Archived posting to the Leica Users Group, 1997/11/24
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Alf wrote: >Is there a changement in the general consens meanwhile? >I learnt (long long years ago), that the DOF-limits are about 1/3 before >the subject and 2/3 behind. So, I can't explain your -3.2 and +3.3 cm at >f 1.4 from the 1.4/75 mm Summilux. That would be true for an aperture of approximately f/28. As you open up from there the ratio is closer. At f16 it is 2/5th before, 3/5th behind the subject. At f/8 it is 9/20th before, 11/20th behind. As you stop down the ratio shifts the other way. At f/64 it is 3/20th before, 17/20th behind. Without getting too technical this calculation is a function of the _circle_of _confusion_times_lens_aperture_times_focused_distance_ in the divisor of the two equations for depth of field. In the equation for d.o.f. in front of the subject, it is added to the divisor. In the equation for d.o.f. behind, it is substracted. The formula is simpler than I make it sound. It's easy to make a Lotus spread sheet to calculate this for you. Art