Astronomik XT filters for wide-angle optics: With these filters, you can achieve 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 streaks.
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 photographing hydrogen nebulae from areas with artificial light pollution, but also from places with dark skies. The contrasts between objects that glow in H-alpha light and the sky background are greatly enhanced.
The H-alpha filter increases the contrast between hydrogen nebulae and the sky background. Due to the narrow half-width and high transmission in the H-alpha line, the filter achieves a greater contrast increase than broadband filters. The half-width of 12nm is optimally matched to the use of common CCD and CMOS sensors. The half-width makes it possible to use fast optics. In addition, the filter has a transmission of almost 100%, which cannot be achieved with narrower filters.
Even in large cities, images taken with cooled CCD cameras are usually limited by dark current. Therefore, further suppression of the sky background by lower half-widths does not reveal more details in the object. Compared to very narrow-band filters, the H-alpha 12nm filter has the advantage that you can usually find guide stars for almost all cameras with built-in tracking sensors. The useful range extends over an aperture ratio of 1:2.8 to 1:15 for lenses and telescopes of all diameters.
Mode of operation
The filter completely blocks the emission lines of low- and high-pressure lamps (mercury (Hg) and sodium (Na)) and the lines of the airglow. The filter increases the contrast between objects that glow in the H-alpha emission line and the sky background.
Tips and further usage information
Together with the OIII CCD and SII CCD filters, you can also take three-colour images of emission line objects from locations with very strong light pollution, as is well known from images taken with the Hubble Space Telescope. The Astronomik H-alpha filters are not suitable for solar observation!
Suitability of the filter
- Visual observation (country): Not suitable
- Visual observation (city): Not suitable
- Conventional film: Neutral, but very long exposure times
- CCD astrophotography: Very good, extreme contrast gain with H II emission nebulae
- DSLR astrophotography (unmodified): Good, but significantly lower sensitivity in H-alpha than with modified cameras
- DSLR astrophotography (astronomically modified): Very good, extreme contrast gain with H II emission nebulae
- DSLR astrophotography (converted with MC clear glass): Very good, extreme contrast gain with H II emission nebulae
- Webcam / video (Planets): Not suitable
- Webcam / video (deep sky): Good, good contrast gain with bright objects
Technical data for the filter
- Transmission of over 97% at the H-alpha line (656 nm)
- HWB 12 nm
- Complete blocking of all interfering wavelength ranges down to infrared
- Homofocalwith all other Astronomik filters
- Filter thickness: 1 mm
- Not sensitive to moisture, does not age, scratch-resistant
- Fine-optically polished carrier material
- The filter is supplied in a durable case
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!
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.
