A designated marksman ( DM ), squad advanced marksman ( AD ) or squad designated marksman ( SDM ) is a military marksman role in an infantry squad . The term sniper was used in Soviet doctrine although the soldiers using the Dragunov SVD were the first to use a specifically designed designated marksman rifle .
153-667: The DM's role is to supplement the attached squad by providing accurate fire upon enemy targets at distances up to 600 metres (660 yd). Due to the need for repeated effective fire, the DM is usually equipped with a scoped semi-automatic rifle called a designated marksman rifle (DMR). Like snipers , DMs are trained in scouting and precise shooting, but unlike the more specialized "true" sniper (who often operate independently), they operate as an intrinsic part of an infantry fireteam and are tasked to lay down accurate support fire at valuable targets as per tactical necessity, thus extending
306-442: A reticle – mounted in a focally appropriate position in its optical system to provide an accurate point of aim. Telescopic sights are used with all types of systems that require magnification in addition to reliable visual aiming, as opposed to non-magnifying iron sights , reflector (reflex) sights , holographic sights or laser sights , and are most commonly found on long-barrel firearms , particularly rifles, usually via
459-579: A Ghillie suit ), a DM will tactically move with his unit and is otherwise equipped in the same way as other members of the infantry platoon. The designated marksman is intended to fill the gap between the typical infantry rifle and longer-range sniper rifles. The typical service rifle is intended for use at ranges up to a maximum of 300 meters, while sniper rifles are generally optimized for ranges of 600 meters and greater. Designated marksman rifles are designed to fill this gap, typically being employed at ranges of 300–600 metres (330–660 yd). In some cases,
612-408: A White-tailed deer buck by adjusting magnification until the area between the backbone and the brisket fits between the crosshairs and the top thick post of the reticle. Once that is done, the range be read from the scale printed on the magnification adjustment ring. Although FFP designs are not susceptible to magnification-induced errors, they have their own disadvantages. It's challenging to design
765-500: A mathematical formula "[Target size] ÷ [Number of mil intervals] × 1000 = Distance", the user can easily calculate the distance to a target, as a 1-meter object is going to be exactly 1 milliradian at a 1000-meter distance. For example, if the user sees an object known to be 1.8 meters tall as something 3 mils tall through the telescopic sight, the distance to that object will be 600 meters (1.8 ÷ 3 × 1000 = 600). Some milling reticles have additional marking patterns in
918-491: A scope mount . Similar devices are also found on other platforms such as artillery , tanks and even aircraft . The optical components may be combined with optoelectronics to add night vision or smart device features. The first experiments directed to give shooters optical aiming aids go back to the early 17th century. For centuries, different optical aiming aids and primitive predecessors of telescopic sights were created that had practical or performance limitations. In
1071-450: A zoom mechanism behind the erector lenses . Variable-power sights offer more flexibility when shooting at varying distances, target sizes and light conditions, and offer a relative wide field of view at lower magnification settings. The syntax for variable sights is the following: minimal magnification – maximum magnification × objective lens , for example "3-9×40" means a telescopic sight with variable magnification between 3× and 9×, and
1224-416: A 40 mm objective lens. The ratio between the maximum and minimum magnifications of a variable-power sight is known as its "zoom ratio". Confusingly, some older telescopic sights, mainly of German or other European manufacture, have a different classification where the second part of the designation refers to light-gathering power. In these cases, a 4×81 (4× magnification) sight would be presumed to have
1377-436: A background that is brighter than an animal's body or military vehicle; it is a form of active camouflage. It is notably used by some species of squid , such as the firefly squid and the midwater squid . The latter has light-producing organs ( photophores ) scattered all over its underside; these create a sparkling glow that prevents the animal from appearing as a dark shape when seen from below. Counterillumination camouflage
1530-429: A brighter sight picture than a 2.5×70 (2.5× magnification), but the objective lens diameter would not bear any direct relation to picture brightness, as brightness is affected also by the magnification factor. Typically objective lenses on early sights are smaller than modern sights, in these examples the 4×81 would have an objective 36 mm diameter and the 2.5×70 should be approximately 21 mm (relative luminosity
1683-429: A clear evolutionary advantage in plants: they would tend to escape from being eaten by herbivores . Another possibility is that some plants have leaves differently coloured on upper and lower surfaces or on parts such as veins and stalks to make green-camouflaged insects conspicuous, and thus benefit the plants by favouring the removal of herbivores by carnivores. These hypotheses are testable. Some animals, such as
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#17327807245461836-445: A combination of the above, that are added to a crosshair to help with easier aiming. Many modern reticles are designed for (stadiametric) rangefinding purposes. Perhaps the most popular and well-known ranging reticle is the mil-dot reticle , which consists of a duplex crosshair with small dots marking each milliradian (or "mil") intervals from the center. An alternative variant uses perpendicular hash lines instead of dots, and
1989-403: A combination of the two. Most forms of camouflage are ineffective when the camouflaged animal or object moves, because the motion is easily seen by the observing predator, prey or enemy. However, insects such as hoverflies and dragonflies use motion camouflage : the hoverflies to approach possible mates, and the dragonflies to approach rivals when defending territories. Motion camouflage
2142-405: A complex production process. The main tube of telescopic sights varies in size, material, the applied production process and surface finish. The typical outside diameters vary between 19.05 mm (0.75 in) and 40 mm (1.57 in), although 25.4 mm (1 in), 30 mm and recently 34 mm are by far the most common sizes. The internal diameter of the main tube influences
2295-662: A crisp tactile feedback corresponding to each graduation of turn, often accompanied by a soft but audible clicking sound. Each indexing increment is thus colloquially called a "click", and the corresponding angular adjustment of the optical axis is known as the click value . The most commonly seen click values are 1 ⁄ 4 MOA (often expressed in approximations as " 1 ⁄ 4 inch at 100 yards") and 0.1 mil (often expressed as "10 mm at 100 meters"), although other click values such as 1 ⁄ 2 MOA, 1 ⁄ 3 MOA or 1 ⁄ 8 MOA and other mil increments are also present on
2448-445: A first focal plane reticle expands and shrinks along with the rest of the image as the magnification is adjusted, while a second focal plane reticle would appear the same size and shape to the user as the target image grows and shrinks. In general, the majority of modern variable-power sights are SFP unless stated otherwise. Every European high-end telescopic sight manufacturer offers FFP reticles on variable power telescopic sights, since
2601-442: A fish can be seen by a factor of 6 compared to a fish with a nominal 2% reflectance. Species with this adaptation are widely dispersed in various orders of the phylogenetic tree of bony fishes ( Actinopterygii ), implying that natural selection has driven the convergent evolution of ultra-blackness camouflage independently many times. In mimesis (also called masquerade ), the camouflaged object looks like something else which
2754-470: A fixed magnification factor of 10×, with a 50 mm objective lens. In general terms, larger objective lens diameters, due to their ability to gather a higher luminous flux , provide a larger exit pupil and hence provide a brighter image at the eyepiece . Most early telescopic sights were fixed-power and were in essence specially designed viewing telescopes. Telescopic sights with variable magnifications appeared later, and were varied by manually adjusting
2907-430: A gap in the firepower of the rifle platoon that a more accurate optic-equipped service rifle derivative can usefully fulfill, especially in theaters such as Afghanistan where the shortcomings of standard 5.56mm service rifles at ranges over 300 meters became apparent. The DM role differs significantly from that of a specially trained sniper . A sniper is a specialist highly trained in fieldcraft, who carries out
