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 filters with 12nm, 6nm and 4nm half-width: The choice between 12nm, 6nm and 4nm half-width depends on your shooting conditions and camera type. There is no universal "best" option - each half-width serves a specific purpose.
The 4nm filters are the perfect choice if you are photographing from a location with extreme light pollution. They are ideal for capturing faint objects in extremely star-rich regions of the Milky Way, as they typically reduce the number of stars in the image to a third compared to the 12nm filter. The filters are also the right tool if you have a camera with very low dark current, allowing you to take very long exposures with minimal background noise.
MRF-coating: thanks to the new MFRF coating technology, it is possible to use the filter on all devices up to an aperture of f/4.
Due to the high-precision machining of the carrier material, all Astronomik filters are homofocal. The filters are plane-parallel with a wedge error that is well below all standard tolerances. Astronomik filters are diffraction-limited and ensure that the optical performance (resolution and contrast) of your telescope is not compromised. Problems with the focal point and the exact alignment of the images of the individual colour channels are thus effectively eliminated.
All Astronomik filters are ideal for modern cameras, both CMOS and CCD-based models, allowing you to capture the best possible images with your equipment. Sharpness, contrast and the absence of any reflections or halos are guaranteed. Even with bright stars in the field of view, nebulae and galaxies are imaged with the finest structures.
Every Astronomik filter undergoes strict quality control before delivery. In addition, every Astronomik narrowband emission line filter is measured with a high-end spectrophotometer from PerkinElmer to ensure that it meets the specifications. On the back of each narrowband emission line filter, you will find a label indicating the exact spectral data for that filter, including the maximum transmission and the recommended range of aperture ratios.
