I have just started giving narrowband a try. My first target was the W. Veil with Ha and the next night, Oiii. The first set of exposures I use unity gain, -10C and 240 sec. subs x 50. The next night with Oiii, I noticed that it took a little more exposure to focus then with the first set of subs, I noticed that even stretched the veil was just barely visible. So, I increased the exposure time to get a decent signal. In retrospect, I think that was a mistake. I use APP and in the past trying to process an image with using subs with different exposure times hasn't worked out well. When using different narrow band filters, how do you adjust the exposure between the different filters. I would guess by changing the gain and using the histogram???