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(US), diopter
a unit for measuring the refractive power of a lens: the reciprocal of the focal length of the lens expressed in metres
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


A measure of the power of a lens or a prism. The diopter (also called dioptrie) is usually abbreviated D. Its dimension is a reciprocal length, and its unit is the reciprocal of 1 m (3.28 ft). See Focal length, Lens (optics)

The dioptric power of a prism is defined as the measure of the deviation of a ray going through a prism measured at the distance of 1 m. A prism that deviates a ray by 1 cm in a distance of 1 m is said to have a power of one prism diopter. See Optical prism

Spectacle lenses in general consist of thin lenses, which are either spherical, to correct the focus of the eye for near and far distances, or cylindrical or toric, to correct the astigmatism of the eye. An added prism corrects a deviation of the visual axis. The diopter thus gives a simple method for prescribing the necessary spectacle for the human eye.

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



the unit of focal power of a lens and other axially symmetrical optical systems. It is indicated by the symbol D; 1 D is equal to the power of a lens or spherical mirror with a main focal length of 1 m. Focal power, expressed in diopters, is the reciprocal of the principal focal length in meters. The power of a converging lens is taken as positive, and that of a diverging lens, negative. The focal power of eyeglasses is given in diopters. Eyeglasses for nearsighted persons have negative focal power (negative number of diopters); those for farsighted persons have positive focal power.



a simple device for fixing the direction to an object—that is, sighting. It consists of two metal plates (the ocular and object diopters) fastened to the ends of an alidade or to a divided circle. The ocular diopter has a small circular hole or narrow slit, and the object diopter has a sight or small fine hair stretched at a certain distance from the ocular diopter. The diopter is used by turning it until, upon looking through the ocular diopter, the object diopter is projected on the object to be sighted. With a sufficient distance between the ocular and object diopters, the accuracy of sighting can be 2-5 minutes of arc. The diopter was described by Heron of Alexandria (c. first century A.D.) and was extensively used earlier in geodetic instruments. At present it is found only in some compasses.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


A measure of the power of a lens or a prism, equal to the reciprocal of its focal length in meters. Abbreviated D.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Ten-year follow-up of photorefractive keratectomy for myopia of more than 6 diopters. Am J Ophthalmol.
I prospectively recruited patients aged 3-6 years with more than 3.0 diopters of hyperopia who presented at Kim's Eye Hospital from January 2011 to March 2013.
Although the wavelength difference between the peak sensitivities of retinal rod and cone cells is only a modest 50 nanometers (roughly one-tenth the wavelength of yellow light), it can produce a half diopter's worth of night myopia when combined with the eye's substantial chromatic aberration, says Donald Miller, also at Indiana University.
The central focusing knob performs two functions: focusing and diopter adjustment.
They have even included a threaded insert for a tripod and an adjustable diopter for the ocular eyepiece.
The Victory Compact 8X20 and 10X25 feature an offset hinge for compact folding, separate knobs for center focusing and diopter adjustment and high-eyepoint eyepieces with lockable push/pull eyecups.
Diopter: a measure of a lens's focusing (or defocusing) power, given in inverse meters.
Other features include nitrogen purging to prevent fogging, click-stop center focus, diopter adjustments, and telescopic eyecups.
@ 1,000 yds.) BSA SilverStar 10-30x50 194@10X Weight Length Company (oz.) (in.) Finish Price BSA 27.5 7.5 B/Silver $85 Porro-prism, center-focus, right-eye diopter adjust, multicoated Magnification & Field of View Company Model Objective (mm) (ft.
An aiming circle on the LCD readout allows users to acquire targets rapidly and a diopter makes correcting for one's own vision a snap.
All binoculars have a diopter adjustment, which accommodates the difference in strength between our left and right eyes.
A diopter correction is a useful feature to consider--rarely do both one's eyes come to the exact same focus, so having the ability to fine-tune the focus of one or both eyepieces will make observing a more pleasurable experience.