I started this photo 4 years ago, the winter here has very few nights with affordable seeing and is not always suitable for long focal. In any case, this year I was able to add the HA layer to my rendition of M51 galaxy, with a 5nm filter. That has significantly changed the color rendering of the whole previous version.
This is the result:
http://www.starkeeper.it/M51HA.htm
I hope you'll find it interesting.
All the best,
Leo