What is meant by diopter?
A. Diopter is a term used to identify the refractive or light bending capacity of a lens. In magnifiers, there is a direct correlation between focal length and diopter given by the simple formula f = 39.4/d, where d is the diopter number and f is the focal length. Thus, a lens rated at 5 diopters (d = 5) has a focal length of about 8″ (39.4/5 = 7.9). The diopter of a lens is also simply related to its magnifying power by the simple relation MP = d/4 + 1. Thus, a lens with a 5 diopter rating has a magnification power of 2.25x (5/4 + 1 = 2.5).
