dioptre

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dioptre

A measure of lens power. The reciprocal of the focal length in metres. A lens of 1 m focal length has a power of 1 dioptre. A lens of 50 cm focal length has a power of 2 dioptres. One of 33.3 cm focal length has a power of 3 dioptres. Dioptres are used by opticians in preference to focal lengths because they can immediately be added together or subtracted during vision testing.

dioptre

1. A unit proposed by Monoyer to evaluate the refractive power of a lens or of an optical system. It is equal to the product of the refractive index in the image space and the reciprocal of the focal length in metres. (Symbol: D.) Thus a lens with a focal length (in air) of 1 m has a power of 1 D, one with a focal length of 1/2 m, has a power of 2 D, etc. 2. It is also incorrectly used to represent a unit of curvature, being equal to the reciprocal of the radius of curvature expressed in metres. See curvature of a surface; myodioptre; fundamental paraxial equation; refractive error; vergence.
Fig. D3 Effect of an 8 Χ prism

 Table D3 Relationship between dioptres and focal length (in air) focal length dioptre value (cm) (in) 0.25 400 157 0.50 200 79 1.00 100 39 1.50 67 26 2.00 50 20 2.50 40 16 3.00 33.3 13 4.00 25 10 5.00 20 7.9 6.00 16.7 6.6 7.00 14.3 5.6 8.00 12.5 4.9 9.00 11.1 4.4 10.00 10 3.9 12.00 8.3 3.3 14.00 7.1 2.8 16.00 6.2 2.4 20.00 5.0 2.0

 Table D4 Relationship between prism dioptres and degrees prism dioptres (Χ) degrees (º) minutes (′) 1 0.573º 0º34′ 2 1.14º 1º8′ 3 1.71º 1º43′ 4 2.28º 2º17′ 5 2.85º 2º51′ 6 3.43º 3º26′ 7 4.0º 4º0′ 8 4.57º 4º34′ 9 5.14º 5º8′ 10 5.71º 5º43′ 15 8.57º 8º34
References in periodicals archive ?
11% Table 5: Mean deviation in prism diopters before and after injection Visit Deviation in Prism Diopters mean +/- SD Pre treatment 33.
A locking diopter ring, focus lock, phase-corrected coatings, fully multicoated lenses and rubber armoring make these binoculars every bit the equal of many brands costing twice as much.
waterproof, phase-coated, center-focus roof prisms come with a click-stop diopter ring for worry-free field use.
The Eye-Q system, manufactured by WaveLight AG, corrects one diopter of nearsightedness or farsightedness in just two seconds.
50 diopters, and I've found glasses (or a corrector lens) mandatory for all critical observing at low and medium powers - in fact, anytime the telescope's exit pupil is 1 millimeter or larger.
Unless your astigmatism is worse than about 3 diopters only medium and low powers will require correction, and then only if the eyepiece itself lacks the eye relief you need to wear glasses.
I wanted to do LASIK, but it wasn't an option for me because of my poor eyesight and the thinness of my cornea," said Chuck Thompson, a New York City lawyer whose prescription was a debilitating -15 diopters.
The Verisyse lens implant is approved for the treatment of nearsightedness for prescriptions as high as -20 diopters.
Schwiegerling estimates that an amateur astronomer whose dark-adapted pupils span 6 millimeters typically will experience a half diopter of night myopia, while the rare stargazer whose pupil can open up as wide as 8 mm may experience a 1 1/2-diopter effect--though both numbers vary widely within the human population.
Rick Fienberg and I both have added a full diopter of myopia correction to our nominal prescriptions, and we both find that this has driven our respective visual limits down by about a half magnitude while greatly enhancing our views of the Milky Way.

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