Subject: Crescents using four filters
three of them in the red part of the spectrum: [SII], Ha, [NII] and one [OIII]
the first image is a pseudo-true color image made by reassembling the various lines into their proper order and by synthesizing the Hbeta line from the Halpha
The second is a classic wavelength-ordered palette using Sulfur, Hydrogen and Oxygen
the last is Nitrogen, Hydrogen and Oxygen in their wavelength order
http://www.narrowbandimaging.com/ngc...2hao3_page.htm
