Spot of maths anyone? That's inspired by the "Americanisms" thread... but down to brass tacks here. So I proposed this idea years ago and got scoffed and belittled out the door, but I've revisited the idea and I stand resolved that it's useful and good!! The idea is to calculate bellows factor from subject distance. Everyone told me, use the magnification formula, use the bellows draw formula! Well bah humbug to that! Just kidding... but I think it's undeniable that subject distance would be a useful chart to make. Subject distance is much easier to estimate by eye than bellows draw or magnification, and if you had a chart made up for each lens, well it'd be an easy thing to say "for this portrait I need to add 1 stop". eXposure compensation = (bellows draw)²/(focal length)² Magnification = (image height)/(subject height) eXpsoure = (Magnification + 1)² eXposure compensation as a function of subject distance = ?? Your expertise in algebra is much appreciated!