Prisms: The binoculars use high-quality BaK-4 glass prisms, which further enhance light transmission, providing brighter and more detailed views ED Objective Lenses: The Celestron SkyMaster Pro ED binoculars utilize Extra-Low Dispersion (ED) glass to virtually eliminate chromatic aberration XLT Coating: All lens surfaces of the binoculars feature Celestron's proprietary XLT optical coating technology, which reduces reflectivity and enhances optical throughput