I've read carefully, but here's a question about Les' method: what if i want to do a certain number of exposures instead of having a certain shutter speed i want to go for? How would i divide the original exposure?

e.g. dividing 1/125 into three exposures.

Would i shoot three exposures of 1/45 [three stops down of 1/125 for each of the three exposures] or divide 125 by 3 and match it with the closest shutter time?