Baader's New f/2 Highspeed Narrowband Filters and Filtersets
(1¼" H-alpha / O-III / S-II) are designed especially for the delicate requirements of extremely fast astrograph optics, such as Hyperstar, RASA, and ultra-fast instruments from TEC/AP/ASA/etc. Conventional narrowband filters cause a heavy loss in transmission due to the strong CWL-shift. In extreme cases the CWL even shifts out of the FWHM (CWL= Center-wavelength / 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 the effective use of extremely fast optics for high contrast imaging of emission nebulae. Using these filters between f/1,8 and f/3,5 shows a dramatic improvement compared to any regular set of narrowband-filters.