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Optolong H-Alpha 7nm Narrowband Filter

Optolong H-Alpha 7nm Narrowband Filter
Price:  £129.90
List Price:  £148.00
(Inc. 20% VAT)

Product Code:  OPT-H-ALPHA-7NM-1.25
Brand:  Optolong


This premium Optolong Narrowband H-Alpha filter is designed for nebula observation or CCD/dSLR imaging at 7nm bandwidth of light centered on a wavelength of 656nm, which corresponds to H-alpha emission lines.

This filter will reduce 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). It is a red colored filter. Many images of planetary nebulae and supernova remnants are taken only with H-alpha and OIII filters. They show great structural details, but have natural colors, looking like an RGB image.

Main Use and Performance

Suitable for visual observation through large aperture telescopes or general CCD/dSLR imaging  of most emission nebulae, planetary nebulae and supernova remnants even during full moon and in areas suffering from severe light pollution. Suitable for viewing bright nebulae like M42 Orion Nebula from cities with heavy light pollution.

Images of the Hubble-palette like the famous "Pillars of Creation"  of the Eagle nebula (M16) are taken by the combination of H-alpha, OIII-CCD and SII-CCD filters. Narrowband imaging with a SHO set (H-alpha, OIII-CCD and SII-CCD) can be done with the moon up in a  heavily light polluted area so your equipment won't have to be dormant for several weeks.

A H-alpha filter can also be the first addition to a LRGB set for most imagers who will blend a black-and-white H-alpha image into RGB data to enhance structural detail whilst maintaining natural look.

Bear in mind that light pollution filters do not eliminate the effects of light pollution or increase the object’s brightness. In many cases, they simply increase the contrast between nebula and night sky, but without brightening the 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) and 1.00 mm Clip series
  • 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 H-alpha line 656nm
  • 0.1% transmission of off-band, specifically of 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). 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
  • Clip filter series


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

Optical Coating

  • Multi-layer 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. (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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