Baader F/2 Highspeed-Filter S-II 1.25
New f/2 Highspeed Narrowband Filters and Filtersets.
Available in 1 ¼", 2", H-alpha / O III and S II are designed especially for the delicate requirements of extremely fast astrograph optics, in particular Hyperstar and Celestron's New RASA.
Conventional narrowband filters cause a heavy loss in transmission due to the strong CWL shift (CWL= Center wavelength).
In extreme cases the CWL even does shift out of the FWHM (FWHM= full width half maximum).
Therefore these filters have a CWL preshift which matches f/2 to f/3 perfectly.
Also the FWHM is optimized. In spite of the typical line broadening with such fast optical trains they are able to deliver maximum contrast. For the first time these filters allow to use fast optics really effectively with high contrast emission nebulae imaging. Using these filters between f/1,8 and f/3,5 shows a dramatic improvement compared to any regular set of narrowband-filters.