The Astronomik h-alpha filter is ideal for photographing HII regions from both light-polluted and dark observation sites.
The Astronomik h-alpha filter significantly increases the contrast between objects emitting light at 656 nm (H-alpha line) and the sky background, thus enabling long exposure times for deep and high-contrast images.
The filter blocks the emission lines from high- and low-pressure sodium (Na) and mercury (Hg) vapour lamps, the peaks of typical LED lights, most lines of the natural airglow, and the majority of the interfering moonlight almost completely.
The Astronomik h-alpha filter effectively blocks all unwanted light at wavelengths other than 656 nm, from ultraviolet (UV) to infrared (IR).
The Astronomik MaxFR Coating
Both the Astronomik MFR and MaxFR coatings offer extremely high contrast, minimal stray light, no halos and razor-sharp stars. Furthermore, they provide the best possible blocking across the entire spectral range from UV to IR.
The MaxFR coating ensures that Astronomik narrow-band emission line filters can be used with extremely fast optical systems such as the Celestron RASA and the Takahashi Epsilon Astrograph. Unlike filters from other manufacturers, which often offer special “high-speed” versions, Astronomik’s MaxFR filters retain their transmission characteristics even in standard optical systems that are less light-sensitive. Using a MaxFR filter with a standard optical system has no disadvantages whatsoever and saves you a lot of money on multiple filter sets.
For 6nm filters with MaxFR coating, this means unrestricted usability from f/2.2 to f/6 and approximately 90% of maximum transmission at f/2.
Difference between Astronomik 12nm, 6nm and 4nm Filters
The choice between 12nm, 6nm and 4nm half-width depends on your imaging conditions and camera type. There is no universally ‘best’ option – each half-width serves a specific purpose.
The 6nm Astronomik narrow-band emission line filters are usually the best choice for astrophotography. They are ideal for imaging faint objects in star-rich regions of the Milky Way, as they typically halve the number of stars in the image compared to 12nm filters, thereby significantly simplifying image processing.
The 6nm narrow-band emission line filters are particularly the first choice if you are using a CMOS astro camera or a modern system camera with very low dark current, or if you are conducting observations from a location with heavy light pollution. Thanks to their excellent suppression of the sky background, you can use long exposure times. The 6nm filters ensure a dark background and excellent rendering of details in faint nebulae.
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.
Clip-on filter for Canon EOS R mirrorless APS-C cameras
