This filter is suitable for photography and observation from areas with artificial light pollution. It enhances the contrast of all deep sky objects.
The CLS filter increases the contrast between astronomical objects and the sky background. Due to the large half-width, a correspondingly large amount of light is transmitted, so stars are only slightly attenuated. The CLS filter is designed to block as much stray light as possible while still allowing as much light as possible to pass through to the objects. The useful range of application extends to visual observation with an aperture ratio of 1:2 to 1:15 for telescopes with an aperture of 2" (50 mm) or more and for CCD, DSLR and chemical black-and-white photography through lenses and telescopes of all diameters.
Mode of action
The filter completely blocks the emission lines of low- and high-pressure lamps (mercury (Hg) and sodium (Na)) and the lines of airglow. All important emission lines of astronomical objects and the spectral range in which the eye has maximum sensitivity at night are transmitted.
Tips and further usage information
In the EOS Clip Filter version, the filter allows photography with DSLR cameras even in extreme light pollution without damaging the colour balance.
Alternatives
If no built-in IR blocking filter is available for electronic photography, a CLS CCD filter is required.
Suitability of the filter
- Visual observation (country): Good, with light pollution from mercury vapour lamps
- Visual observation (city): Good, a UHC-E or UHC filter is more suitable
- Conventional film: Very good, white balance is very good
- CCD astrophotography: Good, additional IR blocker required
- DSLR astrophotography (unmodified): Good, colour shift but improved contrast
- DSLR astrophotography (astromodified): Very good, white balance is very good
- DSLR astrophotography (modified with MC clear glass): Good, additional IR blocker required
- Webcam / video (Planets): Not suitable
- Webcam / video (deep sky): Very good if light pollution is a major problem
Technical data for the filter
- 92% transmission at 486 nm (H-beta)
- 92% transmission at 496 nm (OIII)
- 92% transmission at 501 nm (OIII)
- 97% transmission at 656 nm (H alpha)
- Passband 450 nm to 540 nm and greater than 650 nm
- Homofocal with all other Astronomik filters
- Filter thickness: 1 mm
- Not sensitive to moisture, does not age, scratch-resistant
- Fine-optical polished carrier material
- The filter is supplied in durable packaging
