The Optolong CLS (City Light Suppression) broadband filter is designed to improve the visibility of various deepsky objects. By selectively reducing the transmission of wavelengths of light pollutants, specifically those produced by artificial lightings 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).

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 both visual and photograghic purpose at sub-rural area.

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 filter 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, not brightening the nebula.

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 minimize vignetting by maximize 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