So, what works Chris? Do you take an exposure reading without the filter, then mount the filter and adjust the exposure by the number of stops of the filter rating? Or is it more complicated than that? Do you also need to do long exposure noise reduction?
BTW, you have my admiration for not succumbing to the temptation to seek compliments by giving your skys and water that orange/purple Mars look that seems to be so popular.
Later,
Johnny