3060-567: A general resemblance to the background, high contrast disruptive coloration , eliminating shadow, and countershading . In the open ocean, where there is no background, the principal methods of camouflage are transparencying, silveringing, and countershading, while the ability to produce light is among other things used for counter-illumination on the undersides of cephalopods such as squid . Some animals, such as chameleons and octopuses , are capable of actively changing their skin pattern and colors , whether for camouflage or for signalling. It
3213-475: A high contrast pattern that could be disruptive coloration, the adults are very conspicuous when in the open. Some authors have argued that adult giraffes are cryptic, since when standing among trees and bushes they are hard to see at even a few metres' distance. However, adult giraffes move about to gain the best view of an approaching predator, relying on their size and ability to defend themselves, even from lions, rather than on camouflage. A different explanation
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#17327807245463366-673: A light source to provide an illuminated reticle for low-light condition aiming. In sights such as the SUSAT or Elcan C79 Optical Sight tritium-illuminated reticles are used. The Trijicon Corporation, famous for their ACOG prism sights that are adopted by various assault infantry branches of the United States military , uses tritium in their combat and hunting-grade firearm optics. The tritium light source has to be replaced every 8–12 years, since it gradually loses brightness due to radioactive decay . Camouflage Camouflage
3519-682: A locally manufactured licensed variant of the SVD Dragunov in the Designated Marksman role. The Dragunov is used in conjunction with the INSAS family of weapons to give flexibility and striking power, in short to mid range firefights, to Indian Army infantry units engaged with opposing forces. The Israel Defense Forces (IDF) implemented significant changes to sharpshooting doctrine in the 1990s. Doctrine, training program, and courseware were completely rewritten and snipers were issued
3672-584: A long-eye relief (LER) telescopic sight is the German ZF41 which was used during World War II on Karabiner 98k rifles. An early example of a man-portable sight for low visibility/night use is the Zielgerät (aiming device) 1229 (ZG 1229), also known by its code name Vampir ("vampire"). The ZG 1229 Vampir was a Generation 0 active infrared night vision device developed for the Wehrmacht for
3825-519: A mirror oriented vertically makes animals such as fish invisible from the side. Most fish in the upper ocean such as sardine and herring are camouflaged by silvering. The marine hatchetfish is extremely flattened laterally, leaving the body just millimetres thick, and the body is so silvery as to resemble aluminium foil . The mirrors consist of microscopic structures similar to those used to provide structural coloration : stacks of between 5 and 10 crystals of guanine spaced about 1 ⁄ 4 of
3978-745: A modified M16, which was accurized in a manner similar to the U.S. Marines SAM-R, unofficially designated the AMU Squad Designated Marksman Rifle (SDM-R). This rifle was designed for engagements up to 1000m. The U.S. Army DM also uses the predecessor of the M16 rifle, the M14, in certain infantry line units. These are commonly equipped with Leupold optics, a Sage stock and are designated the M14SE Crazy Horse . The United States Navy SEAL Teams employs SDM rifles in roughly
4131-404: A particularly black skin which reflected only 0.044% of 480 nm wavelength light. The ultra-blackness is achieved with a thin but continuous layer of particles in the dermis , melanosomes . These particles both absorb most of the light, and are sized and shaped so as to scatter rather than reflect most of the rest. Modelling suggests that this camouflage should reduce the distance at which such
4284-411: A period of about 8000 years the single agouti gene developed 9 mutations that each made expression of yellow fur stronger under natural selection, and largely eliminated melanin-coding black fur coloration. On the other hand, all black domesticated cats have deletions of the agouti gene that prevent its expression, meaning no yellow or red color is produced. The evolution, history and widespread scope of
4437-502: A predator blends in with the background, enabling it to approach prey). His experiments showed that swallow-tailed moth pupae were camouflaged to match the backgrounds on which they were reared as larvae . Poulton's "general protective resemblance" was at that time considered to be the main method of camouflage, as when Frank Evers Beddard wrote in 1892 that "tree-frequenting animals are often green in colour. Among vertebrates numerous species of parrots , iguanas , tree-frogs , and
4590-439: A range of ISTAR -specific missions independent of others, and more specialized than standard infantry tasks. In contrast, a DM is a soldier who has received additional marksmanship training. Within a fireteam , the DM's role is to provide an additional capability to the infantry platoon, which is the ability to engage targets at greater ranges than the other members of the squad or section. The DM operates as an integral member of
4743-409: A reason, such as to lure prey. For example, the nematocysts (stinging cells) of the transparent siphonophore Agalma okenii resemble small copepods . Examples of transparent marine animals include a wide variety of larvae , including radiata (coelenterates), siphonophores, salps (floating tunicates ), gastropod molluscs , polychaete worms, many shrimplike crustaceans , and fish; whereas
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4896-693: A reproductive advantage, enabling them to leave more offspring, on average, than other members of the same species . In his Origin of Species , Darwin wrote: When we see leaf-eating insects green, and bark-feeders mottled-grey; the alpine ptarmigan white in winter, the red-grouse the colour of heather , and the black-grouse that of peaty earth, we must believe that these tints are of service to these birds and insects in preserving them from danger. Grouse, if not destroyed at some period of their lives, would increase in countless numbers; they are known to suffer largely from birds of prey ; and hawks are guided by eyesight to their prey, so much so, that on parts of
5049-474: A reticle that is visible through the entire range of magnification: a reticle that looks fine and crisp at 24× magnification may be very difficult to see at 6×. On the other hand, a reticle that is easy to see at 6× may be too thick at 24× to make precision shots. Shooting in low light conditions also tends to require either illumination or a bold reticle, along with lower magnification to maximize light gathering. In practice, these issues tend to significantly reduce
5202-483: A round already used in the infantry battalion, such as 5.56×45mm or 7.62×51mm, and it will retain semi-automatic firing capability with a magazine capacity of 10, 20, or 30 rounds, depending on the firearm in question. Designated marksmen will carry whichever service pistol is specified in their unit's TOE for their billet or Military Occupational Specialty (MOS), if one is specified or available at all. A typical Australian Army fireteam of four soldiers will include
5355-703: A round dot, small cross , diamond , chevron and/or circle in the center (in some prism sights and reflex / holographic sights ), or a pointed vertical bar in a " T "-like pattern (such as the famous "German #1" reticle used on the Wehrmacht ZF41 sights during the Second World War , or the SVD -pattern reticle used on the Soviet PSO-1 sights during the Cold War ) that essentially imitates
5508-562: A scout employing an F88S Austeyr (5.56 NATO) fitted with an enhanced optic device, usually either an ACOG or ELCAN C79 . Additionally, 7.62 mm marksman rifles ( SR-25s ) are employed by the maneuver support teams in the platoon. However, HK417 rifles have been procured by the Army as a substitute for the F88S during operations in Afghanistan and possibly thereafter. The SASR also uses
5661-595: A sight made by gunsmith Morgan James of Utica, New York . Chapman worked with James on the concepts and design of the Chapman-James sight. In 1855, optician William Malcolm of Syracuse, New York began producing his own telescopic sight, used an original design incorporating achromatic lenses such as those used in telescopes, and improved the windage and elevation adjustments. These Malcolm sights were between 3× and 20× magnification (possibly more). Malcolm's sights and those made by Vermont jeweller L. M. Amidon were
5814-505: A small elastic sac, which can be stretched or allowed to relax under the control of the brain to vary its opacity. By controlling chromatophores of different colours, cephalopods can rapidly change their skin patterns and colours. On a longer timescale, animals like the Arctic hare , Arctic fox , stoat , and rock ptarmigan have snow camouflage , changing their coat colour (by moulting and growing new fur or feathers) from brown or grey in
