Askar SII 7nm Narrowband Imaging Filter - 36mm Unmounted
Askar SII 7nm Narrowband Imaging Filter - 36mm Unmounted (glass only)
The Askar SII 7nm filter is suitable for imaging of SII emitting nebulae or some supernova remnants. The Askar SII filter has an extreme high transmission at a center wavelength of 671.6nm. The 7nm narrow bandwidth enables this astroimaging filter to block all the light pollution and other unwanted artificial lights or night glow. So the Askar SII filter is an ideal instrument for astro-imaging in heavily light-pollution hit locations and delivers enhanced contrast at darker places.
The Askar SII filter is designed to improving the contrast and details of some nebulae and supernova remnants. Though there is very little sulfur in nebulae, but the emission from the trace of S II in nebulae is rather strong. The deep-red light emitted from SII can bring out the quite delicate detail which is different from those regions that release SII light. So it works well on those nebulae emitting SII. Featuring 7nm narrow bandwidth and a greatly high transmission at a center wavelength of 671.6nm, the Askar SII filter can bring out the most amount of details of the emission nebulae, planetary nebulae and supernova remnants. Also, the out-of-band blocking ability is rated with OD4 (0.01%) with the blocking range of 200-1050nm. It delivers an excellent signal-to-noise ratio and a sharp cut-off rate to attenuate the disturbance from other wavelengths.
The narrow bandwidth and an effective cut-off rate are important indices when choosing a narrowband filter. The Askar SII filter has a narrow bandwidth of 7nm and an extreme transmission of 90% at the peak, in the meanwhile, sufficiently suppressing other off-band wavelength. That’s why we sometimes call those 7nm-bandwidth, or even a smaller bandwidth of 3nm, a line filter. So the Askar SII filter can efficiently reject all the light pollution. You can expect a terrific performance of this SII filter in artificially-brighten background sky.
The production process is strictly controlled and every single Askar SII narrowband filter is individually examined and tested to ensure that they can highly satisfy the observing interests and needs of our customers.
- Narrow 7nm bandwidth, properly designed for astrophotography both in light polluted or dark locations.
- Useful for imaging SII emitting nebulae, planetary nebulae and supernova remnants.
- High transmission of 90-95% and sharp cut-off can greatly enhance the contrast and bring out the most detailed information for those deep-sky objects.
- Designed to sharply cut off the inference of artificial light from sodium vapor or mercury vapor street lights and other unwanted disturbance like sky glow.
- The Askar SII narrowband filter is not suitable for visual observation and not designed for imaging or observing the sun or other non-SII-emitting objects.
ATTENTION! DO NOT USE THIS FILTER FOR OBSERVING THE SUN! PERMANENT EYE DAMAGE MIGHT BE THE RESULT IF YOU DO.
Images are for demonstration purcposes only. Might show a similar product or the same product, but different size.
Askar SII Narrowband (7nm) Filter Specifications
round and mounted in cell
Angle of incidence
FWHM (full width at half maximum)
CWL (central wavelength)
＞90% at 672nm
OD4(0.01%) @ 200-1050nm
black anodized matte