The CLS (City Light Suppression) broadband filter is designed to improve the visibility of various deepsky objects.
 
DESCRIPTION
The 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
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.
 
WARNING
The filters of Optolong are not designed for sun observation. DO NOT LOOK AT THE SUN WITH OPTOLONG FILTER. You would be BLIND if you fail to observe the warning.
 
TECHNICAL DATA
Sbustrate: Optical glass
Thickness: 1.85mm
Tave:  T>90%
Blocking range: 400-700nm
Blcoking depth: light pollution  line blocking >99%
Surface quality: 60/40
Transmitted Wavefront RMS: λ/4
Parallelism: 30s

How to read the chart?
The horizontal axis is the Wavelength in Nanometers(nm).
The vertical axis is transmission in %.
The RED line shows the transmission of the CLS filter. Green line shows the emmission of nebula. The artifical emission lines are shown in ORANGE. 

COATING TECHNOLOGY
Multi-layers anti-reflection coating
Non-cementing optical substrate coating
Optolong L-Pro filter adopts precision coating based on 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.
 
PACKING
Outer Box: silve box
Plastic Box: PP material
Lining: imported high pressure white EVA material