5967-416: A species of nudibranch that feeds on stony coral , utilizes specific cryptic patterning in reef ecosystems. The nudibranch syphons pigments from the consumed coral into the epidermis, adopting the same shade as the consumed coral. This allows the nudibranch to change colour (mostly between black and orange) depending on the coral system that it inhabits. However, P. melanocrachia can only feed and lay eggs on
6120-781: A target of a known diameter of 16 inches fills just half of the total post-to-post distance (i.e. filling from sight center to post), then the distance to target is approximately 200 yards (180 m). With a 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
6273-518: A telescope to a rifle as a sighting aid, but was unable to mount it sufficiently far forward to prevent the eyepiece impacting with the operator's eye during recoil . In the same year, James Lind and Captain Alexander Blair described a gun which included a telescopic sight. The first rifle sight was created in 1835 -1840. In the book The Improved American Rifle , written in 1844, British-American civil engineer John R. Chapman described
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6426-417: A typical Leupold brand 16 minute of angle (MOA) duplex reticle (similar to image B) on a fixed-power telescopic sight, the distance from post to post, between the heavier lines of the reticle spanning the center of the sight picture, is approximately 32 inches (810 millimeters) at 200 yards (180 m), or, equivalently, approximately 16 inches (410 millimeters) from the center to any post at 200 yards. If
6579-409: A wavelength apart to interfere constructively and achieve nearly 100 per cent reflection. In the deep waters that the hatchetfish lives in, only blue light with a wavelength of 500 nanometres percolates down and needs to be reflected, so mirrors 125 nanometres apart provide good camouflage. In fish such as the herring which live in shallower water, the mirrors must reflect a mixture of wavelengths, and
6732-452: Is acellular and highly transparent. This conveniently makes them buoyant , but it also makes them large for their muscle mass, so they cannot swim fast, making this form of camouflage a costly trade-off with mobility. Gelatinous planktonic animals are between 50 and 90 percent transparent. A transparency of 50 percent is enough to make an animal invisible to a predator such as cod at a depth of 650 metres (2,130 ft); better transparency
6885-475: Is achieved by moving so as to stay on a straight line between the target and a fixed point in the landscape; the pursuer thus appears not to move, but only to loom larger in the target's field of vision. Some insects sway while moving to appear to be blown back and forth by the breeze. The same method can be used for military purposes, for example by missiles to minimise their risk of detection by an enemy. However, missile engineers, and animals such as bats, use
7038-433: Is an important component of camouflage in all environments. For instance, tree-dwelling parakeets are mainly green; woodcocks of the forest floor are brown and speckled; reedbed bitterns are streaked brown and buff; in each case the animal's coloration matches the hues of its habitat. Similarly, desert animals are almost all desert coloured in tones of sand, buff, ochre, and brownish grey, whether they are mammals like
7191-436: Is argued that these juvenile giraffes must be very well camouflaged; this is supported by coat markings being strongly inherited . The possibility of camouflage in plants was little studied until the late 20th century. Leaf variegation with white spots may serve as camouflage in forest understory plants, where there is a dappled background; leaf mottling is correlated with closed habitats. Disruptive camouflage would have
7344-418: Is common in military usage, both for uniforms and for military vehicles. Disruptive patterning, however, does not always achieve crypsis on its own, as an animal or a military target may be given away by factors like shape, shine, and shadow. The presence of bold skin markings does not in itself prove that an animal relies on camouflage, as that depends on its behaviour. For example, although giraffes have
7497-409: Is essential that its brightness can be adjusted. A reticle that is too bright will cause glare in the operator's eye, interfering with their ability to see in low-light conditions. This is because the pupil of the human eye closes quickly upon receiving any source of light. Most illuminated reticles provide adjustable brightness settings to adjust the reticle precisely to the ambient light. Illumination
7650-406: Is etched onto one of the prism's internal reflection surfaces, which allows an easy way to illuminate the reticle (from the back side of the prism) even when active illumination is turned off. Being optical telescopes , prism sights can focally compensate for a user's astigmatism . Prismatic sights are lighter and more compact than conventional telescopic sights, but are mostly fixed-powered in
7803-435: Is fossil evidence of camouflaged insects going back over 100 million years, for example lacewings larvae that stick debris all over their bodies much as their modern descendants do, hiding them from their prey. Dinosaurs appear to have been camouflaged, as a 120 million year old fossil of a Psittacosaurus has been preserved with countershading . Camouflage does not have a single genetic origin. However, studying
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#17327807245467956-403: Is implied by young giraffes being far more vulnerable to predation than adults. More than half of all giraffe calves die within a year, and giraffe mothers hide their newly born calves, which spend much of the time lying down in cover while their mothers are away feeding. The mothers return once a day to feed their calves with milk. Since the presence of a mother nearby does not affect survival, it
8109-465: Is known as the mil-hash reticle . Such graduated reticles, along with those with MOA -based increments, are collectively and unofficially called " milling reticles ", and have gained significant acceptance in NATO and other military and law enforcement organizations. Mil-based reticles, being decimal in graduations, are by far more prevalent due to the ease and reliability of ranging calculations with
8262-525: Is less often used for military camouflage, despite Second World War experiments that showed its effectiveness. English zoologist Hugh Cott encouraged the use of methods including countershading, but despite his authority on the subject, failed to persuade the British authorities. Soldiers often wrongly viewed camouflage netting as a kind of invisibility cloak, and they had to be taught to look at camouflage practically, from an enemy observer's viewpoint. At
8415-434: Is mediated by a type of chromatophore known as melanophores that contain dark pigment. A melanophore is star-shaped; it contains many small pigmented organelles which can be dispersed throughout the cell, or aggregated near its centre. When the pigmented organelles are dispersed, the cell makes a patch of the animal's skin appear dark; when they are aggregated, most of the cell, and the animal's skin, appears light. In frogs,
8568-540: Is not every reason to believe it the very best conceivable device for the concealment of its wearer", and using paintings such as Peacock in the Woods (1907) to reinforce his argument. Thayer was roundly mocked for these views by critics including Teddy Roosevelt . The English zoologist Hugh Cott 's 1940 book Adaptive Coloration in Animals corrected Thayer's errors, sometimes sharply: "Thus we find Thayer straining
8721-739: Is possible that some plants use camouflage to evade being eaten by herbivores . Military camouflage was spurred by the increasing range and accuracy of firearms in the 19th century. In particular the replacement of the inaccurate musket with the rifle made personal concealment in battle a survival skill. In the 20th century, military camouflage developed rapidly, especially during the First World War . On land, artists such as André Mare designed camouflage schemes and observation posts disguised as trees. At sea , merchant ships and troop carriers were painted in dazzle patterns that were highly visible, but designed to confuse enemy submarines as to
8874-463: Is required for invisibility in shallower water, where the light is brighter and predators can see better. For example, a cod can see prey that are 98 percent transparent in optimal lighting in shallow water. Therefore, sufficient transparency for camouflage is more easily achieved in deeper waters. Some tissues such as muscles can be made transparent, provided either they are very thin or organised as regular layers or fibrils that are small compared to
