What are the lens design assumptions behind DOF equations? I ask because I have just acquired a lens to which the standard equations apparently don't fully apply, if at all. The manual for the lens, a Wollensak f6 10" Veritar, states as follows:
"With a conventional, anastigmat type lens it is customary to focus on the catch lights of the eyes, because there is a range of sharpness both in front and behind the plane focused on. This range of sharpness or depth is small at large apertures."
"With the Portrait Veritar there is no usable depth of field in front of the plane focused on. However, because of the particular design of the lens, there is considerable depth behind the plane focused on. Within this region there is a considerable amount of recognizable detail."
Does this mean that standard DOF equations don't apply at all? Do they apply but only for far depth of field? Do they apply for both near and far depth of field as the lens is stopped down? Stroebel, in the 5th edition of his book, talks about soft focus lenses and specifically about designs in which there is no depth of field in front of the plane of focus, but he does not address the calculation of depth of field for these lenses.