Glossary | Telescope accessories | General | Series | SII 6nm CCD
The SII 6nm CCD series of filters are ideally suited to the photography of SII emission line objects from light-polluted areas as well as from dark sky locations. The contrast between objects that emit light of the sulphur line at 672nm and the background sky is greatly enhanced.
Transmission and full width at half maximum
The full width at half maximum of 6nm is perfectly adapted to the use of CCD and CMOS sensors with particularly low dark current. The 6nm filters are the best choice if you are observing from a location with extreme light pollution or generally whenever weak objects are to be photographed in regions of the sky with many stars.
What does CCD mean?
CCD filters also feature an integrated IR block. This is particularly important for photography, since although the camera sensors are sensitive to this long-wave spectral range, the upstream optical instruments (telescopes, etc.) cause imaging errors in the infrared range.
Such optical errors do not play a role for purely visual observation, since the human eye anyway cannot perceive them. If you want to specifically photograph in the IR range, you should not use a CCD filter.