9027-675: Is that admirable secret, which, as all other things, appeared when it pleased the All Disposer, at whose direction a spider's line drawn in an opened case could first give me by its perfect apparition, when I was with two convexes trying experiments about the sun, the unexpected knowledge...if I .... placed a thread where that glass [the eyepiece] would best discern it, and then joining both glasses, and fitting their distance for any object, I should see this at any part that I did direct it to ..." — William Gascoigne In 1776, Charles Willson Peale collaborated with David Rittenhouse to mount
9180-483: Is the likely function of the bioluminescence of many marine organisms, though light is also produced to attract or to detect prey and for signalling. Counterillumination has rarely been used for military purposes. " Diffused lighting camouflage " was trialled by Canada's National Research Council during the Second World War. It involved projecting light on to the sides of ships to match the faint glow of
9333-470: Is the square of the exit pupil as measured in mm; a 36 mm objective lens diameter divided by the 4× magnification gives an exit pupil of 9 mm; 9×9=81) A relatively new type of telescopic sight, called prismatic telescopic sight , prismatic sight or " prism scope ", replaces the image-erecting relay lenses of a traditional telescope with a roof prism design commonly found in compact binoculars , monoculars and spotting scopes . The reticle
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#17327807245469486-513: Is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard 's spotted coat, the battledress of a modern soldier , and the leaf-mimic katydid 's wings. A third approach, motion dazzle, confuses the observer with a conspicuous pattern, making the object visible but momentarily harder to locate. The majority of camouflage methods aim for crypsis, often through
9639-428: Is their mutual resemblance." He also explained the coloration of sea fish such as the mackerel : "Among pelagic fish it is common to find the upper surface dark-coloured and the lower surface white, so that the animal is inconspicuous when seen either from above or below." The artist Abbott Handerson Thayer formulated what is sometimes called Thayer's Law, the principle of countershading . However, he overstated
9792-474: Is thought to have originated through transposition from symbiotic Aliivibrio fischeri bacteria, which provide bioluminescence to its hosts. While not all cephalopods use active camouflage , ancient cephalopods may have inherited the gene horizontally from symbiotic A. fischeri , with divergence occurred through subsequent gene duplication (such as in the case of Sepia officinalis ) or gene loss (as with cephalopods with no active camouflage capabilities). This
9945-640: Is unique as an instance of camouflage arising as an instance of horizontal gene transfer from an endosymbiont . However, other methods of horizontal gene transfer are common in the evolution of camouflage strategies in other lineages. Peppered moths and walking stick insects both have camouflage-related genes that stem from transposition events. The Agouti genes are orthologous genes involved in camouflage across many lineages. They produce yellow and red coloration ( phaeomelanin ), and work in competition with other genes that produce black (melanin) and brown (eumelanin) colours. In eastern deer mice , over
10098-463: Is usually provided by a battery -powered LED , though other electric light sources can be used. The light is projected forward through the sight, and reflects off the back surface of the reticle. Red is the most common colour used, as it least impedes the shooter's natural night vision . This illumination method can be used to provide both daytime and low-light conditions reticle illumination. Radioactive isotopes such as tritium can also be used as
10251-594: The Cartesian coordinate system , which the shooter can use as a simple reference for rough horizontal and vertical calibrations. Crosshair reticles typically do not have any graduated markings, and thus are unsuitable for stadiametric rangefinding . However some crosshair designs have thickened outer sections that help with aiming in poor contrast situations when the fine crosshair center cannot be seen clearly. These "thin-thick" crosshair reticles, known as duplex reticles , can also be used for some rough estimations if
10404-695: The IMI Tavor TAR-21 (STAR-21), M16A2E3 and M4 carbine. The U.S. Marines use M14s that have been rebuilt at Marine Corps Base Quantico and designated as Designated Marksman Rifles , which are being replaced by the M39 Enhanced Marksman Rifle . The Corps also utilizes two different adaptations of the M16 assault rifle: the Squad Advanced Marksman Rifle (SAM-R), and the Mk 12 Mod 1 SPR . They also utilize
10557-636: The M27 Infantry Automatic Rifle . The United States Army 101st Airborne Division recognized the need for a Squad Designated Marksman when they encountered fires beyond the 300-600m range. In 2004, they began issuing M14s to specially trained soldiers for Designated Marksman work. The 82nd Airborne Division deployed with designated marksmen, trained on the M-4 using ACOGs with great success out to 600m, some 82nd Airborne units were issued M14s. The 3rd Infantry Division saw limited use of
10710-609: The Mk 14 EBR amongst its four-man infantry sections. Recently, the L86A2 Light Support Weapon was used in the designated marksman role due to its longer barrel compared to the standard L85A2 service rifle, which gives an increased range of up to 1000 m (1094 yd) while also capable of giving accurate automatic fire; the automatic fire role is now usually delivered by the Minimi . The Parachute Regiment , Royal Marines and United Kingdom Special Forces also use
10863-502: The Mk 14 Mod 0 Enhanced Battle Rifle or M4 Rifle with fitted optical scopes. Previously, Designated Marksman assigned to NECC's Helicopter, Visit, Search, and Seizure teams were equipped with the M21 (SWS) w/ Leupold Mk4 LR/T after training with the USMC, US Army, and training organizations to deploy the rifle from various platforms (helicopter, ship, ground). Although referred to as "snipers",
11016-495: The StG 44 assault rifle, intended primarily for night use. The issuing of the ZG 1229 Vampir system to the military started in 1944 and it was used on a small scale in combat from February 1945 until the final stages of World War II. Telescopic sights are classified in terms of the optical magnification (i.e. "power") and the objective lens diameter . For example, "10×50" would denote
11169-519: The eyepiece , since the image illuminance is often sufficient without needing an enlarged objective bell to enhance light-gathering. Most LPVOs have reticles mounted at the second focal plane, but recently first-focal plane LPVOs have become popular, especially those with high zoom ratios above 6×. LPVOs are also informally referred to as " AR scopes" or " carbine scopes", due to the recently increasing popularity of modern sporting rifles and compact "tactical"-style semi-automatic rifles used among
11322-548: The gerbil or fennec fox , birds such as the desert lark or sandgrouse , or reptiles like the skink or horned viper . Military uniforms, too, generally resemble their backgrounds; for example khaki uniforms are a muddy or dusty colour, originally chosen for service in South Asia. Many moths show industrial melanism , including the peppered moth which has coloration that blends in with tree bark. The coloration of these insects evolved between 1860 and 1940 to match
11475-409: The green tree-snake are examples". Beddard did however briefly mention other methods, including the "alluring coloration" of the flower mantis and the possibility of a different mechanism in the orange tip butterfly . He wrote that "the scattered green spots upon the under surface of the wings might have been intended for a rough sketch of the small flowerets of the plant [an umbellifer ], so close
11628-401: The horned lizards of North America, have evolved elaborate measures to eliminate shadow . Their bodies are flattened, with the sides thinning to an edge; the animals habitually press their bodies to the ground; and their sides are fringed with white scales which effectively hide and disrupt any remaining areas of shadow there may be under the edge of the body. The theory that the body shape of
11781-501: The law enforcement , home defense and practical shooting enthusiasts crowd. Telescopic sights are usually designed for the specific application for which they are intended. Those different designs create certain optical parameters. Those parameters are: Because a typical telescopic sight has several optical elements with special characteristics and several air-to-glass surfaces, telescopic sight manufacturers use different types of optical coatings for technical reasons and to improve
11934-532: The Accuracy International L96A1 in 7.62×51mm with the similar but larger and more powerful Accuracy International L115A3 rifle chambered in .338 Lapua Magnum. DMs are utilized for targets at ranges between approximately 300–600 metres (330–660 yd) using a rifle chambered with standard-issue rifle ammunition, usually either 5.56×45mm or 7.62×51mm. While snipers often take a fixed strategic position and camouflage themselves (e.g. with
