ABO NOCE Practice Test 2026 - Free Optician Certification Practice Questions and Study Guide

The formula used to calculate Diopter (D) is D = 1/F, where F represents the focal length of a lens in meters. Diopters are a measure of lens power and indicate how strongly a lens converges or diverges light. A positive Diopter value indicates a converging lens (convex), while a negative value indicates a diverging lens (concave).

When the focal length is expressed in meters, this formula illustrates that the power of a lens increases as the focal length decreases. For instance, if a lens has a focal length of 1 meter, it has a power of 1 Diopter. If the focal length is halved to 0.5 meters, the power becomes 2 Diopters. This relationship is crucial in optometry for determining the appropriate lens strength needed for vision correction.

The other formulas do not accurately represent the relationship between Diopter and focal length. For example, the equations involving multiplication or division of focal length by constants do not reflect the inverse relationship defined in the actual formula.