I was looking for transmission spectra for the ANTLIA 3 nm 2” SHO filters (standard version, non-highspeed). I did not find any spectra on the antlia website. However, for the 50 mm ummounted version I found this:
📷 image.png
Sources:
http://www.antliafilter.com/pd.jsp?fromColId=137&id=96#_pp=137_607
http://www.antliafilter.com/pd.jsp?fromColId=137&id=61#_pp=137_607
http://www.antliafilter.com/pd.jsp?fromColId=137&id=91#_pp=137_607
So it seems for OIII and Ha the transmission window is exactly centered around the corresponding emission line. This would mean that approximately half of the transmission window is not used because angles of incidence larger than zero lead to a blue shift of the transmission window. I thought that narrowband filters (even non-highspeed versions) are usually slightly red-shifted towards the emission line to compensate for the blue shift of larger angles of incidence.
This seems really odd to me. And it is really strange that they only show the spectra for this particular filter size. I am wondering whether these spectra are actually correct. I have the following questions:
Does anyone know whether the transmission windows are actually dead center on the emission lines? Does anyone have spectra for the actual mounted ANTLIA 3 nm 2” SHO filters (normal version)?
Would there be any reason for this filter design?
Might it be that these spectra are already “effective spetra” taking into account the angular distribution of typical telescopes (e.g. f/5)? So the do not show the spectra for a collimated beam?