12087-600: The British army having adopted "coats of motley hue and stripes of paint" for snipers. Cott takes the example of the larva of the blotched emerald moth, which fixes a screen of fragments of leaves to its specially hooked bristles, to argue that military camouflage uses the same method, pointing out that the "device is ... essentially the same as one widely practised during the Great War for the concealment, not of caterpillars, but of caterpillar-tractors, [gun] battery positions, observation posts and so forth." Movement catches
12240-663: The Continent persons are warned not to keep white pigeons, as being the most liable to destruction. Hence I can see no reason to doubt that natural selection might be most effective in giving the proper colour to each kind of grouse, and in keeping that colour, when once acquired, true and constant. The English zoologist Edward Bagnall Poulton studied animal coloration , especially camouflage. In his 1890 book The Colours of Animals , he classified different types such as "special protective resemblance" (where an animal looks like another object), or "general aggressive resemblance" (where
12393-482: The Dragunov SVD rifle that shares all the characteristics typical of a designated marksman rifle (Semi-automatic fire, telescopic sight , chambered for standard military rifle cartridge ). Telescopic sight A telescopic sight , commonly called a scope informally, is an optical sighting device based on a refracting telescope . It is equipped with some form of a referencing pattern – known as
12546-633: The HK417 rifle in the designated marksman role. On 28 December 2009, the UK Ministry of Defence announced the adoption of the L129A1 Sharpshooter rifle made by Lewis Machine and Tool Company of the US for use as a semi-automatic DM rifle, firing the 7.62×51mm NATO round , providing accurate fire of up to 1000m as an urgent operational requirement (UOR) in Afghanistan. The Indian Army uses
12699-477: The Soviet Union and its allies have since World War II employed specially-equipped and trained "sharpshooting" soldiers at a section (" squad ") and platoon level to increase the range of their section to 1,000 meters (1,100 yd). This is commonly accepted as the first example of what came to be known as a designated marksman as opposed to a true sniper. Since 1963, these soldiers have been equipped with
12852-518: The UK, US, and other Western countries over the last 15 years, sniper rifles chambered for standard military calibers, such as 7.62×51mm, have been replaced with those that employ larger, more specialized rounds, such as .300 Winchester Magnum or .338 Lapua Magnum, which give better accuracy at longer ranges than the standard military rifle calibers. An example of this is the British Army's replacement of
13005-409: The adults of most of these are opaque and pigmented, resembling the seabed or shores where they live. Adult comb jellies and jellyfish obey the rule, often being mainly transparent. Cott suggests this follows the more general rule that animals resemble their background: in a transparent medium like seawater, that means being transparent. The small Amazon River fish Microphilypnus amazonicus and
13158-483: The agouti gene shows that different organisms often rely on orthologous or even identical genes to develop a variety of camouflage strategies. While camouflage can increase an organism's fitness, it has genetic and energetic costs. There is a trade-off between detectability and mobility. Species camouflaged to fit a specific microhabitat are less likely to be detected when in that microhabitat, but must spend energy to reach, and sometimes to remain in, such areas. Outside
13311-437: The aim high and away from the target, are therefore called holdover reticles . Such aiming technique can quickly correct for ballistic deviations without needing to manually readjust the sight's zero, thus enabling the shooter to place rapid, reliably calibrated follow-up shots. When shooting at extended distances , the farther the target, the greater the bullet drops and wind drifts that need to be compensated. Because of this,
13464-412: The amount of "lost" light present inside the telescopic sight which would otherwise make the image appear hazy (low contrast). A telescopic sight with good optical coatings may yield a brighter image than uncoated telescopic sights with a larger objective lens, on account of superior light transmission through the assembly. The first transparent interference-based coating Transparentbelag (T) used by Zeiss
13617-451: The amount of space within which the relay lens group and other optical elements can be mounted, the maximum size of the erector tube, and the maximum angular ranges for elevation and windage adjustments. Telescopic sights intended for long-range and/or low-light usage generally feature larger main tube diameters. Besides optical, spatial and attainable range of elevation and windage adjustments considerations, larger diameter main tubes offer
13770-532: The available magnification range on FFP sights compared to SFP, and FFP sights are much more expensive compared to SFP models of similar quality. Most high-end optics manufacturers leave the choice between a FFP or SFP mounted reticle to the customer or have sight product models with both setups. Variable-power telescopic sights with FFP reticles have no problems with point of impact shifts. Variable-power telescopic sights with SFP reticles can have slight point-of-impact shifts through their magnification range, caused by
13923-438: The body outline, making it harder to precisely identify and locate. However, disruptive patterns result in higher predation. Disruptive patterns that specifically involve visible symmetry (such as in some butterflies) reduce survivability and increase predation. Some researchers argue that because wing-shape and color pattern are genetically linked, it is genetically costly to develop asymmetric wing colorations that would enhance
14076-456: The body. On these, the nymph spreads an inner layer of fine particles and an outer layer of coarser particles. The camouflage may conceal the bug from both predators and prey. Similar principles can be applied for military purposes, for instance when a sniper wears a ghillie suit designed to be further camouflaged by decoration with materials such as tufts of grass from the sniper's immediate environment. Such suits were used as early as 1916,
14229-511: The bolt-action M24 SWS instead of the M14 rifle. A major change was the introduction of a new battle profession – the designated marksman (קלע סער, "kala sa'ar" in Hebrew ) – intended to improve the accuracy and firepower of an infantry platoon and compromise between the role of a sniper and an assault rifleman. These soldiers were generally called "squad snipers" to describe their role. They are armed with SR-25 rifle and sharpshooter variations of
14382-437: The bottom two quadrants , consisting of elaborate arrays of neatly spaced fine dots, "+" marks or hashed lines (usually at 0.2 mil or ½ MOA intervals), to provide accurate references for compensating bullet drops and wind drifts by simply aiming above (i.e. "hold [the aim] over" the target) and upwind of the target (i.e. deflection shooting , or " Kentucky windage "). This type of reticles, designed to hold
14535-442: The branches of host-coral, Platygyra carnosa , which limits the geographical range and efficacy in nudibranch nutritional crypsis. Furthermore, the nudibranch colour change is not immediate, and switching between coral hosts when in search for new food or shelter can be costly. The costs associated with distractive or disruptive crypsis are more complex than the costs associated with background matching. Disruptive patterns distort
14688-457: The camouflage consists of two surfaces, each with the simple function of providing concealment against a specific background, such as a bright water surface or the sky. The body of a shark or the fuselage of an aircraft is not gradated from light to dark to appear flat when seen from the side. The camouflage methods used are the matching of background colour and pattern, and disruption of outlines. Counter-illumination means producing light to match
14841-468: The case in the 1909 book Concealing-Coloration in the Animal Kingdom , arguing that "All patterns and colors whatsoever of all animals that ever preyed or are preyed on are under certain normal circumstances obliterative" (that is, cryptic camouflage), and that "Not one ' mimicry ' mark, not one ' warning color '... nor any ' sexually selected ' color, exists anywhere in the world where there
14994-403: The change is controlled relatively slowly, mainly by hormones . In fish, the change is controlled by the brain, which sends signals directly to the chromatophores, as well as producing hormones. The skins of cephalopods such as the octopus contain complex units, each consisting of a chromatophore with surrounding muscle and nerve cells. The cephalopod chromatophore has all its pigment grains in
