May 6 2014
A diopter is the unit of measurement of the optical power of a lens or a curved mirror. In terms of numerical value, it is equal to the reciprocal of the focal length of a lens of a curved mirror measured in meters. In other words, a diopter is the unit of reciprocal length.
The power of a lens to change the convergence of light is called its optical power. This power is expressed in the form of diopter rating.
The optical power is the most suitable parameter (rather than the focal length) for use in the lens-maker's equation, since all the other parameters in the equation are reciprocals. Another advantageous feature of expressing the optical power as diopters is that when thin lenses are placed close together their powers sum up.
Applications of Diopter
A diopter, being a measurement of the optical power of a lens, is used in making many useful calculations for vision correction, measuring curvature of lenses, etc.
- Vision Correction – The power of a lens is significant in the field of ophthalmology. It helps an eyecare professional prescribe corrective lenses for correcting the eye’s power. Knowledge of the required power for correcting eye defects helps the eyecare professional to locate the lens with the appropriate diopters of power. Convex lenses have a positive dioptric, hence they are used for hyperopia correction. On the other hand, concave lenses, having a negative dioptric, are used for myopic correction
- Curvature of Lens – A diopter may also be used for measuring the curvature of lenses. The curvature of the lens measured using diopters is the reciprocal of the radius measured in meters. Using diopters for measuring the curvature is reasonably accurate, as long as the thickness of the lens is much less than its radius of curvature
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