What are the differences between the optical coatings?

Optical coatings reduce internal light loss and glare and ensure even light transmission, resulting in greater image sharpness and contrast. When you have your optics coated, your glass will have a less shiny, even dark appearance when looking into the barrel or tube. The glass may provide a greenish, bluish, or brownish tint due to the magnesium fluoride or calcium fluoride they are made from. This coating destructively interferes with certain colors or wavelengths of light, eliminating their reflection. Therefore, more light enters your optics and can pass through to your eyes.

Almost all modern consumer optics have at least some kind of coating elements, though there are different levels and qualities of coatings. Celestron has different levels of coating for optical tubes, binoculars, and spotting scopes. Here are the different coatings Celestron has on our products:

Coated: At least one of the major optical elements has a coating on at least one surface.

Fully Coated: All lenses and glass surfaces have a coating layer. For binoculars, this includes the long side of the prism.

Multi-Coated: At least one of the major optical elements in a fully-coated binocular has multiple coatings of anti-reflective compounds on at least one surface

Fully Broadband Multi-Coated: Predominately found in our binoculars and spotting scopes. Fully Broadband Multi-Coated decrease surface reflectivity therefore allows greater optical through-put across the entire visible light spectrum. Fully broadband multi-coated optics feature these types of coating on all optical surfaces throughout the entire instrument.

Fully Multi-Coated: All glass surfaces have multiple coatings and it is the best kind, resulting in light transmission of 90-95% for bright, sharp and contrast images.

Fully Multi-Coated XLT Coating: Only found in certain binoculars and spotting scopes (SkyMaster Pro and Echelon binoculars,TrailSeeker and Regal M2 Spotting Scopes). Fully Multi-Coated XLT Coating is an adapted form of Celestron’s proprietary StarBright XLT coatings. Celestron’s XLT coating further decreases reflectivity in fully multi-coated optical systems for higher optical throughput across a broad range of the visible light spectrum.

StarBright XLT: Predominately found in our telescope Schmidt Cassegrain optical tubes and the larger spotting scopes (C5, C90, and C70), the StarBright XLT coating outperforms any other coating in the commercial telescope market. The three major components that make up our StarBright XLT design is the Unique enhanced multi-layer mirror coatings, multi-layer anti-reflective coatings, and high-transmission water white glass.

NOTE: Some roof prism binoculars feature phase coatings because the light travelling through the roof prism assembly can diverge by wavelength as it transits the prism and emerge out of phase, thus producing a “muddy,” lower contrast image. By applying a special coating that compensates for this divergence, the contrast loss is eliminated, giving phase-coated binoculars brighter and more vivid images. Phase coatings are not applied to Porro prism binoculars as they are not necessary due to the more simple optical path through the prisms.

For information on Prism coatings, click here.