page_title: Diopter sight
section_title: Diopter rear sight
hierarchical_section_title: Diopter sight / Diopter rear sight
caption_attribution_description: English: Rear, rotating diopter drum sight of a SIG SG 550 assault rifle. The viewing aperture (hole) above the "3" (denoting the 300 m setting) can be seen.
context_page_description: The diopter is an aperture sight component used to assist the aiming of devices, mainly firearms, airguns, and crossbows. It is found in particular as a rear sight element on rifles.
  To obtain a usable sighting line the diopter has to have a complementing front sight element.
  Diopter and globe sighting lines are commonly used in ISSF match rifle shooting events.
context_section_description: The diopter is in principle a height and sideways (elevation and windage) adjustable occluder with a small hole (aperture), and is placed close in front of the shooter's aiming eye. Through this small hole the shooter can view the front sight component(s) and the intended target.
  The typical occluder used in target shooting diopters is a disc of about 25 mm (0.98 in) in diameter with a small hole in the middle.
  The small diopter viewing opening ensures the shooter's eye is very precisely and consistently centered behind the diopter sight. The diopter sight is easy to use and usually allows for very accurate aiming, because a relative long sighting line can be used. A long sighting line helps to reduce eventual angle errors and will, in case the sight has an incremental adjustment mechanism, adjust in smaller increments when compared to a further identical shorter sighting line.
caption: Rear, rotating diopter drum sight of a SIG SG 550 service rifle. The viewing aperture above the "3" (denoting the 300 m setting) can be seen.
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