Astronomik CLS and packaging

Astronomik CLS


  • 1.25″ Mounted
  • 2″ Mounted (48mm threads)
  • T-thread cell (M42 thread with 0.75mm spacing)
  • SC-cell (2″ / 24TPI)
  • 31mm Unmounted
  • 36mm Unmounted
  • 50mm Unmounted
  • Canon EOS APS-C Clip-Filter
  • Canon EOS M Clip-Filter
  • Canon EOS XL Full Frame Clip-Filter
  • Canon EOS XL R Clip-Filter
  • Sony alpha Clip-Filter
  • Nikon XL Clip-Filter
  • Pentax K Clip-Filter

Spectral Transmission

Yellow line is published transmission. Color fill is my independent verification with the filter I tested. Note: I used a Quartz Tungsten-Halogen bulb which is broad spectrum, but does not have good throughput in the blues hence I only vouch for the accuracy of my independent verification from 500-900nm.

Physical Characteristics of 2″ filter

  • Filter mount thickness: above threads: 4.4mm; including threads: 6.84mm
  • 48mm threads
  • Minimal knurling only on top
  • Highly reflective interference filter

Real world tests

Bortle 4, Canon 5D mk iii (stock), AT60ED at f/6, ISO1600, 15 min integration (6*150s)
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Bortle 4, QHY168C, Cooled to -10C, AT60ED at f/6, Unity gain, 18 min integration (6*180s)
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Bortle 9, Canon 5D mk iii (stock), AT60ED at f/6, ISO1600, 10 min integration (20*30s)
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Bortle 9, QHY168C, Cooled to -10C, AT60ED at f/6, Unity gain, 16 min integration (8*120s)
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Reader Rating30 Votes
Available in many formats
Fair price
Middling star color
CLS concept outdated with move to LED streetlights
  1. I love this in so many ways. Please consider adding this pro or con to each as applicable, besides the astronomic. Seems important now. “CLS concept outdated with move to LED streetlights “

  2. Nico, as always amazing review. Thank you. How do you think the Optolong L-Pro fares with the LED street light pollution? Is that better in handling it than the CLS-CCD?

    I’m debating between a clip-in filter between Astronomik CLS-CCD and the L-Pro. I’m leaning towards the L-Pro and get a Astronomik Ha dedicated so that I can do HaRGB from the L-Pro and the Ha filters combined. What do you think?

    Thanks again. K

    1. The only filters that will do really well against LED street light pollution are Ha and SII narrowband filters. Between the CLS-CCD and the L-Pro, it’s really just a personal preference. Personally, I’d go for the L-Pro. Your plan to get an L-Pro and an Ha filter sounds good. To be clear, to achieve an HaRGB image, you would shoot one stack with just the L-Pro and one stack with just the Ha filter, and then combine these two stacks in post-processing to get the best of both (Ha for the nebular details, and L-Pro for broadband color). I think that’s what you meant, but just wanted to spell it out. Yes, it’s a good plan. Just be prepared to do many exposures with an Ha filter and a DSLR to combat the noise.

  3. Any plans to do a comparison CLS vs. CLS-CCD on an Astro-mod DSLR.

    If you’ve already done one, which gave the best results?

    1. I will add that to my list to review, but I have used both, and can tell you from experience what to expect. If your astro-mod DSLR is an ‘Ha mod’ where the UV/IR is blocked, there will be very little difference between the two filters, so you may as well buy the cheaper CLS. If your astro-mod DSLR is a ‘Full Spectrum mod’ then you will definitely want the CLS-CCD so your light pollution filter is also blocking the IR and you don’t get bloated stars from the near infrared being out-of-focus. Cheers, Nico

    1. Based on the color, I’d guess it’s likely a Neodymium filter like the Baader that I tested. Since there are limited options for clip-ins for Sony, it’s probably worth a try. I wish all companies would publish a spectral transmission graph though, because that would tell us a lot more.

  4. Nice review Nico.

    For the Canon EOS RA, is the CLS or CLS CCD clip in filter the best option would you say? I’m presuming the CCD version but I’d like to hear your thoughts.

    1. Hi Graeme,
      Between the two, I would suggest the CLS-CCD for the Ra because the Ra does not block the Near IR sufficiently which can cause red halos on bright stars. The CLS-CCD should block those wavelengths while still passing the Ha and working as a standard Light Pollution filter (blocking much of the yellow/orange part of the spectrum).
      Cheers, Nico

  5. Thanks Nico for quick reply appreciated. I know there is not much choice for in camera filter for Canon mirrorless at the moment. I did read the filters produce strong blue colour casts but I guess lightroom can fix that

  6. Have you ever tested the Astronomik CLS-CCD version of this filter?
    It is supposed to be an upgraded version to this original CLS filter.


    1. I’ve used it in the past, but haven’t had the chance to test it yet. My understanding is that it is not an upgrade to the CLS, but just a CLS that adds in IR-blocking. This is desirable for full spectrum modified DSLRs/Mirrorless OR dedicated astronomy cameras. If using a stock DSLR/Mirrorless or one that retains an IR-cut filter (Baader Mod, Ha Mod, etc.) than the CLS-CCD is not needed, and one can get the cheaper CLS. This is why they still sell both. Cheers, Nico

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Final Score