Astronomik CLS CCD EOS Clip FilterThe Astronomik CLS (City Light Suppression) CCD EOS Clip is a great filter against light pollution in a clip design for Canon EOS DSLRs. It blocks emissions of artificial light sources like streetlights and airglow.
It enhances the contrast between our “desired” objects and the background.

92% transmission at 486nm (H-beta),
92% transmission at 496nm (OIII),
92% transmission at 501nm (OIII),
97% transmission at 656nm (H alpha), pass from 450 to 540nm and from 640 to 690nm.


Unfortunately with unmodified DSLR cameras (like my 100D) the images have a strong cyan-blue tint. (check here how to remove it)

Depending on your processing software it is important to do a custom white balance at daylight (noon) with inserted filter and use this profile for astrophotography. For PixInsight it doesn’t matter what type of white balance is used, if DSLR_RAW is set to “Pure RAW”.


Anyway, the results with the filter are far better for heavy light polluted areas.
Convince yourself:

Location: My balcony in Derendingen (454m), Solothurn, Switzerland  – see light pollution map below
Date/Time: 01/04/2016 19:24h CET (shot 1) – 19:27h CET (shot 2)
Camera: Canon EOS 100D
Lens: Canon EF 50mm f/1.4
Tracker: Sky Watcher Star Adventurer

Light pollution 2015, Derendingen, Solothurn, Switzerland
Light pollution 2015, Derendingen, Solothurn, Switzerland
Shot 1: Single sub @ f/3.5, ISO640, 90 seconds
Shot 1: Single sub @ f/3.5, ISO640, 90 seconds
Shot 2: Single sub at the same settings and FOV - and the filter
Shot 2: Single sub at the same settings and FOV – and the filter

Sorry for the fine clouds… the wheater this evening was not excellent.

Check here my recent DeepSkyStacker settings. It removes successfully the cyan-blue tint to a very acceptable level 😀

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  1. Peter Komatovic

    I just found your blog. A very nice one. I’m using a very similar setup with Star Advanturer, EOS 40Da + Astronomik CLS and EF 200 f2.8 II L USM or EF 400 f.5.6 L lense like you have. I dont use an dedicated guider hardware like you but always use my small laptop Transformer T200 and the PHD guiding software. I found some very useful tips on your BLOG so thanks! I wanted to update my old EOS 40Da so I wonder how the 70Da performs in this regard. Some folks says that ISO 400 on EOS 40Da is like ISO 1600 on the 70Da so if this is true then this is great news. Your photos look stunning for this kind of equipment, a lot better then mine, but most of them have also more frames stacked then I have normally. I also live near a small city so from my home I get really rare moments of good seeing. SO I have to go to the nearby mountain about 1100-1300 m high (depends what I want to observe), where seeing is much better. But my biggest problem is the lack of time. I hope I can get close to your results 🙂 in some time. Do you mind if i contact you if I have some questions about your setup. BR Peter, Spodnje Hoce, Slovenia

    • star-watcher

      Hi Peter
      Thank you very much for your comment. I’m very happy with the 70D(a). But I don’t know the 40Da… What I can say is, the 100D at ISO1600 has almost the same noise like the 70D at ISO2000. I use the 70Da always at ISO1600. Read more here about ISO values for Canon DSLRs for astrophotography:
      Surely, you can contact me if you have questions! We have almost the same setup 😉
      ClearSky, Karol

  2. Saif

    Hi Karol,

    Do you shoot Galaxy with CLS filter on ? The reason I asked, I shot M31 other day with CLS on and it suppressed red channel significantly while blue and green channel crossed upper third of the histogram. Basically I recorded not much data from galaxy. But when I used CLS filter on Nebula (like emission nebula), worked well.

    So what do you think of using CLS with Galaxy? If you have shot Galaxy with CLS, can you tell me where do you keep the Red channel on histogram on unedited subframe. Probably posting an screenshot of histogram of an unedited sub will be helpful.


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