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The Altair Astro Premium Sii 6.5nm filter is designed for astro imaging of nebulae with Mono CCD or CMOS cameras, blocking light pollution by cutting out the light pollution wavelengths. The filter blocks UV IR and has an anti-reflection AR coating.
Buying the full SHO set allows significant cost savings as opposed to purchasing the filters separately.
A 6.5nm to 7nm FHWM gives higher contrast compared to say 12nm FHWM filters for better performance within heavily light-polluted urban areas, and higher contrast for imaging faint objects. The emission lines of artificial lighting (mercury (Hg) and sodium (Na) as well as skyglow are completely suppressed, allowing for long exposures in urban conditions. LED lighting outside the Oiii bandpass is also blocked.
Steep transmission curves with narrow pass-bands give high image contrast. Advanced UV/IR blocking coatings give small star sizes even with refractor optics.
AR (Anti Reflection) coatings suppress halo effects and internal reflections for more pleasing star images. Ultra-flat BK7 glass housed in a precision CNC machined filter cell for strain-free mounting, and freedom from tilt. Filters are 1.85 mm thick, 1/4 wave flatness, with ≤30 arc seconds parallelism.