Diode Dichroic Filter
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 Laser diode dichroic filter Yag ion argon 1 2X1 Green  US $19.99
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 Laser diode dichroic color filter Yag 1 2 X 1 Cyan US $19.99
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 Laser diode dichroic filter Yag DPSS argon 1 2X1 Red US $19.99
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 Laser diode dichroic filter Yag argon 1 2X1 Magenta US $19.99
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 Laser diode dichroic filter Yag ion argon 1 2X1 Blue US $19.99
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 Laser diode dichroic filter Yag argon 1 2 X 1 Yellow US $19.99
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How Reflex Sights Work
Red dot sights use the optical collimator. Collimators align rays of light from a source in parallel. Refractive and reflective collimators are employed. An image of the reticle, generated by the collimator and illuminated by a fiber-optic or radioactive light source or LED, is projected to infinity. The image is projected onto a dichroic mirror or beam splitter coated so as to reflect only light of the colour of the reticle and to allow all other light pass through. This allows the shooter to see the reticle at a distance in an otherwise perfect image from which only the exact wavelength of the reticle has been subtracted.
Holographic reflex sights substitute a holographic image of the aiming mark or reticle created by a laser diode. Holographic reflex sights use a laser to generate a holographic reticle or aiming mark which the collimator then projects to infinity. A great benefit of this is that the entire aiming pattern image is effectively optically centred - not just its middle. This avoids parallax problems caused by differing eye position relative to the sight. It also means partial obscuration of the aiming window will not prevent the firer seeing the aiming pattern in its entirety. The main drawback of the holographic sight is its laser diode's greater power consumption than an LED - battery lives being measured in hundreds rather than tens of thousands of hours.
The configuration the sight is largely dependent on the position of the collimator. Placing the collimator below the sight window ensures a lightweight sight with the small sighting window as the only protrusion. This can result in a sight line well above the line of the bore which works well with Stoner designed rifles but not as well with most others. It can also result in a less robust sight as the protruding window can be vulnerable. Side mounted collimators enable a tube to be used to contain the workings of the sight. Tubes make for immensely rugged sights and are inherently ambidextrous as you can simply turn the sight 90 degrees in its mount to switch the adjusters from azimuth to elevation.
Reflex sights tend to be 1X magnification as this is best for close quarters, both eyes open shooting. The reticle or red dot size is dictated by the application - a large dot will be easy to acquire and place on target, but it will also obscure much of the target and thus be hard to center accurately, especially at longer ranges. Magnifying reflex sights have become ubiquitous in the War on Terror where target identification is at a premium A bright illuminated aiming mark is used for close ranged shooting, with a traditional reticle for longer ranged engagements. The best example of this philosophy is the Trijicon ACOG which has become standard issue across the United States' armed forces. 1X magnification sights can be turned into low powered scopes by the simple addition of a detachable or flip to side magnifier. Another solution is to put a non magnifying red dot sight on top of the magnifying one - an approach adopted with success by Trijicon with their latest ACOGs.
It is almost universal for reflex sights to use internal adjustment. The sight is mounted rigidly to the weapon and the optics move internally to move the point of impact. The adjustments are calibrated and almost always take the form of audible or tactile clicks. The calibrations vary from manufacturer to manufacturer and model to model. The Aimpoint CompM4s (the most recent incarnation of the US Army M68) for example employs clicks that are 16mm at 100 meters or 1/2" at 80 yards whilst the USMC's AN/PVQ-31B has clicks that move the point of impact 0.33" at 100 yards.
The sights have to cope with different brightnesses of daylight and thus employ variable reticle brightness settings. Some have night vision compatible ranges of settings. Adjustment is accomplished automatically in some models, either electronically or by the amount of light the fiber-optic element can take in from the environment. That can create problems - for example when shooting into brightly lit terrain from a darkened room or bunker. A polarising filter can be employed on some models to reduce the brightness of the image - rotating two polarised lenses can graduate the image from complete brightness to complete black-out. As the sight itself often incorporates a polarising filter, mounting a single adjustable polarising filter can have the same effect. In the past this caused problems with protective eyewear which was also polarised, but the leading manufacturers now use polarities chosen so as not to obscure the target when used with polarised glasses.
It is now standard practice to 'co-witness' iron sights through non magnifying reflex sights. It is unnecessary to align the aiming mark to sit on top of the foresight or anywhere else - it only matters that both systems are zeroed on the target. A popular method is to have the iron sights in the bottom 1:3 of the sight picture and manufacturers like Eotech are starting to make sights with optional risers to enable this; for example their 557.AR223.
Copyright Chris Pieterman 2010
Making a 3d homemade Laser projector
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