For an astrophotographer like me, who lives in a city, and can't go to dark sites as often as wanted, Narrow band filter is the only secret to get great images from my backyard.
Since I upgraded to my F2.8 Epsilon 180, it always bothers me that maybe I should try out those narrowband filters made for big focal ratio telescopes. Plus, when processing my recent shots on the North America nebula, the ugly halo of a magnitude 5 star really bothered me. So last week, I pulled the trigger and get a new set of Baader Planetarium F/2 Highspeed narrowband filters...
