Astronomik CLS Visual Deep Sky & Light Pollution Filter 2 in
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
- 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
- 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 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!
- 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).