Optolong CLS Light Pollution Filter

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  • Regular price $55.00

Available to Order, usually 7-10 days to ship.

  • Suitable for color CCD cameras and unmodified DSLRs
  • CLS with wider pass-band than UHC and hence is more favorable when observing under mild to moderate light pollution

The CLS (City Light Suppression) broadband filter is designed to improve the visibility of various deep sky objects by selectively reducing the transmission of wavelengths of light pollutants.  Specifically, it reduces those produced by artificial lighting, including mercury vapor lamps, both high & low pressure sodium vapor lights, and the unwanted natural light caused by neutral oxygen emission in our atmosphere (i.e. skyglow).

The CLS filter is highly transparent in main nebula emission lines at OIII (496nm and 500nm), H-beta (486nm), NII (654nm and 658nm), H-alpha (656nm) as well as SII (672nm).  It enhances the contrast and details for both visual and photographic purposes in non-rural areas.

Main Use and Performance

  • Suitable for color CCD cameras and unmodified DSLRs
  • CLS with wider pass-band than UHC and hence is more favored when observing under mild to moderate light pollution
  • Light pollution filters do not eliminate the effects of light pollution or increase the object’s brightness. In many cases, they increase the contrast between nebula and night sky, without brightening the nebula.

    Technical Data

    • Schott substrate material
    • Thickness 2.0mm (1.25”/2”/36mm)
    • Thickenss 1.0mm (clip series)
    • Surface Quality: 60/40 (Refer to MIL-O-13830)
    • Optically polished to ensure accurate 1/4 wavefront and <30 seconds parallelism over both surfaces
    • 95% transmission of the main nebula emission lines (i.e. H-alpha 656nm, OIII 496nm and 500nm, SII 672nm and H-beta 486nm)
    • 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), where a high optical density value indicates very low transmission, and low optical density indicates high transmission.

    Coating Parameter

    • Non-cemented 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 minimizes vignetting by maximizing possible clear aperture (clear aperture is 26mm for 1.25”; 45mm for 2”)
    • Aerometal Material
    • Precise CNC Machining
    • Sand Blasting Process
    • Black Anodized Finish
    • Extinction Treatment to Prevent Reflection
    • Laser Engraving No Fading


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


    • Standard 1.25”
    • Standard 2”
    • Round 36mm Unmounted
    • Clip filters for Canon EOS crop sensor and full frame DSLRs
    SKU: 11801