Optolong CLS-CCD Light Pollution Filter

Optolong CLS-CCD Light Pollution Filter

  (3 Reviews)
✓ 2 year warranty


1x in stock shipped 1-2 working days

About this product

Model:  opt_cls-ccd_1.25
Part Number:  11901

City Light Suppression (CLS) CCD Filter - Block Common Light Pollution Sources

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

Together with the 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), the filter is suitable for enhancing the contrast and details for astrophotography.

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! 


  • In addition to the standard CLS filter this also blocks the infrared wavelength 700-1100nm.
  • 95% transmission of 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)
  • Suitable for use with colour CCD and CMOS cameras and modified DSLRs
  • Works well on most emission nebulae, planetary nebulae and supernova remnants.
  • Noticeable boost in contrast and visibility of the fainter outer detail
  • 1.25" or 2" Mounted Sizes.
  • Supplied in a protective plastic case with EVA foam lining
  • 1mm (Clip Filters) or 2mm (1.25" / 2") 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 - Represents the transmission curve of the CLS-CCD Filter.

Green Line - The Major Emission Lines of Nebulae: H-α (656.3nm), H-β (486.1nm), OIII (495.9nm) and OIII (500.7nm)

Orange Line - The Major Emission Lines of Artificial Light Pollution: Hg / Mercury (435.8nm, 546.1nm, 577nm and 578.1nm), Na / Sodium (598nm, 589.6nm, 615.4nm and 616.1nm)

Technical Data

  • Schott substrate material
  • Thickness 2.0 mm (1.25”/2”/36mm)
  • Thickness 1.0 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 the both surfaces
  • 95% transmission of 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), and a high optical density value indicates very low transmission, and low optical density indicates high transmission.

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


Customer reviews

Average Rating (3 Reviews):  
Write a Review and share your opinions!

Rating (max 5):  
13 December 2021  | 

Arrived following day, well packaged. Only used once so far but light pollution dealt with. Will need more use to compare to other filters but so far, so good

Rating (max 5):  
Improvement on Light polluted skies, but with added downsides
11 September 2021  | 

Firstly, 5 Stars for FLO service. As for the filter, 4 stars because it works really well in its original purpose - it reduces light pollution a lot and allows for 5 times longer exposures from my serverly light polluted skies - meaning I can get a lot of data ... but there is a very slight bloating of stars (when comparing exposures of same length). The bloating is not really bad (seems like a 10% increase in star size), Stacking and post processing removes it, but there's always a chance that it might be effecting the image in some very minor ways.

Rating (max 5):  
Excellent at this price point
22 July 2021  | 

A budget CLS filter that does exactly what it says on the box. I image typically from a Bortle 8 and this filter has cut a large proportion on my light pollution out, it isn't perfect with the newer LED lights but a really good first step for those looking to try and capture nebulae (I have also used it successfully to capture some galaxies too) from a city. Used on a non modded DSLR it really has helped.


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