Baader Ultra-Narrowband 4.5nm S II CCD-Filter Ø 31 mm [BA-FSIINU-RD31]

Baader: Baader's New Ultra Narrowband Enforced Filters  These three sizes of Ultra-Narrowband filters upen up the extremely narrow H-alpha, O-III, and S-II world.  This enforced contrast provides more signal of the faintest nebula detail.  Manufacturing such ultra-narrow filters requires extreme coating homogeneity and very high Center Wavelenth Precision, which these filters have been designed for.  Designed for use on optical systems from f/10 to f/3.5.
Now available in all popular sizes; 1.25"Mounted, 2" Mounted, 31mm Round, 36mm Round, 50.4mm Round, 50x50 Square, and 65x65mm Square.
 
NOTE:  In general, the H-alpha ultra narrowband  filter is not suitable for solar observation.  The half-bandwidth of 3.5nm equals 35 angstroms, much wider than needed for high quality solar observation (sub-angstrom).  Never use this filter for visual observation of the sun.

- Baader 4.5nm Narrowband S-II Filters, 50x50mm Square (FSIINU-1, FSIINU-2, FSIINU-RD31, FSIINU-RD36, FSIINU-RD50, FSIINU-SQ50, FSIINU-SQ65)