This filter set is a set of narrowband filters.

The S, H and O in the name refer to the elements in space whose emission wavelengths are being captured.

S is for sulphur, which emits light at 671.6nm and 673.1nm from its singly ionised form, although the emission at 673.1nm is significantly stronger.

H is for hydrogen, specifically hydrogen-alpha which refers to one of the emission lines of the Balmer series, and the emission wavelength for this is 656.3nm.

O is for oxygen, which in its doubly ionised form emits at 495.9nm and 500.7nm, with the 500.7nm wavelength being the stronger of the two.

In all cases, there are additional wavelengths being emitted but they are either too weak to be of interest or are outside the wavelength range that can be detected by camera sensors. The emission of photons is the result of electrons associated with the atomic nuclei dropping from high energy states to lower energy states, with the energy difference precisely matching the energy of the photon emitted. Different energy means different wavelengths. The initial excitation of the electrons to higher energy states is caused by the absorption of energy from radiation emitted by nearby stars.

The transmission curves of each filter in the set are shown below.

Further details on the Antlia website are available for the SII, Ha and OIII filters.