Take one look through a binocular or spotting scope equipped with ED glass, and you’ll immediately notice the vivid, lifelike color and razor-sharp images. But what exactly gives ED glass its signature look?
ED stands for "extra-low dispersion," which refers to the composition and optical properties of the glass used for the lenses. ED glass is specially formulated and contains rare-earth compounds that greatly reduce a visual defect called chromatic aberration. Also known as “color fringing,” chromatic aberration occurs when the wavelengths for different colors of light do not converge on the same focal plane. It’s most apparent when viewing light colored objects on a dark colored background and looks like an unnatural “halo” effect that softens the focus of the overall image.
Compared to standard crown and flint glasses, ED virtually eliminates chromatic aberration. The result is sharper images with better contrast since the fringes are no longer present.
In addition to eliminating visual defects, ED’s high quality, rare-earth elements are known for producing images with outstanding, true-to-life color and excellent light transmission. These differences become even more apparent when lighting conditions are dim, like at dawn or dusk.
Although ED glass brings phenomenal benefits, it’s important to note that not all ED glass is created equal. There is no official standard or definition for ED, so some manufacturers may try to cut corners and only use a small amount of the crucial components. The result is technically ED, but devoid of the sharpness and richness that ED typically provides. Celestron’s ED glass always comes from reputable sources and contains ample amounts of the quality components needed. Add to that the expert craftsmanship that goes into every Celestron ED binocular, and the results are crystal clear.