Optolong 6.5nm OIII Narrowband Deep Sky Imaging Filter

Optolong 6.5nm OIII Narrowband Deep Sky Imaging Filter

  (1 Review)
✓ 2 year warranty


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About this product

Model:  opt_oiii_6.5nm_31mm
Part Number:  11503

Latest Version - Higher contrast and coating enhancements.

The Optolong OIII 6.5nm filter allows 6.5nm bandwidth of light centered on a wavelength of 500nm through. This filter does an excellent job of blocking out other wavelengths of light specifically artificial sources of light pollution including mercury vapour, high and low pressure sodium vapour lights and unwanted natural light caused by neutral oxygen emission in our atmosphere (skyglow).

OIII emits 495.9nm and 500.7nm and it is a blue-green coloured filter. Many images of planetary nebula and supernova remnants are taken only with H-alpha and OIII filters. They show great structural details, but have natural colours like an RGB image.

Also suitable for visual observation on most emission nebulae, planetary nebulae and supernova remnants.

IMPORTANT: Filters manufactured by Optolong are NOT designed for observing or photographing the Sun. DO NOT use Optolong filters to observe or photograph the Sun. If you do it will result in permanent eye damage! 


  • 80% transmission at passband / Precision off-band blocking
  • Infrared wavelength 700-1100nm blocked
  • 0.1% transmission of off-band, specifically the major emission lines of artificial light pollution (i.e. Na 589nm, Hg 435nm and 578nm)

  • Suitable for use with mono CCD and CMOS cameras
  • 1.25" / 2" mounted or 31mm / 36mm unmounted sizes.
  • Supplied in a protective plastic case with EVA foam lining
  • 2mm Thick Schott Glass
  • Fine-optically polished on both sides - ensures accurate λ/4 wavefront and <30 seconds parallelism over the both surfaces

Transmission Chart

Red Line: H-alpha, 7nm centred at 656.3nm.

Blue Line: SII, 6.5nm centred at 671.6nm.

Green Line: OIII, 6.5nm centred at 500.7nm

Technical Data

  • Schott substrate material
  • Thickness 2.0 mm
  • Surface Quality: 60/40 (Refer to MIL-O-13830)
  • Fine-optically polished to ensure accurate 1/4 wavefront and <30 seconds parallelism over the both surfaces
  • 95% transmission at passband
  • Infrared wavelength 700-1100nm cut-off

  • Precision off-band blocking

Coating Parameter

  • Multi-layers anti-reflection coating
  • Non-cementing optical substrate coating
  • Electron-beam gun evaporation with Ion-assisted deposition coating technology for durability and resistance to scratching, as well as stability on CWL (central wavelength) no deviation affected by temperature change
  • Planetary rotation system offers precision and homogeneity of coatings ensuring high value on transmission of pass-band and Optical density of off-band

Filter Cell

  • Ultra-thin filter cell minimise vignetting by maximise possible clear aperture (clear aperture is 26mm for 1.25”; 45mm for 2”)
  • Aerometal Material | Precise CNC Machining | Sand Blasting Process | Black Anodised Finish | Extinction Treatment to Prevent Reflection | Laser Engraving No Fading

Sample Images


Customer reviews

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Optolong 6.5nm OIII Narrowband Deep Sky Imaging Filter
27 April 2021  | 

I have only had chance to use this filter once since i got it,but from what i have seen it is exerllent.Imaging M97 the Owl Nebulae displayed a great deal of Oxtgen 111,and with the Moon present i found that impressive.
Its 6.5nm wave length to me hits the sweet spot between the 12nm and the more costly 3nm.
Its seems very well made,and i am certain that i have made the right choice.
I can whole heartedly recommend this O111 Filter.


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