Optolong CLS (City Light Suppression) broadband filter

1.  Optolong CLS Introduction

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 photographic 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.

2. Optolong CLS Spectrum and Characteristic

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.

3. Packing

Outer Box: silve box

Plastic Box: PP material

Lining: imported high pressure white EVA material