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Astronomik CLS Visual XT WIDE FIELD Clip-Filter for Canon EOS APS-C Cameras

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Astronomik CLS Deep Sky & Light Pollution XT Clip Filter for Visual Observations & WIDE FIELD B&W and CCD Photography
Mounted filter in EOS Clip Cell

The new Astronomik XT filters are designed to give you widefield-images with beautifull crisp and sharp stars right to the edge of the field.
Our Astronomik Clip filters are a popular and very well known tool among astrophotographers in the whole world.  Sadly image quality was limited when using them with very short focal lengths to take widefield images: Even if the normal Astronomik filters are made of 1mm thick glas only, some wideangle lenses showed aberations in the edge of the field of view when used with Clip-filters.
The new Astronomik XT filters are coated on an ultra-thin substrate with a thickness of 0.3mm only! Due to that the residual aberations are minimized and stars are crisp and sharp right into the corner of the image.

Comparision image, taken with a Canon 700D and a Sigma 10-20 mm F4,0-5,6 EX DC Wideangle lens at 10mm. Compare star sizes/figures with a conventional 1mm Astronomik filter and the 0.3mm Astronomik XT filter!

1mm Clip-Filter

Image 1: Taken with an Astronomik CLS Filter with the normal thickness of 1mm

 XT Clip Filter

Image 2: Taken with an Astronomik CLS Filter XT Filter with a thickness of only 0.33mm

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.

Astronomik has re-designed all of their photographic filters. Since the end of 2008 they are shipping their new "Halo-Free" filters.

For full compatibility list please visit the manufacturer's website. Click here!

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.


Main use

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.


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

Technical Data

  • 97% transmission at 656nm (H alpha)
  • 92% transmission at 486nm (H-beta)
  • 92% transmission at 496nm (OIII)
  • 92% transmission at 501nm (OIII)
  • pass from 450 to 540nm and beyond 650nm
  • Parfocal with other Astronomik filters
  • Glass thickness: 1mm
  • 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




How to read the above chart?

    * The horizontal axis is the Wavelength in Nanometers (nm). 400nm is deep blue, at 520nm the human eye senses green and at 600nm red. At 656nm is the famous "H-Alpha" emission line of hydrogen.
    * The transmission in % is plotted on the vertical axis.
    * The red line shows the transmission of the filter.
    * Visual filters: The grey line filled with grey  in the background shows the relative sensitivity of the human eye at night. The maximum is at ~510nm and drops to longer and shorter wavelengths. You can easily see, that you can´t see anything of the H-alpha line at night (even if you can during daylight!) The sensitivity of the eye at 656nm is 0% at night!
    * Photographic filters: The grey line in the background shows the sensitivity of a typical CCD sensor.
    * The most important emission lines from nebulas are shown in green. The most important lines are from ionized Hydrogen (H-alpha and H-beta) and double ionized oyxgen (OIII) .
    * The most important artifical emission lines are shown in orange. The artifical light pollution is dominated by mercury (Hg) and sodium (Na), which are used in nearly all streetlights.


The major emission lines of artifical light pollution:

| Hg 435,8nm | Hg 546,1nm | Hg 577,0nm |
Hg 578,1nm | | Na 589,0nm | Na 589,6nm |
Na 615,4nm | Na 616,1nm |

The major emission lines of nebulas:

H-β 486,1nm | OIII 495,9nm | OIII 500,7nm |
H-α 656,3nm


Please note, image is for demonstration purposes only. Shows the CLS version of the same EOS Clip-type of filters. Digital camera is not included.

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