The Chroma S-II 5 nm 65x65 mm Unmounted (SKU: CT-27010-65X65) is a large square format narrowband filter designed for the most demanding astrophotography systems. With a 5 nm bandwidth, it effectively isolates the S-II sulfur line at 672.4 nm, offering high contrast and high light transmission, allowing for shorter exposure times and capturing fainter nebula structures.

Key features

• 5 nm bandwidth tuned to the S-II line (approx. 672.4 nm)
• bandwidth transmission at approximately 99%
• hard coatings applied using the reactive magnetron sputtering method – exceptional durability and spectral stability
• anti-reflective coatings on the back surface eliminate reflections and ghosting
• all Chroma Astronomy filters are parfocal to each other
• designed for optical systems f/4 and faster, also suitable for f/3
• the filter is not suitable for observing the Sun

Set components

• S-II filter 5 nm 65x65 mm unframed – CT-27010-65X65

Technical parameters

• type: S-II narrowband filter for astrophotography
• format: 65x65 mm, unframed
• bandwidth: 5 nm
• central wavelength (CWL): approx. 672.4 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)