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A dioptre (British spelling) or diopter (American spelling), symbol dpt or D, is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, 1 dpt = 1 m −1. It is normally used to express the optical power of a lens or curved mirror , which is a physical quantity equal to the reciprocal of the focal length ...
A diopter sight is an aperture sight component used to assist the aiming of ranged weapons, mainly firearms, airguns, and crossbows. Diopters function to precisely align the shooter's eye with the front sight and the target, while also producing beneficial optical effects for accurate aiming.
Graphic reconstruction of the dioptra, by Venturi, in 1814. (An incorrect interpretation of Heron's description) A dioptra (sometimes also named dioptre or diopter, from Greek: διόπτρα) is a classical astronomical and surveying instrument, dating from the 3rd century BC.
In modern usage, diopter or dioptre is a measure of the optical power of an optical system. Diopter may also refer to: Historically, a dioptric lens; Any lens system, such as a telescope; A diopter sight; A close-up lens used in photography; A theodolite or similar surveyor's angle measuring device; A dioptra, an old surveying device; An ...
That distance is sometimes given on the filter in millimeters. A +3 close-up lens has a maximal working distance of 0.333 m or 333 mm. The magnification is the focal distance of the objective lens (f) divided by the focal distance of the close-up lens; i.e., the focal distance of the objective lens (in meters) multiplied by the diopter value (D) of the close-up lens:
This page was last edited on 13 December 2024, at 02:50 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may apply.
In old texts, the speculum may also be referred to as a diopter or dioptra. [1] Like an endoscope , a speculum allows a view inside the body; endoscopes, however, tend to have optics while a speculum is intended for direct vision.
Generally, a difference in power of one diopter (1D) is the threshold for diagnosis of the condition. [2] [3] Patients may have up to 3 diopters of anisometropia before the condition becomes clinically significant due to headache, eye strain, double vision or photophobia. [4]