OPTOLONG SII FILTERS
The Optolong SII narrow-band filter boosts the contrast of emission nebulae and supernova remnants for professional results, even under a bright sky affected by light pollution. This filter is used in combination with the H-Alpha and SII filter to combine a narrowband colour image.
The 6.5nm band pass is only 2% of the entire visible spectrum, increasing the signal to noise ratio and delivering high contrast images and extremely dark backgrounds.
The maximum transmission of the Oxygen III line (500.7 nm) is above 80% and the transmission off band is only 0.1%. This is a value often undisclosed by other filter producers and it is critical to darken the sky background and minimise the halos around the stars.
The filter cuts off the ultraviolet and infrared light so there is no need to use the IR-cut filter.
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