Baader 1.25" f/2 Highspeed O-III Filter w/ LPFCThe 1.25-Inch f/2 Highspeed O-III Filter w/ LPFC by Baader Planetarium:
Baader's new f/2 Highspeed Narrowband filters are made specifically for the sensitive requirements of exceptionally fast astrograph optics, such as HyperStar, RASA, and extremely fast instruments from TEC, AP, ASA, etc. Ordinary narrowband filters generate a heavy loss in transmission because of the strong CWL (center-wavelength) shift. In severe circumstances, the CWL even shifts out of the FWHM (full width half maximum).
As a result, this filter has a CWL-pre-shift which flawlessly matches f/2 to f/3. Furthermore, the FWHM is enhanced. Despite the typical line broadening with such fast optical trains, this filter is still able to produce peak contrast. This filter permits the effective use of tremendously fast optics for maximum contrast imaging of emission nebulae for the first time. Compared with regular narrowband filters, using this high-speed h-alpha filter between f/1.8 and f/3.5 will exhibit drastic improvement.
OPT Product Number: BA-FOIIIHS-1