| An achromatic Lens sight, commonly called a scope, | | | | basis of the intended use. |
| is an optical device used to give additional accuracy | | | | There are also apochromatic telescope sights with |
| using a point of aim for firearms, airguns and | | | | variable magnification. The magnification can be varied |
| crossbows. Other sighting systems are iron sights, | | | | by manually operating a zoom mechanism. Variable |
| reflex sights, and laser sights.The first experiments | | | | sights offer more flexibility regarding shooting at |
| directed to give shooters optical aiming aids go back | | | | varying ranges, targets and light conditions and offer |
| to the early 17th century. For centuries different | | | | a relative wide field of view at lower magnification |
| optical aiming aids and primitive predecessors of | | | | settings. The syntax for variable sights is the |
| telescopic sights were created that had practical or | | | | following: minimal magnification – maximum |
| performance limitations. The first Apochromatic | | | | magnification × objective lens, for example, |
| refractor telescope based telescopic sight was built in | | | | 3–9×40. |
| 1880 by August Fiedler (Stronsdorf, Austria), forestry | | | | Confusingly, some older telescopic sights, mainly of |
| commissioner of Prince Reuss. Telescopic sights with | | | | German or other European manufacture, have a |
| extra long eye relief are available for handgun and | | | | different classification where the second part of the |
| scout rifle use. A historic example of a telescopic | | | | designation refers to 'light gathering power.' In these |
| sight with a long eye relief is the German ZF41 which | | | | cases, a 4×81 (4× magnification) sight would be |
| was used during World War II on Karabiner 98k rifles. | | | | presumed to have a brighter sight picture than a |
| Telescopic sights are classified in terms of the optical | | | | 2.5×70 (2.5× magnification), but the objective |
| magnification and the objective lens diameter, e.g. | | | | lens diameter would not bear any direct relation to |
| 10×50. This would denote 10 times magnification | | | | picture brightness, as brightness is affected also by |
| with a 50 mm objective lens. In general terms, larger | | | | the magnification factor. Typically objective |
| objective lens diameters, due to their ability to gather | | | | Achromatic lenses on early sights are smaller than |
| larger amounts of light, provide a larger exit pupil and | | | | modern sights, in these examples the 4×81 would |
| hence provide a brighter image at the eyepiece. On | | | | have an objective approximately 32mm diameter and |
| fixed magnification sights the magnification power | | | | the 2.5×70 might be approximately 25mm. |
| and objective diameter should be chosen on the | | | | source:intane. |