticle may also be designed to be used as a measure. Called a 30/30 reticle, the thin bars on such a reticle span 30 minutes of arc (0.5º), which is approximately equal to 30 inches at 100 yards or 90 centimeters at 100 meters. This enables an experienced shooter to deduce, on the basis of the known size of an object in view, (as opposed to guess or estimate) the range within an acceptable error limit.

====Wire crosshairs====
[[File:Findot reticle.svg|thumb|right|Etched "FinnDot" reticle (a regular [[milliradian|mil]]-dot reticle with the addition of 400 m – 1200 m holdover [[stadiametric rangefinding|(stadiametric) rangefinding]] brackets for 1 meter high or 0.5 meter wide targets at 400, 600, 800, 1000 and 1200 m). Reticle illumination is provided by a tritium ampoule embedded in the elevation turret.]]

Originally crosshairs were constructed out of hair or spiderweb, these materials being sufficiently 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 flattening 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====
[[Image:USGsight01.jpg|thumb |alt=The day and low-light reticles of the USG reflex sight used on the FN P90 / PS90 USG models |The day and low-light reticles of the integral [[reflex sight]] used on the [[FN P90]] / PS90 USG models]]

The first suggestion for etched glass reticles was made by [[Philippe de La Hire]] in 1700.<ref name="daumas">Maurice Daumas, ''Scientific Instruments of the Seventeenth and Eighteenth Centuries and Their Makers'', Portman Books, London 1989  {{ISBN|978-0-7134-0727-3}}</ref> His method was based on engraving the lines on a glass plate with a [[diamond]] point. Many modern crosshairs are actually [[Industrial etching|etch]]ed 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 [[Stadiametric rangefinding|range estimation]] and bullet drop and drift compensation (see [[external ballistics]]). A potential disadvantage of glass reticles is that the surface of the glass reflects some light (about 4% per surface on uncoated glass<ref>Richard Feynman, the red books</ref>) lessening transmission through the scope, although this light loss is near zero if the glass is multicoated (coating being the norm for all modern high quality optical products).

====Illuminated reticles====
Reticles may be illuminated, either by a plastic or [[fiber optic]] [[light pipe]] collecting ambient light or, in low light conditions, by a [[battery (electricity)|battery]] powered [[LED]]. Some sights also use the radioactive decay of [[tritium]] for illumination that can work for 11 years without using a battery, used in the British [[SUSAT]] sight for the [[SA80]] (L85) assault rifle and in the American [[Advanced Combat Optical Gunsight|ACOG (Advanced Combat Optical Gunsight)]]. 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 illumination, either as a single colour or changeable via user selection.

====Graticule====
Another term for reticle is ''graticule'', which is frequently encountered in British and British military technical manuals. It came into common use during [[World War I]].<ref>[https://archive.org/stream/dictionaryofappl00glazmiss#page/120/mode/2up Glazebrook, Sir Richard, A Dictionary of Applied Physics, Macmillan and Co., London, 1923.]</ref>

===Reticle focal plane===
The reticle may be located at the front or rear focal plane (First Focal Plane (FFP) or Second Focal Plane (SFP))<ref>{{cite web|url=https://accurateordnance.com/first-vs-second-focal-plane/ |title=First vs Second Focal Plane – What is the Differences?|date=25 July 2022 }}</ref> of the telescopic sight. On fixed power telescopic sights there is no significant difference, but on variable power telescopic sights 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 focal plane reticles are slightly more durable, but most American users prefer that the reticle remains constant as the image changes size, so nearly all modern American variable power telescopic sights are rear focal plane designs.{{citation needed|date=May 2019}} American and European high end optics manufacturers often leave the customer the choice between a FFP or SFP mounted reticle.

====Collimated reticles====
[[File:Reflector reflex sight diagram 3.png|thumb|right|Diagram of three types of reflector sights that produce collimated reticles. The top uses a collimating lens (CL) and a beam splitter (B) to create a [[virtual image]] at infinity (V) of a reticle (R). The bottom two use half silvered curved mirrors (CM) as the collimating optics with the reticle off-set or between the mirror and the observer.]]
{{main|Reflector sight}}
Collimated reticles are produced by non-magnifying optical devices such as [[reflector sight]]s (often called ''reflex sights'') that give the viewer an image of the reticle superimposed over the field of view, and blind [[collimator sight]]s that are used with both eyes. Collimated reticles are created using [[refraction|refractive]] or [[reflection (physics)|reflective]] [[Collimator#Optical collimators|optical collimators]] to generate a [[Collimated light|collimated]] image of an illuminated or reflective reticle. These types of sights are used on surveying/triangulating equipment, to aid celestial telescope aiming, and as [[gunsights|sight]]s on [[firearm]]s.  Historically they were used on larger military weapon systems that could supply an electrical source to illuminate them and 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). More recently sights using low power consumption durable [[light emitting diode]]s as the reticle (called ''[[red dot sight]]''s) have become common on small arms with versions like the [[Aimpoint CompM2]] being widely fielded by the U.S. Military.

====Holographic reticles====
[[Holographic weapon sight]]s use a [[hologram|holographic]] image of a reticle at finite set range built into the viewing window and a [[collimated light|collimated]] [[laser diode]] to illuminate it.  An advantage to holographic sights is that they eliminate a type of [[parallax]] problem found in some optical collimator based sights (such as the [[red dot sight]]) where the spherical mirror used induces [[spherical aberration]] that can cause the reticle to skew off the sight's [[optical axis]]. The use of a hologram also eliminates the need for image dimming narrow band reflective coatings and allows for reticles of almost any shape or [[milliradian|mil]] size. A downside to the holographic weapon sight can be the weight and shorter battery life. As with red dot sights, holographic weapon sights have also become common on small arms with versions like the [[EOTech|Eotech]] 512.A65 and similar models fielded by the U.S. Military<ref>{{cite web |url=http://www.defenseindustrydaily.com/Holographic-Sights-for-SOCOM-M4s-06416/ |title=Holographic Sights for SOCOM M4s |access-date=30 August 2012}}</ref>  and various law enforcement agencies.

===Surveying and astronomy===
In older instruments, reticle crosshairs and stadia marks were made using threads taken from the [[Pupa#Cocoon|cocoon]] of the [[brown recluse spider]]. This very fine, strong spider silk makes for an excellent crosshair.<ref>Raymond Davis, Francis Foote, Joe Kelly, ''Surveying, Theory and Practice'', McGraw-Hill Book Company, 1966 LC 64-66263</ref><ref>Berenbaum, May R., ''Field Notes - Spin Control'', The Sciences, The New York Academy Of Sciences, September/October 1995</ref>

====Surveying====
In surveying, reticles are designed for specific uses. [[Dumpy level|Level]]s and [[theodolite]]s would have slightly different reticles. However, both may have features such as [[stadia mark]]s 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 sight]]s are popular, often in conjunction with a small telescope with a crosshair reticle. They make aiming the telescope at an [[astronomical object]] easier.

The constellation [[Reticulum]] was designated to recognize the reticle and its contributions to astronomy.