The CLS Light Pollution Filter - 50mm Square Unmounted by Astronomik:

The Astronomik CLS is a light pollution reduction filter for black & white and color imaging of nebulae, galaxies and star clusters. 

The Astronomik CLS blocks the light of the spectral lines of mercury and sodium-vapor lamps and lets the largest part of the visible light and H-alpha emissions pass. All the important emission lines, as well as the spectral region that the very well dark adapted eye can see, can pass through the filter.

Optimized for telescope or binoculars with apertures between 6 and 30 inches making it an excellent choice for most users. If you have a smaller aperture telescope, consider the 1.25-inch filter instead which will be a more compatible for telescopes between 3.75 and 18.75-inches.

The Astronomik CLS Light Pollution Filter is good for use under both dark and urban skies for reducing light pollution made by mercury-vapor lamps. For film photography and modified DSLR use, the CLS filter gives good performance and near perfect color balance. While this filter does perform well with webcam and video equipment under light polluted skies, it is not suitable for planetary use.

Astronomik CLS Light Pollution Filter - 50mm Square Unmounted Features:

• 92-percent transmission at 486nm (H-beta)
• 92-percent transmission at 496nm (OIII)
• 92-percent transmission at 501nm (OIII)
• 97-percent transmission at 656nm (H-alpha)
• Pass from 450 to 540nm and beyond 650nm
• Parfocal with other Astronomik filters
• Glass thickness: 1mm
• Completely resistant against high humidity, scratches and aging effects
• Diffraction limited, the filter will not reduce the optical performance of your telescope!
• Astronomik filters are delivered in a high-quality, long lasting, filter box

OPT Product Number: AK-CLS-50SQ