The Chroma H-alpha 8 nm 31 mm Unmounted (SKU: CT-27003-31D) is a narrowband filter designed for astrophotography of emission nebulae, compatible with filter wheels and unmounted systems. With an 8 nm bandwidth, it offers high light transmission while maintaining good H-alpha selectivity.

Key features

• bandwidth of 8 nm for the H-alpha line (approx. 656 nm)
• bandwidth transmission at approximately 99%
• hard coatings applied using the reactive magnetron sputtering method – resistant to moisture and temperature changes
• anti-reflective coatings on the back surface reduce reflections and ghosting
• all Chroma Astronomy filters are parfocal to each other
• dedicated to optical systems with a f/4 aperture and slower
• the filter is not suitable for observing the Sun

Set components

• H-alpha filter 8 nm 31 mm unmounted – CT-27003-31D

Technical parameters

• type: narrowband H-alpha filter for astrophotography
• diameter: 31 mm, unframed
• bandwidth: 8 nm
• central wavelength (CWL): approx. 656 nm
• transmission: approx. 99%
• optical substrate: 3.0 mm thick glass
• coating technology: reactive magnetron sputtering (hard coatings)
• coating construction: main layer on the front side, AR coatings on the back side
• Transmitted wavefront accuracy: better than 0.25 waves/inch
• parfocal: yes (with other Chroma Astronomy filters)
• production: USA (Vermont)