from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A unit of measurement of the refractive power of lenses equal to the reciprocal of the focal length measured in meters.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A unit of measure of the power of a lens or mirror, equal to the reciprocal of its focal length in meters. Myopia is diagnosed and measured in diopters.
- n. Any lens system, such as a telescope.
- n. A theodolite or similar surveyor’s angle measuring device.
- n. An alidade.
- n. A surgical speculum.
- n. An instrument for drawing the skull by projections.
from the GNU version of the Collaborative International Dictionary of English
- n. An optical instrument, invented by Hipparchus, for taking altitudes, leveling, etc.
from The Century Dictionary and Cyclopedia
- n. An ancient form of theodolite.
- n. The alidade or index arm of a graduated circle.
- n. An instrument used in craniometry for obtaining projections of the skull.
- n. A dioptric.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a unit of measurement of the refractive power of a lens which is equal to the reciprocal of the focal length measured in meters; used by oculists
A diopter is a unit of measurement that indicates the amount of correction needed to change your vision to be as close to 20/20 as possible.
The diopter is a little adjustment that you can make to how your viewfinder works - it's particularly useful for people with poor eye sight - it's usually a little wheel next to your viewfinder.
Also connected with this is checking the 'diopter' on your camera (if it has one.
Well, after archery today (I shot pretty well for somebody who is probably a quarter of a diopter off in the prescription for her dominant eye, currently) and dinner, I went after the poor shedding GRD with an undercoat rake.
Even the best (read extravagantly expensive) binocular on the market will give you a fuzzy view of the world until you correctly set the diopter ring.
Adjusting the diopter the right way makes all the difference.
Look at the same object, and turn the diopter ring (see inset) to bring the object into sharp focus.
If your visual acuity changes during the year, you may need to reset the diopter.
Set properly, a diopter will not only max out the performance of a high-end binocular but even boost the sharpness of budget glass.
Make a note of the diopter-ring setting, or place a small dot of fingernail polish on the correct adjustment.