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.
The Chroma 1.25-inch H-alpha 3nm Narrowband Filter is essential for imaging objects, like nebulae, that are rich in ionized hydrogen atoms. These line emission filters work extremely well in heavy light polluted areas and allow you image on nights when the moon is up.
Chroma manufactures the highest quality astronomy filters with durable, sputtered hard coating using single substrates of the best glass, eliminating the need for laminations. All primary filter coatings are applied on the front surface and anti-reflection coatings on the rear surface to prevent ghosting and to maximize transmission.
Highly precise and accurate, the pass-bands of these filters remain spectrally stable and do not drift in response to extreme temperature fluctuations or changes in humidity.