The Chroma O-III 5 nm 50x50 mm Unmounted (SKU: CT-27007-50X50) is a square format narrowband filter designed for professional astrophotography of emission nebulae. The 5 nm band effectively isolates the O-III oxygen line at 500.7 nm, offering high light transmission and improved image contrast.

Key features

• bandwidth of 5 nm in the O-III range (approx. 500.7 nm)
• transmission in the band of approximately 99%
• hard coatings applied using the reactive magnetron sputtering method – durability and stability of optical parameters
• anti-reflective coatings on the back surface reduce 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 intended for observing the Sun

Set components

• O-III filter 5 nm 50x50 mm unmounted – CT-27007-50X50

Technical parameters

• type: O-III narrowband filter for astrophotography
• format: 50x50 mm, unframed
• bandwidth: 5 nm
• central wavelength (CWL): approx. 500.7 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)