Astronomic filter S-II with a half width of 6 nm in the frame 1.25 "/ 31.7 mm.
The SII-CCD filter is an appropriate filter for photographing the sulfur emission line both from areas contaminated with light and under dark, rural skies. Increases the contrast between the glowing object 672 nm and the background.
The combination of a narrow bandwidth of 6 nm and a high transmission of typically 96%, the filter provides an extraordinary jump of contrast, since all unwanted light from other than the 656 nm band is blocked, from UV to IR. Thanks to this, a very dark background is achieved.
FWHM (half-width) equal to 6 nm guarantees the best results with CCD and CMOS matrices with very low dark currents. 6 nm is the right choice for people watching from areas that are very polluted with light and for people photographing weak objects in those areas of the sky where there are a lot of stars (mainly in the Milky Way). • blocks all unwanted light - artificial pollution with light, natural light of the atmosphere, moonlight; in particular, it blocks sodium and mercury lines • using H-alpha, O-III and S-II filters, you can get a color photo consisting of three emission lines (HSO) in whole, even when shooting under extremely bright skies, eg in the center of a large city
• users photographing a SLR camera or CCD camera with a high dark current should choose a filter with a FWHM of 12 nm or more.
• a filter designed for shooting with devices with a light to f / 4; with a larger light (eg with bright lenses f / 2), the filter will not work optimally (reflections). • the filter is not intended for observing the Sun.
• guaranteed transmission above 90% for the H-alpha line (672 nm)
• typical transmission for S-II line is 96%
• half line width (FWHM): 6 nm
• blocks the remaining wavelengths from UV to IR
• parchocal with other Astronomic filters
• MRF layers
• thickness: 1 mm
• resistant to moisture, scratch, does not age, without residual material stress 
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