15147-411: The changing colour of the tree trunks on which they rest, from pale and mottled to almost black in polluted areas. This is taken by zoologists as evidence that camouflage is influenced by natural selection , as well as demonstrating that it changes where necessary to resemble the local background. Disruptive patterns use strongly contrasting, non-repeating markings such as spots or stripes to break up
15300-475: The coating, the character of the image seen in the telescopic sight under normal daylight can either "warmer" or "colder" and appear either with higher or lower contrast. Subject to the application, the coating is also optimized for maximum color fidelity through the visible spectrum . A common application technique is physical vapor deposition of one or more superimposed very thin anti-reflective coating layer(s) which includes evaporative deposition , making it
15453-540: The colour-changing abilities, both for camouflage and for signalling , of cephalopods including the octopus, in his Historia animalium : The octopus ... seeks its prey by so changing its colour as to render it like the colour of the stones adjacent to it; it does so also when alarmed . Camouflage has been a topic of interest and research in zoology for well over a century. According to Charles Darwin 's 1859 theory of natural selection , features such as camouflage evolved by providing individual animals with
15606-411: The combination of behaviours and other methods of crypsis involved, young giraffes seek cover, lie down, and keep still, often for hours until their mothers return; their skin pattern blends with the pattern of the vegetation, while the chosen cover and lying position together hide the animals' shadows. The flat-tail horned lizard similarly relies on a combination of methods: it is adapted to lie flat in
15759-414: The commercial and military and law enforcement sights. Older telescopic sights often did not offer internal windage and/or elevation adjustments in the telescopic sight. In case the telescopic sight lacked internal adjustment mechanisms adjustable mounts are used (on the scope rings or the mounting rail itself) for sighting-in . Telescopic sights come with a variety of different reticles , ranging from
15912-504: The countershaded animal nearly invisible against a suitable background. Thayer observed that "Animals are painted by Nature, darkest on those parts which tend to be most lighted by the sky's light, and vice versa ". Accordingly, the principle of countershading is sometimes called Thayer's Law . Countershading is widely used by terrestrial animals , such as gazelles and grasshoppers; marine animals, such as sharks and dolphins ; and birds, such as snipe and dunlin . Countershading
16065-530: The designated marksman rifle is simply an accurized version of the standard service rifle, such as the Mk 12 SPR (which is built on an M16 platform), while in other cases the rifle is a larger caliber rifle design, such as the British L129A1 , Soviet SVD , or US rifles based on the M14 , AR-10 , or HK417 . Whether a modified existing service rifle or a specific design, the DM rifle will be chambered for
16218-502: The efficacy of disruptive cryptic patterning. Symmetry does not carry a high survival cost for butterflies and moths that their predators views from above on a homogeneous background, such as the bark of a tree. On the other hand, natural selection drives species with variable backgrounds and habitats to move symmetrical patterns away from the centre of the wing and body, disrupting their predators' symmetry recognition. Camouflage can be achieved by different methods, described below. Most of
16371-419: The eye of prey animals on the lookout for predators, and of predators hunting for prey. Most methods of crypsis therefore also require suitable cryptic behaviour, such as lying down and keeping still to avoid being detected, or in the case of stalking predators such as the tiger , moving with extreme stealth, both slowly and quietly, watching its prey for any sign they are aware of its presence. As an example of
16524-400: The features of their bodies, and to match their backgrounds. For example, a caddisfly larva builds a decorated case and lives almost entirely inside it; a decorator crab covers its back with seaweed, sponges, and stones. The nymph of the predatory masked bug uses its hind legs and a ' tarsal fan' to decorate its body with sand or dust. There are two layers of bristles ( trichomes ) over
16677-738: The fish accordingly has crystal stacks with a range of different spacings. A further complication for fish with bodies that are rounded in cross-section is that the mirrors would be ineffective if laid flat on the skin, as they would fail to reflect horizontally. The overall mirror effect is achieved with many small reflectors, all oriented vertically. Silvering is found in other marine animals as well as fish. The cephalopods , including squid, octopus and cuttlefish, have multilayer mirrors made of protein rather than guanine. Some deep sea fishes have very black skin, reflecting under 0.5% of ambient light. This can prevent detection by predators or prey fish which use bioluminescence for illumination. Oneirodes had
16830-446: The front post on iron sights . However, most reticles have both horizontal and vertical lines to provide better visual references. The crosshair is the most rudimentary reticle, represented as a pair of smooth, perpendicularly intersecting lines in the shape of a " + ", and the crosshair center is used for aiming the weapon. The crosshair lines geometrically resemble the X- and Y-axis of
16983-482: The genetic components and various ecological pressures that drive crypsis. Camouflage is a soft-tissue feature that is rarely preserved in the fossil record, but rare fossilised skin samples from the Cretaceous period show that some marine reptiles were countershaded. The skins, pigmented with dark-coloured eumelanin , reveal that both leatherback turtles and mosasaurs had dark backs and light bellies. There
17136-436: The genetic components of camouflage in specific organisms illuminates the various ways that crypsis can evolve among lineages. Many cephalopods have the ability to actively camouflage themselves, controlling crypsis through neural activity. For example, the genome of the common cuttlefish includes 16 copies of the reflectin gene, which grants the organism remarkable control over coloration and iridescence. The reflectin gene
17289-418: The highest power. Some long-range shooters and military snipers use fixed-power telescopic sights to eliminate this potential for error. Some SFP sights take advantage of this aspect by having the shooter adjust magnification until the target fits a certain way inside the reticle and then extrapolate the range based on the power adjustment. Some Leupold hunting sights with duplex reticles allow range estimation to
17442-399: The horned lizards which live in open desert is adapted to minimise shadow is supported by the one species which lacks fringe scales, the roundtail horned lizard , which lives in rocky areas and resembles a rock. When this species is threatened, it makes itself look as much like a rock as possible by curving its back, emphasizing its three-dimensional shape. Some species of butterflies, such as
17595-604: The human eye luminous efficiency function variance. Maximal light transmission around wavelengths of 555 nm ( green ) is important for obtaining optimal photopic vision using the eye cone cells for observation in well-lit conditions. Maximal light transmission around wavelengths of 498 nm ( cyan ) is important for obtaining optimal scotopic vision using the eye rod cells for observation in low light conditions. These allow high-quality 21st century telescopic sights to practically achieve measured over 90% light transmission values in low light conditions. Depending on
17748-402: The image they produce. Lens coatings can increase light transmission, minimize reflections, repel water and grease and even protect the lens from scratches. Manufacturers often have their own designations for their lens coatings. Anti-reflective coatings reduce light lost at every optical surface through reflection at each surface. Reducing reflection via anti-reflective coatings also reduces
17901-698: The infantry platoon in the shape of increased precision at a greater range than that provided by the standard infantry rifle, by virtue of its sighting system and/or larger caliber. By comparison, the sniper role is much more specialized, with very comprehensive selection, training and equipment. Snipers are ordinarily equipped with specialized, purpose-built bolt-action or semi-automatic sniper rifles or anti-materiel rifles ; while DMs are often equipped with accurized battle rifles or assault rifles fitted with optical sights and heavy barrels. Snipers are mainly employed for targets at ranges from 600 metres (660 yd) up to more than 2,000 metres (2,190 yd). In
