Optolong CLS Filter 1.25" Mounted - Light Pollution Reduction for Astronomy & Astrophotography - Perfect for DSLR & Telescope Night Sky Photography

Optolong's 1.25" City Light Suppression Filter is perfect not only for visual observations but for astro-imaging as well. This CLS filter is the ideal accessory if you're viewing in an area with artificial light pollution. Due to the CLS Filter's larger pass-band, many amateur astronomers prefer the CLS filter when observing in mild to moderate light pollution. The CLS filter selectively blocks transmission of wavelengths known for light pollution, especially artificial light pollution from high and low-pressure sodium vapor and mercury vapor lights. Using a CLS filter will even help reduce skyglow caused by naturally occurring neutral oxygen emissions in our atmosphere.

The Optolong 1.25” CLS Filter is made Schott glass that has been multi-coated with ion-assisted deposition technology to ensure scratch resistance and stability on the central wavelength, or CWL. The filter cell is made of lightweight, strong metal and is CNC machined, sand-blasted, black anodized, and then laser engraved. The result is a super thin 2" filter cell that will produce a clear aperture of 26mm.

Transmission Characteristics of CLS Filter

• 95% transmission H-Beta 486nm

• 95% transmission OIII 496nm and 500nm

• 95% transmission H-Alpha 656nm

• 95% transmission SII 672nm

• 0.1% transmission Hg at 435nm and 578nm

• 0.1% transmission Na at 589nm

Quality Filter Materials:

• Schott B260 substrate material from Germany, 1.0mm thick

• CNC machined and black anodized aero-metal filter cell that is ultra-thin to provide largest clear aperture; Laser-engraved to prevent fading

• Multiple layers of anti-reflection non-cementing coatings applied via electron-beam gun evaporation with Ion-assisted deposition

Optolong Filter Manufacturing Processes and Parameters

• Filter substrate is fine-optically polished to 1/4 wave and <30 parallelism over both surfaces

• Surface quality, according to MIL-O-13830, is 60/40

• Main nebula emission lines has a transmission of 95%

• Off-band (major emission lines of artificial light pollution) transmission is 0.1%

• High-value transmission of pass-band and optical density of off-band is assured through Optolong’s planetary rotation system, a homogeneous and precise coating procedure

• Each filter comes with a plastic case with high-pressure EVA case lining

• Thin metal cells have a clear aperture of 26mm for 1.25” filters

About Optolong

Optolong is the Astronomy Filters division of Yulong Optics, an optical filter design, and processing company out of Kunming, China that has provided filters for over 700 optical companies since 1999. All Optolong filters pass European Union RoHS requirements and have been certified by TUV Rheinland and Bureau Veritas.