The ZWO SII 7nm narrowband filter passes light at 672nm wavelength with a bandpass of 7nm which is designed for nebula observation and imaging. It is suitable for visual observation on most emission nebulae, planetary nebulae and supernova remnants, use it with H-alpha and OIII narrowband filters (SHO Set) for tricolor CCD astrophotography or use it with a H-alpha filter to create bicolor images of nebulosities.
Narrowband filters are used to create high contrast deep sky images of certain objects, mainly emission and diffuse nebulae (i.e. Veil Nebula, M42 Orion Nebula, North America Nebula, Horsehead Nebula) or planetary nebulae (i.e. M27 Dumbbell nebula, M57 Ring Nebula, Helix Nebula), just to mention few of well known nebulosities. Narroband filters are sometimes used instead of LRGB filter sets and sometimes in combination with them...However, if you don't yet want to commit to full narrowband H-S-O imaging, you might just buy them one-by-one and still be able to use them, i.e. a SII filter could be used together with a H-alpha for bicolor astrophotography for certain deep sky objects, usually nebulosities...
Some amateur astronomers would use narrowband filters when the Moon is out or if they live in heavily light polluted areas as these filters would practically eliminate the effects of light pollution as a side effect. By applying longer exposure time you will increase the brightness of the nebulosity whilst stars will still apear much fainter (thus smaller and sharper) than if they were imaged with LRGB filters. The sky's background will also stay darker hence contrast will be increased.
We would recommend to use narrowband filters with fast imaging telescopes with f/8 and faster focal ratio.
Specifications: ZWO SII 7nm Narrowband Filters, Mark II
Fine-optically polished to ensure accurate 1/4 wavefront over both surfaces
FWHM_¦_7 “Ï 0.5nm
Thickness of glass: 1.9mm “Ï 0.03mm
Total Thickness: 9mm = 5.5mm + 3.5mm (thread)
Optical Length: 5.5mm
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