Red dot sight

The red dot sight or reflex sight is an optical firearm sight (also used as an aiming sight for telescopes) that uses a refractive or reflective lens to generate a collimated image of a luminous or reflective reticle. This collimaged image appears to be projected out to a point at infinity, which makes the image of the reticle appear to the user to be projected onto the target. Due to the fact that the reticle image is collimated, magnifying the image of the target is impractical, as it would make the sight too hard to hold steady. The collimated image does have its advantages, however, as the scope can be placed at any distance from the eye without distorting the image of the target or reticle. This makes red dot sights suitable for use on pistols, rifles, or shotguns. The lack of magnification is also an advange in that both eyes can be left open, and the eye that sees the reticle image will automatically superimpose that image with the image from the other eye, giving the shooter normal depth perception and full field of view. This makes the red dot sight very fast and easy to use.

Related Topics:
Firearm - Sight - Telescope - Refractive - Reflective - Lens - Collimated - Infinity - Pistol - Rifle - Shotgun - Depth perception - Field of view

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The most common reticle is a small dot, covering 5 minutes of arc, illuminated by a red LED, hence the common term "red dot sight". Sights that use dot reticles are almost invariably measured in minutes of arc, or "MOA". MOA is a convenient measure for shooters using English units, since 1 MOA subtends approximately 1.0472 inches at a distance of 100 yards (91.44 m). This is generally rounded to 1 inch at 100 yards, which makes MOA a very handy unit to use in ballistics. The 5 MOA dot is small enough not to obscure most targets, and large enough to be easily found in a hurry. For many types of action shooting, a larger dot is preferred; 7, 10, 15 or even 20 MOA dots or rings are used; often these will be combined with horizontal and/or vertical lines to provide a level reference.

Related Topics:
Minutes of arc - LED - English units - Ballistics - Action shooting

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Common light sources used in red dot sights include battery powered lights, fiber optic light collectors, and even tritium capsules. The color of the dot is usually red or amber for visibility against most backgrounds. Some dots are also visible when viewed through night vision devices. Newer red dot sights may use a chevron or triangular light instead of a dot for precision in aiming and range estimation.

Related Topics:
Battery - Fiber optic - Tritium - Night vision - Chevron

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Some of the first red dot sights to appear were "occluded" sights; the image of the target was not visible through the sight. Looking into the sight with just one eye, the shooter saw only a red dot (often passively illuminated with ambient light gathered through fiber optics). With both eyes open, the image of the dot was superimposed by the brain onto the target. Nearly all currently available red dot sights use a curved partially reflective glass as a lens. This lens allows light from the target to pass through unobstructed, but collimates and reflects the light of the reticle back to the shooter's eye, thus allowing for one- or two-eyed aiming.

Related Topics:
Fiber optics - Brain

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The above picture shows the view through an inexpensive Crosman red dot sight mounted on a Crosman air pistol. The reflecting lens in this sight reflects all wavelengths, which is why the image through the sight appears so dark. More expensive sights will reflect only the wavelenths used by the reticle, and will thus have a much brighter image.

Related Topics:
Crosman - Air pistol - Wavelength

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Red dot sights are common in speed shooting sports such as IPSC. Militaries are also beginning to adopt red dot sights, since they are easy and fast to use, and since the dot sights work very well in low light conditions. Most dot sights have either active or passive adjustments for the dot brightness, allowing a very bright dot for high visibility in bright conditions, and a very dim dot to prevent loss of night vision in low light conditions. Since dot sights can be mounted at any distance from the shooter's eye with no issues of focus, military rifle mounts usually place the sight over the forend, about 12 inches (30 cm) from the shooter's eyes. This leaves plenty of room for night vision equipment to be used with the red dot sight.

Related Topics:
IPSC - Night vision

~ ~ ~ ~ ~ ~ ~ ~ ~ ~