this is done using Ha, [OIII] and the 468nm Helium II line
Helium II is a very high energy line and is only found around the hottest of the central stars....
http://www.narrowbandimaging.com/ngc...o3he2_page.htm
shot with an AP180EDT f/9 and Microline ML4022 camera and the world's best emission line filters: Custom Scientific
Because I wanted to start and finish this in a single outing, I binned it 2x2