ZWO 31mm OIII 7nm Unmounted Narrowband Filter

ZWO 31mm OIII 7nm Unmounted Narrowband Filter

  (1 Review)
✓ 2 year warranty


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About this product

Model:  zwo_oiii_31-7nm
Part Number:  ZWO-OIII7nmD31

New & Improved with higher light transmission and less reflection (reduced halos around bright stars). 

Passes 7nm bandwidth of light centered on a 500nm wavelength, which corresponds to OIII emission lines. All other light is blocked.

Adding a ZWO O-III Narrowband filter to your imaging collection will take you beyond RGB imaging and reveals your favorite nebulas in a totally new light, no matter how polluted your skies may be! 


  • FWHM: 7±0.5nm
  • Glass Thickness 2.0+/-0.03 mm (1.25”/31mm/36mm)
  • Fine-optically polished glass ensures accurate 1/4 wavefront over both surfaces
  • Approx 90% transmission at major OIII line 500nm
  • Infrared wavelength 700-1100nm cut-off
  • <0.1% transmission of off-band, OD3 (Optical Density)

Transmission Curve

Customer reviews

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Not perfect but near enough.
10 October 2019  | 

When used in a filterwheel with the complete single washer type fixing, these filters are really good. Havenít tried a target with a very bright in field yet for the O and S filters, but the H does give a halo . The O filter is slightly off focus from the H and S. But for the price I forgive the minor shortcomings.


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