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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Reticle | 2/2 | https://en.wikipedia.org/wiki/Reticle | reference | science, encyclopedia | 2026-05-05T09:41:55.447970+00:00 | kb-cron |
=== Reticle focal plane === The reticle may be located at the front or rear focal plane (First Focal Plane (FFP) or Second Focal Plane (SFP)) 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. American and European high end optics manufacturers often leave the customer the choice between a FFP or SFP mounted reticle.
==== Collimated reticles ====
Collimated reticles are produced by non-magnifying optical devices such as reflector sights (often called reflex sights) that give the viewer an image of the reticle superimposed over the field of view, and blind collimator sights that are used with both eyes. Collimated reticles are created using refractive or reflective optical collimators to generate a 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 sights on firearms. 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 diodes as the reticle (called red dot sights) have become common on small arms with versions like the Aimpoint CompM2 being widely fielded by the U.S. Military.
==== Holographic reticles ==== Holographic weapon sights use a holographic image of a reticle at finite set range built into the viewing window and a 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 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 512.A65 and similar models fielded by the U.S. Military and various law enforcement agencies.
=== 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. They make aiming the telescope at an astronomical object easier. The constellation Reticulum was designated to recognize the reticle and its contributions to astronomy.
== See also == Adrien Auzout Deflection (ballistics) Focusing screen – used in photography, and often etched Iron sight List of astronomical instruments Ocular micrometer Photomask – partial plate with holes or transparencies used in photolithography integrated circuit fabrication is also called a "reticle" Sniper Target blip Parallax
== References ==
== External links ==
Reticles