Please Note: The interference coatings that optical filters are made with are angle-sensitive and shift to the blue with fast focal ratios. This is not a problem for filters 5nm or wider, but the 3nm filters shift enough to compromise transmission at the wavelength line of interest. Chroma has made a set of Ha, OIII and SII 3nm that are optimized for F/3 beams by moving the center wavelength slightly into the red so they will shift slightly to the blue when used in an F/3 beam, thus maximizing transmission at the nominal wavelength. For beams faster than F/3, we recommend using 5nm-wide or wider bands.

This Narrowband filter by Chroma is expertly designed for a precise, limited wavelength acceptance of 3nm for SII. 

Built for fast telescopes and equipment able to fit 50x50mm filters.

• Made in America
• Filter sizes up to 2-inch & 50mm Square without T-thread or SCT thread come with a complimentary TPO Filter Case (OS-CF2) to keep your filter safe.
• Built for fast telescopes and equipment able to fit 50x50mm filters.