Manufacturing such ultra-narrow filter does require extreme coating homogeneity and very high CWL precision, which these filters are designed for. Note: In general this DeepSky enforced H-alpha Filter is not suitable for solar observation. The Halfbandwidth of 3,5nm equals 35 Ångstroem, high-quality H-alpha solar filter from SolarSpectrum start at 0.8 Ångstroem.