Optolong CLS (City Light Suppression) broadband filter is designed to improve the visibility of various deepsky objects.
The CLS (City Light Suppression) broadband filter is designed to improve the visibility of various deepsky objects.
  • Description

  • Specification

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 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.


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. Coating Technology

·Multi-layers anti-reflection coating

·Non-cementing optical substrate coating

·Optolong 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.




4. Optolong CLS Gloable Price


         CLS filter MAP           Unit Price in USD dollars      
1.25" mounted $55.00
2" mounted  $85.00





5. Packing

Outer Box: silve box

Plastic Box: PP material

Lining: imported high pressure white EVA material



6. Optolong CLS Performance

I.  California nebula NGC1499 © Oliver Smie (Germany)  

The picture result from California nebula NGC1499 with Optolong CLS filter.
- camera Sony A7Sa (modified, no short pass filter)
- total 80min exposure time
- 130mm F/5 Newton + coma corrector



Warm prompt

●About color: due to the influence of ambient light, color difference of the display and flash photography, the color of the product may have some color difference. Detailed color is in accordana with the final product.

●About coating: the interference filter will show different colors under different light, which is a normal phenomenon. Please refer to the material object.

●About the style: in order to improve the product, the change of design/appearance/parameters has not been updated in time. Please see the subject produce.

●About the description: the series of this product have the same material, technology and design, different sizes only, please note.


Optolong CLS feature:

⭐1.25"(1 1/4"), 2" for eyepiece