This should be rather easy for these of you who own and use 0.45 ND or 0.75 ND filters so here we go. Just for fun I'm writing Android app that calculates exposure time when certain filter is applied. Times for 1/2 stops adjustment are easy no problem there. However with 1/3 adjustment where calculated exposure time still less then 30 seconds things get little "interesting".
What would be exposure time with 0.45 ND filter while exposure without filter is 1/1000? Would it be 1/400 or 1/320? (I would have try it on my own but I do not have 0.45 or 0.75 filter and I need to make a decision on it as to get Android app to calculate correctly)