Extra Low Dispersion (ED)
ED, which stand for extra low dispersion, is an adjective that describes a feature of glass that used to make lenses for cameras or telescopes. Extra low dispersion glass prevents chromatic aberration because it concentrates and directs the wavelength of light more effectively onto the camera’s film.
Lenses made from extra low dispersion glass have less air bubbles and glass deformities that are more likely to cause image distortion.
Consequently, most professionals and some serious amateurs are more likely to buy higher end cameras that come equipped with extra low dispersion glass lenses. Pictures taken with ED lenses tend to be clearer and sharper with little or no chromatic aberration.
Similarly, astronomers, researchers and other scientists usually use telescopes and microscopes that have extra low dispersion lenses. By looking through ED lenses, researchers can get an accurate visual representation (and, therefore, an accurate measurement) of their subjects.