The Celestron SkyMaster Pro ED 15x70 Binoculars features 70mm objective lens, nitrogen purged BaK-4 prisms and fully XLT multi-coated optics for brighter more detailed images. Superior optics, coatings, internal components, and housing materials are used in the SkyMaster Pro ED. The SkyMaster Pro ED raises the bar for astronomical binoculars with its big objective lenses, BaK-4 prisms, ED glass, and completely multi-coated optics using Celestron's exclusive XLT coating technology.nED Wide Angle Lensesn Chromatic aberration, often known as colour fringing, is a visual phenomenon frequent in amplified optical systems. Extra-Low Dispersion ED glass essentially eliminates this effect. SkyMaster Pro ED offers razor-sharp photos with super.