This OVL high-performance CCD telescope filter only allows the H-Beta line to pass and is therefore perfect for significantly increasing the contrast of objects that radiate in this wavelength range. Eg Horsehead Nebula, Cocoon Nebula, California Nebula. It is recommended for photographing H-Beta emitting objects in CCD photography under dark skies. Scope of delivery: Filter 2″ storage box! Power supply and batteries are not included!