Baader f/2 S-II High-Speed Filter 31mm 2459383
For use in fast optics such as Celestron RASA and Starizona Hyperstar astrographs
Suited for astrographs between f/1.8 to f/3.5
Available in 1.25", 2", 31mm, 50.4mm round and 50x50mm square sizes
These Baader S-II High-speed f/2 narrowband filters are for use in fast optical systems such as Celestron's Rowe-Ackermann Schmidt Astrograph (RASA) and Starizona's Hyperstar systems. The use of conventional narrowband filters cause a heavy loss in transmission due to the strong centre wavelength (CWL) shift. In extreme (very fast) cases the CWL shifts out of the filter's full width half maximum (FWHM) transmission. Therefore these filters have a CWL-preshift which matches f/2 to f/3 optics perfectly.
In spite of the typical line broadening with such fast optical trains these filters 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.