What are the different types of Prism coatings?

• Dielectric Coating – a high-reflectivity prism coating that provides high reflectivity across the entire range of visible light and acts as a dielectric mirror - thus providing both sharper colors and crisper images. 
• High Reflectivity Metallic Coating – metallic material such as aluminum or silver is applied to the reverse side of a prism surface that is not totally reflective to raise the reflectivity of the prism mirror surface. Silver coated prisms are more reflective than aluminum coated prisms and can have reflectivity in the high 90% range.
• Phase Coating – optical coatings that are applied to one surface of the shorter light path half of the prism. The coating slightly slows down the short light path half of the incoming light that passes through that surface, causing it to once again be in phase with the light that traveled the longer path when they halves are rejoined.  With phase-corrected prisms, no colors are reinforced or cancelled, thus giving a more accurate color reproduction. The effect is particularly visible when looking at a back-lit or silhouetted subject, where more color and detail can clearly be seen in the shadowed areas of the bird.
• Silver Alloy – a high-reflectivity prism coating that acts as a mirror - thus providing both sharper colors and crisper images when compared to aluminum prism coatings. A silver alloy typically has a reflectivity of 95-98%.

To learn about Optical Coatings, click here.