« on: August 06, 2014, 01:11:46 AM »
Ok, I might be over simplifying this in my head, so please correct me if my line of thinking is off here....
Since the flash head zoom correlates to the focal length of the lens, at least in TTL, to find the appropriate flash zoom to fill a modifier, place your lens where the flash head would be in the modifier, if possible i.e. umbrella or mounted on the back of a softbox, and use the FL needed to just see the outer edges of the modifier. Then, the ISO and flash power settings would be adjusted for achieving the desired exposure. That way, the flash zoom for a particular modifier would be a consistent value. Again, let me know if this line of thinking is off the mark.