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The Optolong CLS filter is perfect for both visual and photographic applications in areas that suffer from artificial light pollution. Since the City Light Suppression Filter has a wider pass-band than the popular UHC, or Ultra High Contrast filter, many amateur astronomers favor its use when observing in mild to moderate light pollution. The CLS filter selectively reduces the transmission of light pollution wavelengths, especially artificial light pollution caused by 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 filter cell that will produce a clear aperture of 26mm.
Transmission Characteristics of CLS Filter
Quality Filter Materials:
Optolong Filter Manufacturing Processes and Parameters