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Optolong SII 6.5nm Narrowband Filter

Optolong SII 6.5nm Narrowband Filter
Price:  £119.90
List Price:  £134.00
(Inc. 20% VAT)

Product Code:  OPT-SII-CCD-6.5NM-1.25
Brand:  Optolong


This premium Optolong Narrowband SII filter (Sulphur II for CCD) is designed for CCD imaging of deep sky objects and nebulosity allowing 6.5nm bandwidth of light centered on a wavelength of 672nm through, which corresponds to SII emission lines, and reducing the transmission of certain wavelengths of light, specifically those produced by artificial light including mercury vapor, and both high and low pressure sodium vapor lights and the unwanted natural light caused by neutral oxygen emission in our atmosphere (i.e. skyglow). SII emits at 672nm (to be precise: at 671.6nm and 673.1nm) and it is a red colored filter. Many images of planetary nebulae and supernova remnants are taken with H-alpha, OIII and SII filters (such as the famous “Pillars of Creation”  or M16, Eagle Nebula) They show great structural details, but have natural colors, looking like an RGB image.

Main Use and Performance

Suitable for mainly narrowband imaging of most emission nebulae, planetary nebulae and supernova remnants, but could be also used for visual observations when used with a very large telescope with low focal ratio. Suitable for viewing or imaging of bright nebulae like M42 Orion Nebula in heavy light pollution. When using visually, use it with a very large aperture telescope under clear and dark viewing conditions with good seeing and make sure that your eyes are well adapted to the darkness for the best visual experience.

Light pollution filters do not eliminate the effects of light pollution or increase the object’s brightness. In most cases, they increase the contrast between nebula and night sky, without brightening the nebula.

Use with H-alpha 7nm and OIII-CCD 6.5nm extra narrowband filters (SHO Set) for tricolor CCD astrophotography
Narrowband imaging with SHO set can be done with the Moon up in heavy light pollution, so your equipment is not sitting dormant for several weeks
Hubble look of images can be achieved by the combination of H-alpha, OIII-CCD and SII-CCD, such as the famous “Pillars of Creation” (M16 Eagle Nebula)


Optolong filters are not designed for solar observation. DO NOT LOOK AT THE SUN WITH ANY OPTOLONG FILTER as permanent eye damage will be the result.

Technical Data

  • Schott substrate material
  • Glass thickness 2.0 mm (1.25”/2”/36mm)
  • Surface Quality: 60/40 (Refer to MIL-O-13830)
  • Fine-optically polished to ensure accurate 1/4 wavefront and < 30 seconds parallelism over both surfaces
  • 80% transmission at the SII "line" of 672nm
  • Infrared wavelength 700-1100nm cut-off
  • 0.1% transmission of off-band, specifically the major emission lines of artificial light pollution (i.e. Na 589nm, Hg 435nm and 578nm). Transmission of 0.1% is equivalent to OD3(Optical Density), and a high optical density value indicates very low transmission, and low optical density indicates high transmission.

Filter Cell

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

Available Sizes

  • Standard 1.25” & 2”
  • Round 36mm Unmounted


  • Plastic PP Case
  • Imported High Pressure EVA Case Lining
  • Silver Cardboard Box
  • High Density Sponge Carton Lining

Optical 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. (Please note, "planetary rotation system" is a type of optical coating process and does not refer to the astronomical system describing the motion of the planets in our solar system.)

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