18054-409: The infantry platoon, providing a niche capability contributing to the overall firepower of the platoon in the same way as a grenadier with a rifle-mounted grenade launcher, allowing the team to engage more numerous targets and vehicles; or the automatic rifleman who employs the squad/section machine gun to lay down suppressing fire for area denial to the enemy. The DM weapon provides a capability to
18207-434: The late 1630s, English amateur astronomer William Gascoigne was experimenting with a Keplerian telescope and left it with the case open. Later he found that a spider had spun its web inside the case, and when he looked through the telescope he found that the web was in focus with distant objects. Gascoigne realised that he could use this principle to make a telescopic sight for use in his astronomical observations. "This
18360-423: The local environment. As there is a lack of evidence for camouflage in the fossil record, studying the evolution of camouflage strategies is very difficult. Furthermore, camouflage traits must be both adaptable (provide a fitness gain in a given environment) and heritable (in other words, the trait must undergo positive selection ). Thus, studying the evolution of camouflage strategies requires an understanding of
18513-432: The low magnification range (1–4×, 1–6×, 1–8×, or even 1–10×) are known as low-power variable optics or LPVOs . These telescopic sights are often equipped with built-in reticle illumination and can be dialed down to 1× magnification. As low magnifications are mostly used in close- and medium ranges, LPVOs typically have no parallax compensation (though a few rare models do) and have a completely cylindrical shape ahead of
18666-614: The low magnification ranges (usually 2×, 2.5×, 3× or more commonly 4×, occasionally 1× or 5× or more), suitable for shooting at short/medium distances. One of the best known examples is the battle-proven Trijicon ACOG used by the USMC , US Army, and USSOCOM , although variable-magnification prism sights do also exist, such as the ELCAN Specter DR/TR series used by the Canadian Army . Variable-zoom telescopic sights in
18819-534: The method mainly for its efficiency rather than camouflage. Animals such as chameleon , frog, flatfish such as the peacock flounder , squid, octopus and even the isopod idotea balthica actively change their skin patterns and colours using special chromatophore cells to resemble their current background, or, as in most chameleons, for signalling . However, Smith's dwarf chameleon does use active colour change for camouflage. Each chromatophore contains pigment of only one colour. In fish and frogs, colour change
18972-428: The methods help to hide against a background; but mimesis and motion dazzle protect without hiding. Methods may be applied on their own or in combination. Many mechanisms are visual, but some research has explored the use of techniques against olfactory (scent) and acoustic (sound) detection. Methods may also apply to military equipment. Some animals' colours and patterns match a particular natural background. This
19125-466: The microhabitat, the organism has a higher chance of detection. Generalized camouflage allows species to avoid predation over a wide range of habitat backgrounds, but is less effective. The development of generalized or specialized camouflage strategies is highly dependent on the biotic and abiotic composition of the surrounding environment. There are many examples of the tradeoffs between specific and general cryptic patterning. Phestilla melanocrachia ,
19278-538: The night sky, requiring awkward external platforms to support the lamps. The Canadian concept was refined in the American Yehudi lights project, and trialled in aircraft including B-24 Liberators and naval Avengers . The planes were fitted with forward-pointing lamps automatically adjusted to match the brightness of the night sky. This enabled them to approach much closer to a target – within 3,000 yards (2,700 m) – before being seen. Counterillumination
19431-547: The oldest type of reticles and are made out of metal wire or thread, mounted in an optically appropriate position in the telescopic sight's tube. Etched reticles are an optic element, often a glass plate, with inked patterns etched onto it, and are mounted as an integrated part of the lightpath . When backlit through the ocular, a wire reticle will reflect incoming light and cannot present a fully opaque (black) reticle with high contrast. An etched reticle will stay fully opaque (black) if backlit. Reticle patterns can be as simple as
19584-514: The open desert, relying on stillness, its cryptic coloration, and concealment of its shadow to avoid being noticed by predators. In the ocean, the leafy sea dragon sways mimetically, like the seaweeds amongst which it rests, as if rippled by wind or water currents. Swaying is seen also in some insects, like Macleay's spectre stick insect, Extatosoma tiaratum . The behaviour may be motion crypsis, preventing detection, or motion masquerade, promoting misclassification (as something other than prey), or
19737-468: The optical needs of European hunters who live in jurisdictions that allow hunting at dusk, night and dawn differ from hunters who traditionally or by legislation do not hunt in low light conditions. The main disadvantage of SFP designs comes with the use of range-finding reticles such as mil-dot. Since the proportion between the reticle and the target is dependent on selected magnification, such reticles only work properly at one magnification level, typically
19890-408: The outlines of an animal or military vehicle, or to conceal telltale features, especially by masking the eyes , as in the common frog . Disruptive patterns may use more than one method to defeat visual systems such as edge detection . Predators like the leopard use disruptive camouflage to help them approach prey, while potential prey use it to avoid detection by predators. Disruptive patterning
20043-912: The positioning of the reticle in the mechanical zoom mechanism in the rear part of the telescopic sight. Normally these impact shifts are insignificant, but accuracy-oriented users, who wish to use their telescopic sight trouble-free at several magnification levels, often opt for FFP reticles. Around the year 2005 Zeiss was the first high-end European telescopic sight manufacturer who brought out variable magnification military grade telescopic sight models with rear SFP mounted reticles. They get around impermissible impact shifts by laboriously hand-adjusting every military grade telescopic sight. The American high-end telescopic sight manufacturer U.S. Optics Inc. also offers variable magnification military grade telescopic sight models with SFP mounted reticles. Either type of reticle can be illuminated for use in low-light or daytime conditions. With any illuminated low-light reticle, it
20196-709: The possibility to increase the tube walls thickness (hence a more robust sight) without sacrificing a lot of internal diameter. A telescopic sight can have several manual adjustment controls in the form of control knobs or coaxial rings. All telescopic sights have the first three (diopter, elevation, windage) adjustment controls, and the fourth (magnification) control is offered on variable-power sights. The remaining two adjustments are optional and typically only found on higher-end models with additional features. The windage and elevation adjustment knobs (colloquially called "tracking turrets") often have internal ball detents to help accurately index their rotation, which provide
20349-659: The reach of the fireteam . The growth of the DM rifle can be attributed to two main influences; the near-universal adoption of intermediate cartridges , such as 5.56×45mm , 5.45×39mm , and 7.62×39mm for standard service rifles, which limit the typical effective range of a standard infantryman to within 200–300 metres (220–330 yd); and the increasing specialization over the last 15 years (mid-2000s to late 2010s) of Western sniper rifles and their employment of more powerful rounds, such as .300 Winchester Magnum and .338 Lapua Magnum , which are more suitable for targets beyond 600 metres (660 yd). These two influences have left
20502-528: The reference arrays of holdover reticles are typically much wider at the lower portion, shaping into an isosceles triangle / trapezium that resembles the canopy of a spruce , the ornamental tree traditionally used to make Christmas trees . Holdover reticles therefore are colloquially also known as " Christmas tree reticles ". Well-known examples of these reticles include GAP G2DMR, Horus TReMoR series and H58/H59, Vortex EBR-2B and Kahles AMR. Telescopic sights based on image erector lenses (used to present to
20655-664: The same manner as the Marine Corps and Army, although there is no specific "Designated Marksman" role in a SEAL platoon. Known used weapons include, but are not limited to, the Mk 14 Mod 0 Enhanced Battle Rifle , M110 Semi-Automatic Sniper System , MK11/ SR-25 , the MK12 Mod X, the " SEAL Recon Rifle " and in some cases even regular M14 Rifles fitted with optical scopes. The United States Navy Naval Expeditionary Combat Command employ Expeditionary Designated Marksman to support COCOM / DOD tasking as required. Known used weapons are
