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Astronomik CLS Light Pollution Filter - Canon EOS Full Frame Clip

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Astronomik CLS Light Pollution Filter - Canon EOS Full Frame Clip

A CLS Light Pollution Filter in a Full Frame XL Clip for Canon EOS cameras by Astronomik:

The Astronomik CLS is a budget filter for visual observation, Black & White photography and CCD photographs of nebulae, galaxies and star clusters with astronomical instruments of any size.

The Astronomik CLS blocks the light of the spectral lines of mercury and sodium-vapor lamps and lets the largest part of the visible light and H-alpha emissions pass. All the important emission lines, as well as the spectral region that the very well dark adapted eye can see, can pass through the filter.

The filters are optimized for use with aperture ratios from 1:3 to 1:15. Transmission losses and chromatic distortions, which are problems with other filters, only appear with Astronomik filters when extremely bright aperture ratios of 1:2 and more are used. The CLS filter is suitable for use with telescopes of all aperture sizes and even works well with binoculars.

The Astronomik CLS Light Pollution Filter is good for use under both dark and urban skies for reducing light pollution made by mercury-vapor lamps. For film photography and modified DSLR use, the CLS filter gives good performance and near perfect color balance. While this filter does perform well with webcam and video equipment under light polluted skies, it is not suitable for planetary use.



  • Visual observation (dark skies): Good, to reduce light pollution by mercury-vapor lamps (streetlight)
  • Visual observation (urban skies): Good, an UHC-E or UHC filter is more suitable
  • Film photography: Very good, color balance is near perfect CCD photography: Good, when used with an additional IR-block-filter
  • DSLR photography (original): Good, colour balance shifted but contrast enhanced
  • DSLR photography (astro modified): Very good, color balance is near perfect
  • DSLR photography (MC modified): Good, when used with an additional IR-block-filter
  • Webcam / Video (Planets): Unsuitable
  • Webcam / Video (Deep Sky): Very good, if light pollution is a big problem


About the Astronomik XL Clip-Filter System: The patented Astronomik Clip-Filter System for Canon full-frame cameras is black anodized aluminum and laser-cut on state-of-the-art modern machines. It can be inserted within seconds directly into any full-frame (5D and 6D, for example) EOS camera body. There are no changes necessary and all lens functions (focus, screen, image stabilization) remain functional! If you have a EOS Rebel, or other Canon APS-C sized camera body, you should purchase the standard-sized Astronomik CLS EOS Clip filter instead.

[Exception: Does Not work with the Canon 5D Mark IV].

Almost all Canon system lenses (with the exception of the EF-S series) and all M42 and T2 lens adapters, can be used with the Astronomik Clip-Filter System. The Clip-Filter System also acts as an outstanding dust shield, which prevents the possibility of dust settling on the sensor during long time exposure (The MC-Clear filter does not have a filter effect and only acts as a dust shield.)

Astronomik CLS Light Pollution Filter - Canon EOS Clip Features:

  • 92-percent transmission at 486 nm (H-beta)
  • 92-percent transmission at 496 nm (OIII)
  • 92-percent transmission at 501 nm (OIII)
  • 97-percent transmission at 656 nm (H-alpha)
  • Pass from 450 to 540 nm and beyond 650 nm
  • Parfocal with other Astronomik filters
  • Glass thickness: 1 mm
  • Completely resistant against high humidity, scratches and aging effects
  • Diffraction limited, the filter will not reduce the optical performance of your telescope!
  • Astronomik filters are delivered in a high-quality, long lasting, filter box


OPT Product Number: AK-CLS-EOSXL


Please Note: Clip-Filters:

Clip-in EOS XL filters are for these Canon Full-Format Cameras:  5D Mark II, 5D Mark III, and 6D.  (5D Mark I will work without LiveView only) 

The Astronomik XL Clip filters will not work with the Canon 6D Mark II, 5DS, 5DSR, the 5D Mk IV camera bodies, and will only work without LiveView in the Canon 5D Mk I.



Filter TypeCLS
Free ShippingYes
Warranty10 Year Warranty

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Not for all full frame cameras, beware!

Despite all the excellent reviews, this doesn't work with the Canon 5Ds. Before buying I saw nothing that indicated this. Research is only as good as the data out there.

United States

A good recommendation

This filter is easy to use, and suits my needs nicely. I’m not using it for astrophotography, but rather another project. I told one of your sales reps about the project, and he recommended this filter based on my description. I’m happy with the results.

Steven B.
United States

Works as advertised

Substantial improvement reducing light pollution in my Astro photos

Andrew W.
United States

Fast ship and great service

I ordered the filter on a Sunday. Much to my surprise, the shipment took place early Monday morning. Thanks OPT!


Great for LP regions, with a caveat

I originally started astrophotography with my Canon EOS 7D and Canon EF 600mm f/4 L II lens. The combo was a great start, the fast aperture worked well with the 7D to lift the red channel above the noise floor. I started right off the bad with the Astronomik CLS for EOS APS-C cameras, and the experience was wonderful. I recently added a 5D III to my collection of DSLRs, and decided to stick with the CLS for an LP filter. In terms of function, the Astronomik CLS-XL for FF Canon DSLRs works the same as the one or APS-C. Clipping the filter in is a little more difficult, as it requires locking the mirror up, and it stays up until you remove the filter. There is one caveat to using this particular filter that is rather frustrating. The way it is designed, the filter is clamped into a small metal holding frame in such a way that the holding frame actually adds a significant amount of vignetting at the top and bottom of the frame. I leave the filter in when I take my flats, however even when doing that, the flats are insufficient to fully combat the vignetting problem. This is rather disappointing, as it effectively forces you to lose some of the frame area benefit of the 5D III (or, for that matter, any Canon FF DSLR). I always have to crop the top and bottom, and to some degree the left and right edges. I would recommend to Astronomik that they redesign the FF Canon EOS CLS clip-in filter to eliminate the vignetting. Find a way to attach the filter to the holding frame in such a way that it does not require the frame to actually wrap around into the light path. I intend to continue using the filter, as without, LP causes my background sky to increase at much too fast a rate, and my exposure times are severely limited (which poses a real problem for exposing the red channel deeply enough to separate it from the left edge of the histogram and lift it above the noise floor.) I am happy to be able to use an effective LP filter with my DSLR. It definitely blocks out a LOT of LP, and despite the rumors, calibrating nebula and background sky color in post is pretty easy. Star color suffers very slightly (much like using an Ha nd OIII filter), however that hasn't been a major issue for me when it comes to my nebula photography. Frankly, though, I am a bit bummed that this filter cost $200 when it has such a severe vignetting issue. I truly believe Astronomik should address the issue and release a revamped version of the product, especially with the Canon EOS 6D becoming a popular astro-modded full-frame model!