I've searched the forums for several old posts about this issue but have not found a satisfactory answer. Unarguably, aperture and focal distance (distance between camera and subject) affects the DOF. Many sites, including this one http://www.cambridgeincolour.com/tutorials/depth-of-field.htm, claim that a longer focal length only appears to decrease the DOF than a shorter focal length, but if the subject was to occupy the same fraction of the viewfinder, the DOF would be the same. Obviously, this would mean getting closer with the wide angle or moving farther away with the telephoto. But by doing so, you have changed one critical factor- the focal distance. You are now no longer the same distance away from the subject and since we know for sure that the DOF is affected by the focal distance, does this mean the the focal length DOES have an impact on the DOF?