I chatted once with Don Goldman about 3nm filters. He recommended 3nm for O111 and 5nm for Ha was fine as it allowed nitrogen (is it N3??) to go through.
But I think it was assumed we were imaging from dark sites.
O111 seems the real winner though in 3nm from the images I have seen.
With 5nm I don't really like to image with the full moon or with the object too close to a 1/2 or more moon. So there is that. The downside is it will require longer exposure time to compensate.
Greg.
|