There always seems to be much confusion about this subject, with people commenting about theory but without any data. Well, here are some data from my lens DOF scales, both 6x7 and 35mm. I'm comparing lenses of similar magnification. The P67 300mm will equal a 135mm Canon in DOF when the 300 is at f/45 and the 135 is at f/16. Three stops is a big difference when shooting in windy conditions. Yes, the magnifications are slightly different on these two lenses so I'll give another example; the P67 600mm vs. the Canon 300mm. There is nearly a three stop difference in DOF on these two lenses with the Canon 300 having more depth. DOF was about the same when the 600 was at f/45 and the 300 was at f/16.

-- Steve Rasmussen (srasmuss@flash.net), August 07, 1998