Hi I ordered a 720nm IR filter and I wanted to calculate how "Dark" the filter is going to be because I want to calculate how long I have to expose for . Sort of like ND filters have a # based system. ND 1 , ND 6 is there a formula for that? Do I have to find out by trial and error? 720nm = Nd 7? Something like that. I spoke to the conversion people and they don't have such a formula.
thanks,
thanks,