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Cyclops Optics

Optolong CLS Clip-On Filter

Discontinued. Please refer to CLS-CCD

Optolong CLS Clip-On Filter

Discontinued. Please refer to CLS-CCD
Shipping Weight:
0.10 KGS
Typically ships in 24 hours

Product Description

Optolong CLS (City Light Suppression) is a dual-bandpass filter which selectively enhances emission from nebulas and suppresses the transmission of light pollution sources. CLS enhances the contrast of nebulas and reduce background brightness mostly dominated by light pollution. It has wider passband than UHC (Ultra High Contrast) and thus it enhances deep sky objects under mild to moderate light pollution yet offering a more balanced colour rendition.

CLS selectively cuts out light pollution emission. For example, mercury vapor lamps, high and low pressure sodium vapor lights and skyglow caused by emission from neutral oxygen in our atmosphere. Among the emission lines enhanced are OIII (496, 500nm), H-beta (486nm), NII (654, 658nm), H-alpha (656nm) and SII (672nm).  



  • 95% transmission at major nebula emission lines
  • 0.1% transmission* at off-band at Na (589nm), Hg (435nm, 578nm). 
  • Multi-layers anti-reflection coating
  • Precise and sharp roll-off at light pollutant lines
  • 2 mm filter thickness (1.25", 2" and 77mm) | 1mm (clip series)
  • Made on Schott substrate
  • Finely polished to 1/4 wave accuracy
  • Surface quality: 60/40 (MIL-O-13830 standard)

*equivalent to OD3 


Recommended applications

  • Monochrome & one-shot-colour CCD/CMOS camera
  • Deep sky colour imaging, particularly emission nebula or DSO emitting in the H-alpha, H-beta, O-III and S-II lines 

Available in sizes

  • 1.25" (26mm clear aperture)
  • 2" (45mm clear aperture)
  • Clip-on filter for Canon EOS APS-C and Full Frame
  • Clip-on filter for Nikon APS-C and Full Frame

Coating technologies

  • Multi layers anti-reflection coating
  • Non cementing optical substrate coating
  • Electron-beam gun evaporation with ion-assisted deposition coating technology to enhance coating durability and resistance to scratching as well as stability on central wavelength such that passband does not deviate with temperature change
  • Planetary rotation system offers high precision and homogeneity of coating surface ensuring high value on passband transmission and off-band blocking. 

Filter cell technologies

  • CNC machined with aerospace grade aluminium
  • Black anoidised finish and extinction treatment to prevent refection
  • Laser engraved fade-free wordings 

We care about delivering your filter in perfect form and thus every Optolong filter sits on a high density sponge carton lining and packaged in highly rigid plastic PP case with high pressure EVA case lining. 

User gallery


Author: Wei Guo @ October 2015, XuYi, Jiangsu, China
Camera: QHY8L
Optics: Skyrover 80 APO
Filter: Optolong CLS-CCD


NGC7635 & SH2-157
Author: Wei Guo @ October 2015, XuYi, Jiangsu, China
Camera: QHY8L
Optics: Skyrover 80 APO
Filter: Optolong CLS-CCD 

About Optolong

Optolong is a brand dedicated for astronomical filters R&D and production under Kunming Yulong Optical & Electronics Technology Co. Ltd. Yulong is a professional manufacturer of high quality filters since 1999. Yulong has passed ISO9001 quality certifcation and all products meet ROHS standard authorised by SGS test. 

Their major equipment include ultra clean room, five precise vacuum coating machines, Shimadzu UV-VIS-NIR spectrophotometer, 12 sinks ultrasonic cleaning machines and grinding/rolling/cutting machines.

Optolong filters only use the best glass — German's Schott glass as the substrate which has an industry leading level of flatness which is crucial to minimise the occurence of halo and ensure high quality image.