ZWO SII Narrowband Filter, 2 Inch, 7nm FWHM, 672nm Wavelength, for Nebula Astrophotography and CCD Imaging

NARROWBAND FILTER: The ZWO SII 7nm 2" filter boosts contrast between celestial objects and the night sky, reducing skyglow and artificial light interference. IDEAL FOR NEBULA IMAGING: Passes light at a 672nm wavelength and is best suited for emission nebulae, planetary nebulae, and supernova remnants. TRICOLOUR ASTROPHOTOGRAPHY: When combined with H-alpha and OIII filters, this SII filter is perfect for tricolour CCD astrophotography sessions. HIGH TRANSMISSION QUALITY: Fine-optically polished to 1/4 wavelength accuracy, with approximately 90% transmission and off-band transmission of less than 0.1% (OD3). FILTER SPECIFICATIONS: Filter size 2", mechanical thickness 7.5mm, thread M48.5x0.75 male, FWHM 7±0.5nm, and infrared cut-off at 700–1100nm.