Nearly three decades ago, a handful of employees left their jobs at Omega Optical and founded Chroma Technology in Vermont. Since then, the company, which is entirely owned by its roughly 150 employees, has evolved into a leading manufacturer of precise optical filters that sport state-of-the-art thin-film coatings. These high-quality filters are a mainstay in the biological life sciences, agriculture, security, and aerospace industries. But of particular interest to
Astronomy readers are Chroma’s superb filters for astronomical imaging. And, because you can buy Chroma filters directly from the company, the prices are also reasonable.
An exceptional coating
One of the best features of Chroma filters is their coating. The company applies a primary coating to the front surface of all their filters, as well as an anti-reflection coating on the rear surface that prevents ghosting and maximizes light transmission. When you look at a Chroma filter, the front side is highly reflective, while the back side appears completely transparent. Chroma’s standard filters can be used in optical systems as fast as f/4. Or, you can order special filters for systems as fast as f/2. Either way, Chroma offers them all in the standard sizes: 1.25-inch and 2-inch round, and 50-millimeter square.
Unlike the filters from many other companies, Chroma makes theirs by first coating 8-inch squares of optical-quality glass before they cut the filters to the desired size and shape. This ensures the coating is as even as possible, right to the very edge of the filter. (Filters cut before coating frequently have a thinner coat at the edge, due to the filter resting on a support during the coating process.) Finally, to prevent reflections and seal the outside of the coated and cut filter, a black edge is applied.
Chroma filters use optical interference coatings to ensure that only the right light passes through. These coatings get their unique microstructure thanks to a specific arrangement of layered materials that have different refractive indices. This helps interference coatings efficiently transmit the light you want, while blocking the light you don’t.
