Altair ColourPRO ULTRA

3nm HSO Narrowband Filter Set (2") — Certified

This is the “go image in the city anyway” narrowband set. The Altair ColourPRO ULTRA 3nm HSO kit gives you ultra-tight 3nm bandpasses for maximum contrast on emission nebulae, plus aggressive out-of-band blocking and halo suppression coatings so bright stars behave. And Altair doesn’t just tell you it’s in spec—each filter includes its own spectrographic test report so you know exactly what you’re getting.

• Complete HSO 3-filter set in 2" at a discounted bundle price
• Built for mono CMOS nebula imaging (strong light-pollution rejection)
• Individually certified: each filter includes a high-resolution spectrographic report confirming tolerance
• 3nm FWHM for higher contrast than wider 6nm filters—especially in heavy urban light pollution
• Designed to suppress common artificial lighting emissions (Hg/Na) and natural skyglow
  • Also blocks LED lighting outside the bandpass
  • Users report viable imaging even in extremely bright skies (up to Bortle 9) and sometimes slightly outside astronomical darkness (within reason)
• OD7-class blocking (average between 200–1100nm) for ultra-high contrast on faint targets
• UV/IR blocking helps keep stars tighter (reduces refractor bloating)
• V3R anti-reflection / anti-halo coatings
  • Strong halo suppression and reduced internal reflections
  • Increased transmission (about +2.5% vs prior coating), with ~92% average across the batch and no filter below 90%
• Best performance on f/3.5 or slower optics
  • Faster than f/3.5 can still work, but with reduced contrast and possible artifacts
• Premium substrate and cell for flatness and mechanical stability
  • Ultra-flat quartz glass in a precision CNC machined cell (strain-free mounting, minimizes tilt risk)
  • SiO2 hard overcoat for easier cleaning with common optical cleaners

Specifications

• Filter type: Narrowband HSO set (3 filters)
• Size: 2" mounted
• FWHM: 3nm
• CWL / FWHM tolerance: 0.5nm
• Transmission (target wavelength): approx. 95% (± 3% across batch)
• Average transmission (batch): ~92%; no filter < 90%
• Blocking: OD7 average from 200nm to 1100nm (~0.00001% leakage)
• Coatings: V3R anti-reflection / anti-halo + UV/IR blocking
• Substrate: Ultra-flat quartz glass
• Glass thickness: 1.85mm
• Flatness: 1/4 wave
• Parallelism: 30 arc seconds
• Cell: Precision CNC machined (strain-free mounting)
• Overcoat: SiO2 tough overcoating (cleaning-friendly)
• Recommended optics speed: f/3.5 or slower (faster systems may reduce contrast / introduce artifacts)

What’s in the box?

• Altair ColourPRO ULTRA 3nm HSO Narrowband Filter Set (2") — 3 filters
• Individual spectrographic test report for each filter (certification)

Software and Docs

• Spectrographic certification reports (included per filter)
• No additional software required (standard filter wheel/camera compatible)