Clip-on filter for Canon EOS R mirrorless APS-C cameras
The Astronomik SII filter is ideal for photographing nebulae with sulphur emissions from both light-polluted and dark observation areas. It significantly increases the contrast between objects emitting light at 671.7 nm and 673 nm (SII lines) and the sky background. The Astronomik sii filter blocks all emission lines from high- and low-pressure sodium and mercury vapour lamps, the maxima of typical LED lights, most lines of natural airglow and distracting moonlight. For particularly high-contrast results, the Astronomik sii filter is optimised so that H-alpha light is not transmitted.
The filter effectively blocks all unwanted light with wavelengths outside the range of 671.7 nm and 673 nm, from ultraviolet (UV) to infrared (IR).
Difference between Astronomik 12nm, 6nm and 4nm Filters
The choice between 12nm, 6nm and 4nm half-width depends on your imaging conditions and your camera type. There is no universally ‘best’ option – each half-width serves a specific purpose.
The 12nm Astronomik narrow-band emission line filters are optimised for use with system cameras featuring CMOS sensors. They are also a good choice for CCD cameras with normal or high dark current. The 12nm filters are also the preferred choice for cameras with an integrated tracking sensor, as they show more guide stars compared to filters with a 6nm or 4nm half-width.
The 12nm filters offer the most affordable entry point into imaging with narrow-band emission line filters. Generally, the background signal in images taken on the outskirts of a town or in a location with a dark sky is limited by the sensor’s dark current rather than by light pollution. Further suppression of the sky background by reducing the half-width therefore does not reveal any additional details of the object.
The Astronomik MFR 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.
12nm MFR-coated filters can be used in all instruments with aperture ratios from f/3 to f/15 without any visible loss of performance.
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.
