Celestron SkyMaster Pro ED 20x80 Binocular The BaK-4 roof prisms are

The BaK-4 roof prisms are both phase- and dielectric coated for increased contrast and light transmission along with their fully multi-coated lenses

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Multi-coated lenses improve light transmission

Their ED objectives reduce chromatic aberration resulting in crisper colors and better contrast

Celestron SkyMaster Pro ED 20x80 Binocular The BaK-4 roof prisms areThe Celestron SkyMaster Pro ED 20x80 Binocular is an upgraded version with ED (Extra low Dispersion) 80mm objective lenses which provide images with greatly reduced chromatic aberration for improved contrast, color, and sharpness. The optical path features fully multi coated lenses and BaK 4 prisms all coated with XLT coatings to increase light transmission. The SkyMaster Pro ED's eyepieces are threaded to accept standard 1. 25" astronomical eyepiece