Telescopic sight
From Freepedia
A telescopic sight, commonly referred to as a scope, is a device used to give an accurate point of aim for a firearm. Other sighting systems are iron sights, red dot sights, and laser sights.
Telescopic sights are classified in terms of the optical magnification and the objective lens diameter, e.g. 10 x 50. This would denote 10 times magnification with a 50 mm objective lens. In general terms, larger objective lens diameters are better (collect more light and give a wider field of view), the magnification power should be chosen on the basis of the intended use. There are also Adjustable Objectives sights where the magnification can be changed by manually turning one part, the syntax is the following : minimal magnification - maximum magnification x objective lens, e. g. 3-9x40.
Telescopic sights have both advantages and disadvantages relative to iron sights. Standard doctrine with iron sights is to focus the eye on the front sight and align it with the resulting blur of the target and the rear sight; most shooters have difficulty doing this, as the eye tends to be drawn to the target, blurring both sights. Telescopic sights allow the user to focus on both the crosshair and the target at the same time, as the lenses project the crosshair into the distance (50 to 100 yards or meters for rimfire scopes, 150 or more for centerfire calibers). This, combined with telescopic magnification, clarifies the target and makes the target stand out against the background. The main disadvantage is due to the magnification; when the target is magnified, the area to either side of the target is obscured by the tube of the sight. The higher the magnification, the narrower the field of view in the sight, and the more area that is hidden. Rapid fire target shooters used red dot sights, which have no magnification; this gives them the best field of view while maintaining the single focal plane of a telescopic sight. Telescopic sights are expensive, and require additional, different training to align. Sight alignment with telescopic sights is a matter of making the field of vision circular to minimize parallax error.
Military use of telescopic sights has generally been restricted to snipers on account of their fragility. The glass lenses are prone to breakage, environmental contitions such as condensation, precipitation, dirt, and mud can obscure the external lenses, and the scope tube adds significant bulk to the rifle. Some militaries do issue telescopic sights to their infantry, but they are usually low magnification sights like red dot sights. Snipers generally used moderate to high magnification scopes with special reticals that allow them to estimate range to the target. Telescopic sights also provide some tactical disadvantages. Snipers rely on stealth and concealment to get close to their target, and a telescopic sight can hinder this. Sunlight may reflect from lenses, and a sniper raising his head higher to use telescopic sights might reveal his position. The famous Finnish sniper Simo Häyhä preferred to use iron sights rather than telescopic sights to present less of a target.
Links:
- http://www.airguns-online.co.uk/telescopic_sights.htm UK Scope equipment
