A unit used to express the power of magnifying glasses.
The power of a lens in diopters is the reciprocal of its focal length in meters; e.g. a 2-diopter lens has a focal length of 0.5m.
Screw-in magnifying lenses, which can be fitted to the front of a camera lens, are sometimes referred to loosely as 'diopters'.
Diopter Adjustment - This has nothing to do with lenses but adjusts the optical viewfinder's magnification factor to suit the eyesight of the user. Look for a knob or dial next to or beneath the viewfinder's eyepiece. Not all cameras have this feature.