Astronomik XT filters for wide-angle optics: With these filters, you can obtain beautiful star images right into the corners of the image, even with extreme wide-angle shots.
With other Astronomik filters, the image quality in the corners of the image is limited at short focal lengths (wide angle): Although the filters consist only of a one-millimetre-thick glass plate that carries the filter layers, this plate causes aberrations with certain types of short-focal-length lenses, and the stars are pulled apart into lines.
Astronomik's XT filters are mounted on an extremely thin carrier substrate that is only 0.3 millimetres thick. This reduces "star streaks" in the corners of the image to a minimum.
The extremely thin carrier substrate of the XT filters is, of course, finely polished, stress-free and meets the highest demands of astrophotographers worldwide in every respect.
Despite this ultra-thin glass, Astronomik XT filters feature the same coating technology found in all Astronomik filters: completely scratch-resistant, moisture-resistant and non-ageing. The filter will retain 100% of its performance even after many years.
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
A bit of help with your selection:
- As a first filter, we recommend the Astronomik CLS filter. This filter suppresses artificial light pollution and natural airglow. By using this filter you get a dark-sky background and can therefore use much longer exposure times to make fainter objects visible. The filter is optimised in such a way that objects are reproduced in their natural colours. Important: the simple CLS filter has no built-in IR-blocking. Therefore you will need the CLS-CCD filter for an astro-modified camera!
- A good choice for working in locations with really heavy light pollution is the Astronomik UHC filter. The transmission curve of this filter only allows the light of the H-beta, OIII, H-alpha and SII lines to pass through. The background suppression is significantly stronger than with the CLS, however this filter works only for gas nebulae! Star clusters and galaxies are largely filtered out.
- For a more in-depth introduction to astrophotography, we recommend the OIII, H-alpha and SII emission lines filters, available with full width at half maximum of 6nm or 12nm. With these filters you can create detailed images of faint objects even from locations with extreme light pollution and a full Moon high above in the sky. Images in these narrow emission lines are not naturally coloured.
- For the owners of astro-modified cameras we offer the Astronomik OWB filter: OWB stands for "original white balance". The filter corrects the displaced colour reproduction of a converted camera so that it can also be used for normal every-day photography, without having to revise every image on the computer.
Please note: In principle, all camera lenses can be used with the Clip-Filter - i.e. Canon EF lenses or camera lenses from other third party manufacturers such as Sigma, Tamron, Tokina, Walimex etc. However, the use of clip-filters with Canon EF-S lenses is NOT possible!
