The SII line at 672nm, close to the one of H-alpha, is emitted from various planetary and extended nebulae. This line is particularly useful for astronomical photography as it can be studied with special filters that isolate it from the rest of the electromagnetic spectrum. This is precisely the action of our SII CCD 12nm filter.
In the same way of H-alpha filter, this filter dramatically increases the contrast of the image as the background sky turns black and make appear areas and details of the nebulae that are not visible without a filter. The filter also decreases the size of the stars highlighting even more nebulae. The SII CCD 12nm filter can be used together with our filter H-alpha and O-III CCD 12nm to "reconstruct" color images of deep sky objects that emit light in specific wavelengths, such as gas nebulae. In fact you can take a picture for each different filter and use a special processing software (indicating that each filter corresponds to one of the R, G and B channels) to get the color image. This technique is very useful to use monochrome CCD cameras for color images even from places with strong light pollution.
This filter is also perfect for use with achromatic or semi-apochromatic refractors that, because of the chromatic aberration, are not usually indicated for the long-exposure photography. But, using this filter the deep-sky photography becomes not only possible but also provides excellent results since the narrow bandwidth practically cancels the effect of chromatic aberration.
Visual use: because of the very narrow bandwidth, the light that reaches the eye is greatly reduced so this filter is not suitable for visual use.
The filters are available in two diameters: 31.8mm and 50.8mm. These standards are commonly used by telescopes and their accessories. For example, depending on their function, they can be used with a CCD ora A DSLR camera (using appropriate photo adapters), but also screwed to optical accessories such as eyepieces or diagonals.
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