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 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 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 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 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 ...