Astronomik CLS Filter
The Astronomik CLS Filter 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 Filter 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.
Suitability
- 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 (original): Good, colour balance shifted but contrast enhanced
- DSLR photography (astro modified): Very good, colour 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
The table gives you a short Overview about the suitability of our filters for various applications:
Legend ++ The filter is excellent for this application, the dramatic better image! + The filter is good for this application, the much better image! o The filter is suitable for this application, the slightly better image! - The filter is usable for this application. -- The filter is not suitable for this application.
How to Read the 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.
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Visual filters: The grey line 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 at 656nm is 0% at night!
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Photographic filters: The grey line in the background shows the sensitivity of a typical CCD sensor.
- The most important artifical emission lines are shown in orange. The artifical light pollution is dominated by see mercury (Hg) and sodium (Na), which are used in nearly all streetlights.
- 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 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
Quality Characteristics of Astronomik Filters
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Superior Substrate: Astronomik filters consist of a precision polished substrate on which the actual filter, in the form of very thin (dichroic) interference layers, is applied. Because of these high quality measures Astronomik filters will in no way reduce the performance of your optical system. And contrary to common experience with other manufacturers´ filters, with Astronomik filters stars remain fine needle points of light!
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Coating: Astronomik filters consist of up to 130 layers deposited on top of the completely transparent carrier glass. These layers work as the actual filter and as an antireflective coating.
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Durability: Astronomik filters are completely scratch resistant, and not sensitive to moisture, dew, or high humidity. With others’ filters, after a few years, you start to notice their filter is no longer up to its full capability. Not so with Astronomik filters which maintain their ‘brand new’ transmission specifications year after year. And, because of Astronomik’s extraordinarily resistant coating technology, our filters come with a 10year warranty.
Astronomik filters are highquality accessories for visual observing which will significantly expand your observing opportunities. After many years of use your Astronomik filters will be an accessory which will be ready to give you the same joy you experienced many years earlier when they were new. Now that’s an investment worth making!
