Baader Planetarium 36mm Round 3.5nm Ultra-Narrowband H-alpha CCD Imaging Filter

• Precision grade enforced H-alpha filter for f/10 to f/3.5 optical systems• Opens up the extremely narrow 3.5nm H-alpha world• This enforced contrast results in even fainter stars, providing more signal of faintest nebulae detail• Manufacturing such ultra-narrow filter does require extreme coating homogeneity and very high CWL precision, which these filters are designed for. CWL= Center-wavelength / FWHM= full width half maximum