The planetary nebula M57 is about 2,000 light-years away in the constellation Lyra and is aligned facing us so we see the ring, which is a donut shape, in face-on orientation. The central region of gas is football-shaped (American football, not soccer) going through the donut, with the long axis perpendicular to the donut ring. NASA has a nice video of the 3D structure. 

In this HOO image taken with an L-eXtreme filter, the red channel is probably about equally from Ha (656.3 nm) and NII (654.8 and 658.3 nm) which has similar flux in M57, though some of the NII may be lost with the 7 nm bandwidth. A 3 nm bandwidth is needed to separate Ha from NII completely. The blue-green is from OIII. For those interested, spectra for many planetary nebula can be found here. Note the galaxy IC1296 is very faint in my image since I have only narrowband data.

I had hoped to properly capture the very faint outer shells, but unfortunately, those shells are much more difficult than I had anticipated, and thus, not yet at the level I wanted. Unfortunately, I had not started this project early enough in the season, M57 is too low for me to collect any more data. Note I am in Bortle 8, so even with a NB filter my sky brightness is much higher than if I were in darker skies. As it is, processing was incredibly difficult on those outer shells. The final image here is processed as three layers, the core, the outer shells, and the stars, all combined in Photoshop layers. To better match the correct colors, the green channel was adjusted to 0.1 R + 0.9 G using Photoshop channel mixer, somewhat less than the 0.2 R than suggested by Alberto Ibañez, which I found too much for this image, washing out the R. The outer shells are mostly Halpha, but in all my processing I ended up with bluish-green areas in the outer shells, which doesn't appear in many images. However, others have also seen this signal, as in a recent image by @Wei-Hao Wang. Thus, this appears to be a real OIII signal where the Halpha/NII is weaker than in other parts of the outer shell. I'm looking forward to adding more data next year, as there is a lot more detail to be brought out here.