Baader Filters H-alpha/OIII/SII CMOS Ultra-Narrowband 31mm (70901)

H-alpha Filter
The H-alpha filter transmits light at a wavelength of 656nm. It is the ideal narrowband filter for H-alpha astrophotography, providing high-contrast imaging and revealing rich nebula details, even in areas with strong light pollution.

OIII Filter
The narrowband O-III 3nm filter is designed for nebula observation. It allows a 3nm bandwidth of light centered on a wavelength of 500nm, corresponding to OIII emission lines, while blocking all other light.

SII Filter
The narrowband S-II 7nm filter passes light at a wavelength of 672nm with a bandpass of 3nm. This filter is designed specifically for nebula photography and is suitable for most emission nebulae, planetary nebulae, and supernova remnants.

If you want to replicate the iconic look of Hubble Space Telescope (HST) images—such as the "Pillars of Creation" in the Eagle Nebula (Messier 16)—the SII filter is an excellent addition to your collection after H-alpha (H-a) and OIII filters. Like the H-a filter, the SII (sulfur) filter operates in the deep red spectrum near 672nm. Using H-a, OIII, and SII filters together enables tri-color narrowband imaging, delivering that signature "Hubble look" for many emission nebulae. These filters also allow imaging during moonlit nights, ensuring your equipment remains active without long delays.

Specifications

• Capacity:

  • Central wavelength: 656.3nm (H-alpha), 500.7nm (OIII), 671.7nm (SII)

  • Half-value width: 3.5nm (H-alpha), 4nm (OIII & SII)

• Frame:

  • Type: Ring

  • Mount material: Aluminium

  • Coating: Reflex-Blocker™

• Compatibility:

  • Suitable for systems with f/10 to f/3.5

  • Filter thickness: 2mm

  • Filter size: 31mm

• General Information:

  • Type: Filters

  • Build type: Line filter

  • Series: Ultra-Narrowband

• Applications:

  • Useful for photography: Yes

  • Visually useful: No

  • Twin stars: No

  • Moon & planets: No

  • Nebulae & galaxies: Yes