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CLS filters are broadband filters, which means they allow wide incident light wavelength ranges to pass through. They block light only in selected sections of the spectrum. These blocked sections are chosen in such a way that they coincide with the emissions from artificial light sources. In addition to artificial sources, there are also natural sky brightness phenomena, which are also blocked by CLS filters. Ultimately, the sky background appears darker with a CLS filter. The object being observed stands out more clearly against the background.

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Omegon Filters Pro 2'' CLS filter
Omegon
Filters Pro 2'' CLS filter
$ 99.00
ready for shipping in 24 h
Omegon Filters Nebula/ city light filter 1.25 ''
Omegon
Filters Nebula/ city light filter 1.25 ''
( 3 / 5 )
$ 39.90
ready for shipping in 24 h
Omegon Filters Light Pollution Filter, 2”
Omegon
Filters Light Pollution Filter, 2”
( 3.33 / 5 )
$ 59.00
ready for shipping in 24 h
Omegon Filters 1.25'' deep sky filter
Omegon
Filters 1.25'' deep sky filter
$ 89.00
ready for shipping in 24 h
Omegon Filters Pro 1.25'' CLS filter
Omegon
Filters Pro 1.25'' CLS filter
$ 69.00
ready for shipping in 24 h
Omegon Filters 1.25'' Clear Sky filter
Omegon
Filters 1.25'' Clear Sky filter
$ 129.00
ready for shipping in 24 h
Optolong Filters L-Pro 2''
Optolong
Filters L-Pro 2''
$ 220.00
ready for shipping in 24 h
Optolong Filters L-Pro 1.25''
Optolong
Filters L-Pro 1.25''
$ 168.00
ready for shipping in 24 h
Optolong Filters Clip Filter for Canon EOS APS-C CLS
Optolong
Filters Clip Filter for Canon EOS APS-C CLS
Our price:
RRP:  $ 105.00
$ 84.00
ready for shipping in 24 h
Optolong Filters Filter L-eNhance 1.25
Optolong
Filters Filter L-eNhance 1.25
$ 199.00
ready for shipping in 24 h
Optolong Filters Clear Sky Filter 82mm
Optolong
Filters Clear Sky Filter 82mm
$ 231.00
ready for shipping in 24 h
Optolong Filters Clear Sky Filter 77mm
Optolong
Filters Clear Sky Filter 77mm
$ 178.00
ready for shipping in 24 h
IDAS Filters LPS-P2 ungefasst 36mm
IDAS
Filters LPS-P2 ungefasst 36mm
$ 189.00
ready for shipping in 24 h
IDAS Filters LPS-D3-48/NGS1-48
IDAS
Filters LPS-D3-48/NGS1-48
$ 346.00
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IDAS Filters Night Glow Suppression ZWO ASI
IDAS
Filters Night Glow Suppression ZWO ASI
$ 378.00
ready for shipping in 24 h
Optolong Filters Clip Filter for Canon EOS FF L-Pro
Optolong
Filters Clip Filter for Canon EOS FF L-Pro
Our price:
RRP:  $ 368.00
$ 251.00
ready for shipping in 24 h
STC Filters Astro Multispectra Filter 2"
STC
Filters Astro Multispectra Filter 2"
$ 368.00
ready for shipping in 24 h
Chroma Filters LoGlow Light Pollution 1.25"
Chroma
Filters LoGlow Light Pollution 1.25"
$ 530.00
ready for shipping in 3-5 weeks
Optolong Filters Clip Filter for Canon EOS APS-C CLS-CCD
Optolong
Filters Clip Filter for Canon EOS APS-C CLS-CCD
Our price:
RRP:  $ 136.00
$ 101.00
ready for shipping in 24 h
Chroma Filters LoGlow Light Pollution 2"
Chroma
Filters LoGlow Light Pollution 2"
$ 930.00
ready for shipping in 24 h
Astronomik Filters CLS Clip Nikon Z XL
Astronomik
Filters CLS Clip Nikon Z XL
$ 210.00
ready for shipping in 1-2 weeks
IDAS Filters Night Glow Suppression Canon EOS APS-C
IDAS
Filters Night Glow Suppression Canon EOS APS-C
$ 378.00
ready for shipping in 3-5 weeks
Optolong Filters L-Ultimate 3nm 2"
Optolong
Filters L-Ultimate 3nm 2"
$ 420.00
ready for shipping in 24 h
Astronomik Filters CLS CCD 50mm filter, mounted
Astronomik
Filters CLS CCD 50mm filter, mounted
$ 241.00
ready for shipping in 1-2 weeks
Astronomik Filters CLC Canon EOS clip filter APS-C
Astronomik
Filters CLC Canon EOS clip filter APS-C
$ 136.00
ready for shipping in 24 h
Explore Scientific Filters 1.25" CLS filter
Explore Scientific
Filters 1.25" CLS filter
$ 61.00
ready for shipping in 1-2 weeks
Astronomik Filters CLS Sony Alpha Clip filter
Astronomik
Filters CLS Sony Alpha Clip filter
$ 210.00
ready for shipping in 24 h
Astronomik Filters CLS CCD XL Clip Canon EOS R
Astronomik
Filters CLS CCD XL Clip Canon EOS R
$ 262.00
ready for shipping in 1-2 weeks
Explore Scientific Filters 2" CLS filter
Explore Scientific
Filters 2" CLS filter
$ 88.00
ready for shipping in 1-2 weeks
Astronomik Filters CLS XL Clip Canon EOS R
Astronomik
Filters CLS XL Clip Canon EOS R
$ 210.00
ready for shipping in 24 h
Astronomik Filters CLS CCD EOS M Clip filter
Astronomik
Filters CLS CCD EOS M Clip filter
$ 168.00
ready for shipping in 1-2 weeks
Astronomik Filters CLS XT Clip Canon EOS APS-C
Astronomik
Filters CLS XT Clip Canon EOS APS-C
$ 157.00
ready for shipping in 24 h
Astronomik Filters CLS Canon EOS M Clip filter
Astronomik
Filters CLS Canon EOS M Clip filter
$ 147.00
ready for shipping in 1-2 weeks
Astronomik Filters CLS CCD EOS clip filter
Astronomik
Filters CLS CCD EOS clip filter
$ 168.00
ready for shipping in 24 h
Astronomik Filters 2" CLS CCD filter
Astronomik
Filters 2" CLS CCD filter
$ 241.00
ready for shipping in 24 h
IDAS Filters LPS-D3 Drop-In Canon EF FullFrame
IDAS
Filters LPS-D3 Drop-In Canon EF FullFrame
$ 420.00
Product can be shipped as of 16.12.2022

The figure below illustrates the principle using the example of the NGS1 filter from IDAS. The black transmission curve shows which wavelength ranges the filter allows to pass through. 100% would mean no filter effect at all. The transmission curve also shows which light wavelength ranges are blocked by the filter. These ranges are associated with the emissions from sodium-vapour lamps and other disruptive light sources. The CLS filter filters out this unwanted light.

The CLS filter allows broad ranges to pass through and is therefore also suitable for small optics.

CLS Transmissionskurve