Reflex Sights

Thursday, September 29th, 2011

In the 20th century, troops carried rifles with good old-fashioned iron sights, which are simple and rugged, but require a fair amount of practice to use well, because the shooter needs to focus on the front sight while nonetheless aiming at a distant target. A few specialist snipers and sharpshooters carried rifles with telescopic sights, which are complicated and fragile.

Modern 21st-century troops carry carbines with reflector (or reflex) sights, which are often called red-dot sights, because they seem, through an optical trick, to place a red dot on the target. Oddly, this isn’t a new technology:

The idea of a reflector sight originated in 1900 with Irish optical designer and telescope maker Sir Howard Grubb in patent No.12108. Grubb conceived of his “Gun Sight for large and small Ordnance” as a better alternative to the difficult to use iron sight while avoiding the telescopic sight’s limited field of view, greater apparent target speed, parallax errors, and the danger of keeping the eye against an eye stop. In the 1901 Scientific Transactions of the Royal Dublin Society he described his invention:

It would be possible to conceive an arrangement by which a fine beam of light like that from a search light would be projected from a gun in the direction of its axis and so adjusted as to correspond with the line of fire so that wherever the beam of light impinged upon an object the shot would hit. This arrangement would be of course equally impracticable for obvious reasons but it is instanced to show that a beam of light has the necessary qualifications for our purposes.

Now the sight which forms the subject of this Paper attains a similar result not by projecting an actual spot of light or an image on the object but by projecting what is called in optical language a virtual image upon it.

It was noted soon after its invention that the sight could be a good alternative to iron sights and also had uses in surveying and measuring equipment. The reflector sight was first used on German fighter aircraft in 1918 and widely adopted on all kinds of fighter and bomber aircraft in the 1930s. By World War II the reflector sight was being used on many types of weapons besides aircraft, including anti-aircraft guns, naval guns, anti tank weapons, and many other weapon where the user needed the simplicity and quick target acquisition nature of the sight. Through their development in the 30’s and into WWII the sight was also being referred to in some applications by the abbreviation “reflex sight”.

The modern red dot sight goes back to the 1970s, when red LEDs finally provided a bright, yet small and energy-efficient light-source suitable for small arms.

Because the sight spits out an image composed of collimated light, the dot remains on target even if the shooter moves his (dominant) eye out of alignment. There’s negligible parallax error.


  1. Doctor Pat says:

    I’ll note that his original idea as described in his patent as “of course equally impracticable for obvious reasons” became practical with the invention of the laser and is now widely used too.

  2. Slovenian Guest says:

    They also had infra-red night-sighting early on:

    M3 Infrared Sniper Rifle
    M1 Infrared Sniper Rifle

    Night-Fighting Panthers
    The Last Panther in Pomerania

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