The Optolong CLS-CCD (City Light Suppression) broadband filter is designed to improve the visibility of emission deep sky objects.

Different from the Optolong CLS filter, the Optolong CLS-CCD cuts off the infrared radiation between 700-1100nm (IR/UV Cut).  It works with astronomy cameras and modified DSLR’s for astrophotography.

It selectively reduces the transmission of wavelengths of artificial light, specifically those produced by mercury vapour lamps, both high and low pressure sodium vapour lights and the unwanted natural light caused by neutral oxygen emission in our atmosphere (i.e. skyglow).

Compared to the UHC filter, the CLS-CCD has a wider bandpass so it is preferred in areas with mild to moderate light pollution. It rejects the typical wavelength associated with artificial light and it is highly transparent in the main emission nebula lines: OIII (496nm and 500nm), H-beta (486nm), NII (654nm and 658nm), H-alpha (656nm) as well as SII (672nm).

For astronomy cameras it needs to be used in combination with an IR/UC cut filter. Alternatively it can be used the CLS-CCD filter that cuts off the infrared and ultraviolet wavelengths. In DSLR’s the IR/UV filter is embedded in the camera so the standard UHC filter is sufficient.

Light pollution filters do not eliminate the effects of light pollution or increase the object’s brightness, instead they increase the contrast between objects and the night sky.