A prism sight or prismatic sight, sometimes also called prism scope or prismatic scope, is a type telescopic sight which uses a reflective prism for its image-erecting system, instead of the series of relay lenses found in traditional telescopic sights. The use of prisms makes it possible to construct a shorter and lighter sight, or with an offset between the eyepiece and objective axes.
Prism sights are a type of telescopic sight with similar features and limitations. Most prism sights use roof prisms commonly seen in compact binoculars and spotting scopes. The reticle is etched onto one of the internal reflective surface of the prism, making it easy to illuminate the reticle from the back of the prism even when active illumination is turned off.
Prism sights often have fixed low-power magnification such as 1× (parity magnification or "non-magnifying"), 2×, 3× or 4x magnifications, sometimes 5× or more. Although the low magnification range means not the most visual details when aiming and observing targets, it allows larger fields of view, making them best suited for shooting at short or medium engagement distances.
There are prism sight designs with variable magnification, such as the ELCAN Specter DR/TR series.
Like telescopic sights, prism sights have an etched reticle which makes them suitable for shooters with astigmatism, unlike reflex sights or holographic sights which may be near useless for these shooters depending on the severity of the astigmatism. The reticle is often illuminated, and is visible without illumination. Etched reticles make for the possibility to have more advanced reticles. Some prism sights are available with ballistic reticles which can be used for holdover for shooting at varying distances without turning the adjustment knobs.
Prism sights usually have eyepieces with adjustable diopters so that the image can be adjusted for nearsightedness or farsightedness.
Prism sights have a somewhat larger parallax error than red dot sights. Usually, they do not have an adjustable parallax like some telescopic sights. [1]
Another disadvantage is eye distance. [2] Like telescopic sights, the eye must be within a certain distance from the scope.
Prisms have been used in binoculars since the 1890s. [3] During World War I, the US Army chose to equip the M1903 Springfield repeating rifle for the sniper rifle role by mounting a sight similar to half a binocular, a prismatic sight developed by the Warner & Swasey Company. [4] It was a short and compact sight, and the prisms allowed the objective to be angled to the side so that the 1903 rifle could be loaded with a clip from above. It was still possible to use the iron sights with the scope mounted. [4]
The M1908 version of the scope had 6-times magnification, while the later M1913 version had slightly less magnification at 5.2×. The background for choosing a lower magnification was a larger field of view and improved light transmission. [4] The sight was constructed of steel and brass, was painted black inside for optical performance, and had a relatively high mass of 1,020 g (36 oz). [4] The eye relief was only 38 mm (1.5 in), so the sight was equipped with a rubber eyepiece shield to prevent the scope from hitting the face during recoil. The reticle was a thin crosshair, as was common for this time period. [4]
These sights were fitted to the Hotchkiss M1909 Benét–Mercié machine gun. [5] Canadian Forces ordered 500 samples of the 5.2× variant. [6] Moisture on the inside of the lenses was one of several problems in the field, [6] and the scope was known to loosen. [7] [8] In total, approximately 8,000 units of these prismatic sights were produced. The scope sight had the greatest magnification of the First World War, but in return only had a 4.5 degree field of view. [6]
A well-known later example is the fixed-magnification Trijicon ACOG which has been used in combat by the US Marine Corps, US Army and USSOCOM. [9]
In the 2010s, several manufacturers including Trijicon, and Vortex began offering prism sights on the consumer market.
In October 2019, the Chinese QBZ-191 automatic rifle was revealed at the 70th Anniversary National Day military parade. It has a 3× daylight prismatic sight called QMK152 and QMK-171A.
Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes when viewing distant objects. Most binoculars are sized to be held using both hands, although sizes vary widely from opera glasses to large pedestal-mounted military models.
A spotting scope is a compact lightweight portable telescope optimized for detailed observation of distant objects. They are used as tripod mounted optical enhancement devices for various outdoor activities such as birdwatching, skygazing and other naturalist activities, for hunting and target shooting to verify a marksman's shot placements, for tactical ranging and surveillance, and for any other application that requires higher magnification than ordinary binoculars.
A monocular is a compact refracting telescope used to magnify images of distant objects, typically using an optical prism to ensure an erect image, instead of using relay lenses like most telescopic sights. The volume and weight of a monocular are typically less than half of a pair of binoculars with similar optical properties, making it more portable and also less expensive. This is because binoculars are essentially a pair of monoculars packed together — one for each eye. As a result, monoculars only produce two-dimensional images, while binoculars can use two parallaxed images to produce binocular vision, which allows stereopsis and depth perception.
The M1903 Springfield, officially the United States Rifle, Caliber .30-06, Model 1903, is an American five-round magazine-fed, bolt-action service repeating rifle, used primarily during the first half of the 20th century.
The Advanced Combat Optical Gunsight (ACOG) is a series of prismatic telescopic sights manufactured by Trijicon. The ACOG was originally designed to be used on the M16 rifle and M4 carbine, but Trijicon has also developed ACOG accessories for other firearms. Models provide fixed-power magnification levels from 1.25× to 6×. ACOG reticles are illuminated at night by an internal tritium phosphor. Some versions have an additional daytime reticle illumination via a passive external fiberoptic light pipe or are LED-illuminated using a dry battery. The first ACOG model, known as the TA01, was released in 1987.