20808-474: The same time in Australia , zoologist William John Dakin advised soldiers to copy animals' methods, using their instincts for wartime camouflage. The term countershading has a second meaning unrelated to "Thayer's Law". It is that the upper and undersides of animals such as sharks, and of some military aircraft, are different colours to match the different backgrounds when seen from above or from below. Here
20961-467: The shrimps it associates with, Pseudopalaemon gouldingi , are so transparent as to be "almost invisible"; further, these species appear to select whether to be transparent or more conventionally mottled (disruptively patterned) according to the local background in the environment. Where transparency cannot be achieved, it can be imitated effectively by silvering to make an animal's body highly reflective. At medium depths at sea, light comes from above, so
21114-477: The sides of a tank. The Peltier plate panels are heated and cooled to match either the vehicle's surroundings (crypsis), or an object such as a car (mimesis), when viewed in infrared. Countershading uses graded colour to counteract the effect of self-shadowing, creating an illusion of flatness. Self-shadowing makes an animal appear darker below than on top, grading from light to dark; countershading 'paints in' tones which are darkest on top, lightest below, making
21267-409: The simple crosshairs to complex reticles designed to allow the shooter to range a target, to compensate for the bullet drop, and to adjust 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 sight. For example, with
21420-462: The speckled wood, Pararge aegeria , minimise their shadows when perched by closing the wings over their backs, aligning their bodies with the sun, and tilting to one side towards the sun, so that the shadow becomes a thin inconspicuous line rather than a broad patch. Similarly, some ground-nesting birds, including the European nightjar , select a resting position facing the sun. Eliminating shadow
21573-657: The standard sharpshooter equipment during the American Civil War . Other telescopic sights of the same period were the Davidson and the Parker Hale . An early practical refracting telescope based telescopic sight was built in 1880 by August Fiedler (of Stronsdorf , Austria ), forestry commissioner of German Prince Reuss . Later telescopic sights with extra long eye relief became available for use on handguns and scout rifles . A historic example of
21726-722: The summer to white in the winter; the Arctic fox is the only species in the dog family to do so. However, Arctic hares which live in the far north of Canada , where summer is very short, remain white year-round. The principle of varying coloration either rapidly or with the changing seasons has military applications. Active camouflage could in theory make use of both dynamic colour change and counterillumination. Simple methods such as changing uniforms and repainting vehicles for winter have been in use since World War II. In 2011, BAE Systems announced their Adaptiv infrared camouflage technology. It uses about 1,000 hexagonal panels to cover
21879-769: The target's speed, range, and heading. During and after the Second World War , a variety of camouflage schemes were used for aircraft and for ground vehicles in different theatres of war. The use of radar since the mid-20th century has largely made camouflage for fixed-wing military aircraft obsolete. Non-military use of camouflage includes making cell telephone towers less obtrusive and helping hunters to approach wary game animals. Patterns derived from military camouflage are frequently used in fashion clothing, exploiting their strong designs and sometimes their symbolism. Camouflage themes recur in modern art, and both figuratively and literally in science fiction and works of literature. In ancient Greece, Aristotle (384–322 BC) commented on
22032-470: The theory to a fantastic extreme in an endeavour to make it cover almost every type of coloration in the animal kingdom." Cott built on Thayer's discoveries, developing a comprehensive view of camouflage based on "maximum disruptive contrast", countershading and hundreds of examples. The book explained how disruptive camouflage worked, using streaks of boldly contrasting colour, paradoxically making objects less visible by breaking up their outlines. While Cott
22185-462: The transition point between thinner and thicker lines are at a defined distance from the center, as seen in designs such as the common 30/30 reticles (both the fine horizontal and vertical crosshair lines are 30 MOAs in length at 4× magnification before transition to thicker lines). There can be additional features such as enlarged center dot (frequently also illuminated ), concentric circle (solid or broken/dashed), chevron , stadia bars, or
22338-812: The ubiquitous metric units , as each milliradian at each meter of distance simply corresponds to a subtension of 1 millimeter; while MOA-based reticles are more popular in civilian usage favoring imperial units (e.g. in the United States), because by coincidence 1 MOA at 100 yards (the most common sight-in distance) can be confidently rounded to 1 inch. To allow methodological uniformity, accurate mental calculation and efficient communication between spotters and shooters in sniper teams , mil-based sights are typically matched by elevation/windage adjustments in 0.1 mil increments. There are however military and shooting sport sights that use coarser or finer reticle increments. By means of
22491-551: The user with an upright image) have two planes of focus where a reticle can be placed: at the focal plane between the objective and the image erector lens system (the First Focal Plane (FFP)), or the focal plane between the image erector lens system and the eyepiece (the Second Focal Plane (SFP)). On fixed power telescopic sights there is no significant difference, but on variable power telescopic sights
22644-508: The wavelength of visible light. A familiar example is the transparency of the lens of the vertebrate eye , which is made of the protein crystallin , and the vertebrate cornea which is made of the protein collagen . Other structures cannot be made transparent, notably the retinas or equivalent light-absorbing structures of eyes – they must absorb light to be able to function. The camera -type eye of vertebrates and cephalopods must be completely opaque. Finally, some structures are visible for
22797-447: 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 sight, once both the slope of the terrain and the slant range to target are known. There are two main types of reticle constructions: wire reticle and etched reticle . Wire reticles are
22950-682: Was identified as a principle of military camouflage during the Second World War . Many prey animals have conspicuous high-contrast markings which paradoxically attract the predator's gaze. These distractive markings may serve as camouflage by distracting the predator's attention from recognising the prey as a whole, for example by keeping the predator from identifying the prey's outline. Experimentally, search times for blue tits increased when artificial prey had distractive markings. Some animals actively seek to hide by decorating themselves with materials such as twigs, sand, or pieces of shell from their environment, to break up their outlines, to conceal
23103-478: Was invented in 1935 by Olexander Smakula . A classic lens-coating material is magnesium fluoride , which reduces reflected light from 5% to 1%. Modern lens coatings consist of complex multi-layers and reflect only 0.25% or less to yield an image with maximum brightness and natural colors. Determined by the optical properties of the lenses used and intended primary use of the telescopic sight, different coatings are preferred, to optimize light transmission dictated by
23256-464: Was made obsolete by radar , and neither diffused lighting camouflage nor Yehudi lights entered active service. Many marine animals that float near the surface are highly transparent , giving them almost perfect camouflage. However, transparency is difficult for bodies made of materials that have different refractive indices from seawater. Some marine animals such as jellyfish have gelatinous bodies, composed mainly of water; their thick mesogloea
23409-498: Was more systematic and balanced in his view than Thayer, and did include some experimental evidence on the effectiveness of camouflage, his 500-page textbook was, like Thayer's, mainly a natural history narrative which illustrated theories with examples. Experimental evidence that camouflage helps prey avoid being detected by predators was first provided in 2016, when ground-nesting birds ( plovers and coursers ) were shown to survive according to how well their egg contrast matched
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