A reticle, or reticule also known as a graticule, is a pattern of fine lines or markings built into the eyepiece of an optical device such as a telescopic sight, spotting scope, theodolite, optical microscope or the screen of an oscilloscope, to provide measurement references during visual inspections. Today, engraved lines or embedded fibers may be replaced by a digital image superimposed on a screen or eyepiece. Both terms may be used to describe any set of patterns used for aiding visual measurements and calibrations, but in modern use reticle is most commonly used for weapon sights, while graticule is more widely used for non-weapon measuring instruments such as oscilloscope display, astronomic telescopes, microscopes and slides, surveying instruments and other similar devices.
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 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 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 eye relief of an optical instrument is the distance from the last surface of an eyepiece within which the user's eye can obtain the full viewing angle. If a viewer's eye is outside this distance, a reduced field of view will be obtained. The calculation of eye relief is complex, though generally, the higher the magnification and the larger the intended field of view, the shorter the eye relief.
A milliradian is an SI derived unit for angular measurement which is defined as a thousandth of a radian (0.001 radian). Milliradians are used in adjustment of firearm sights by adjusting the angle of the sight compared to the barrel. Milliradians are also used for comparing shot groupings, or to compare the difficulty of hitting different sized shooting targets at different distances. When using a scope with both mrad adjustment and a reticle with mrad markings, the shooter can use the reticle as a ruler to count the number of mrads a shot was off-target, which directly translates to the sight adjustment needed to hit the target with a follow-up shot. Optics with mrad markings in the reticle can also be used to make a range estimation of a known size target, or vice versa, to determine a target size if the distance is known, a practice called "milling".
The major components of sniper equipment are the precision sniper rifle, various optical scopes and field glasses, specialized ammunition and camouflage materials for the sniper’s body and equipment. A sniper’s spotter typically also wears camouflage. In the 2010s, a spotter uses various optical gear and in some cases a laser rangefinder. Snipers may also use monopods, bipods or tripods to steady their aim.
The C79 Optical sight is a small arms telescopic sight. Elcan names it as the SpecterOS3.4x, but in Canadian service, it is typically referred to as the C79 or the C79A2. A variant, the M145 Machine Gun Optic is in use by the US military. It is 3.4×28, meaning 3.4x magnification, and a 28mm diameter objective lens. A tritium illuminated reticle provides for normal and low-light conditions sighting. It can be mounted to a variety of rifles and light machine guns using the M1913 Picatinny rail mounting system or the similar "Diemaco" rail system found on small arms produced by Diemaco/Colt Canada. It is manufactured by Elcan and can be found on military service weapons around the world. Similar rifle sights are the Sight Unit Small Arms, Trilux (SUSAT) and the Advanced Combat Optical Gunsight (ACOG).
Schmidt & Bender is a German company specialized in producing high end telescopic sights for hunting, sports, law enforcement and military arms.
The PSO-1 is a 4×24 telescopic sight manufactured in Russia by the Novosibirsk instrument-making factory and issued with the Russian military Dragunov sniper rifle. It was introduced on 3 July 1963 together with the Dragunov sniper rifle.
The ZF41 was an optical sight produced in Germany during the Second World War.
A red dot sight is a common classification for a non-magnifying reflector sight that provides an illuminated red dot to the user as a point of aim. A standard design uses a red light-emitting diode (LED) at the focus of collimating optics, which generates a dot-style illuminated reticle that stays in alignment with the weapon the sight is attached to, regardless of eye position.
The PU scope is a 3.5×21 telescopic sight of Soviet manufacture, widely used since 1940 on the SVT-40 rifle for which it was originally designed and since 1942 on the Mosin–Nagant rifle. Before converting the PU for Mosin–Nagant Model 1891/30 sniper rifles these rifles used 3.87×30 PE(M) telescopic sights, a Soviet-made copy of a German Zeiss design, while later rifles used smaller, simpler, and easier-to-produce 3.5×21 PU telescopic sights. The PU telescopic sight has a fixed at 3.5 power magnification. The reticle could be adjusted vertically for range, and the elevation turret is graduated from 0–1,300 m (0–1,422 yd) in 100 m (109 yd) increments. The bullet drop compensation (BDC) adjustment in the elevation turret is free spinning under grease friction. The windage adjustment turret of the telescopic sight features more conventional click adjustments in milliradian increments. The design turned out to be so successful and in demand that production was not stopped after World War II and the sight was converted for and used on other small arms.
The PSL is a Romanian military designated marksman rifle. It is also called PSL-54C, Romak III, FPK and SSG-97. Though similar in appearance, mission, and specifications to the SVD Dragunov, the PSL rifle is, mechanically speaking, completely different as it is based on the AKM assault rifle - with its internals simply being scaled up to accommodate the more powerful 7.62×54mmR cartridge.
The SUIT sight is a 4× prism sight with tritium-powered illumination, utilised at dusk or dawn. The full name is the L2A2 Sight Unit Infantry Trilux. The sight is not designed as a sniper sight, but as a standard issue infantry sight to improve the infantryman's night fighting capability and to assist target identification at long range in daylight and in poor light conditions.
1P78 is a telescopic sight manufactured by Novosibirsk Instrument-Making Plant and in use with the Russian Armed Forces, intended as a replacement for the older PSO-1 and 1P29 scopes currently being used by the Russian military. The optic is intended to become the standard issue sight for the infantry riflemen within the Russian military.
A sight magnifier is an optical telescope that can be paired with a non-magnifying optical sight on a weapon to create a telescopic sight. They work with the parallel collimated reticle image produced by red dot sights and holographic weapon sights. They may synonymously be referred to as a red dot magnifier, reflex sight magnifier, holographic sight magnifier, or flip to side magnifiers.