Yup, closer than that and it's guess or measure. The M3 only tracks the rangefinder to about 1 meter. The 21 has enough depth of field so it really isn't a problem. Depth of field isn't based on an absolute, it's based on what the manufacturer considers acceptable unsharpness. A cheap off brand lens might have markings showing more depth of field than an expensive lens. It might even appear to have more depth of field because the point of critical focus has a softer image ~ there's nothing really crispy sharp to compare with. The Super Angulon has superb central sharpness. Newer designs tend to have better corner sharpness but it seems to come at the expense of a bit of central sharpness. On the plus side the Super Angulon has less distortion than any other ultra-wide angle lens.
Also keep in mind that distances are measured from the film plane, not the lens flange or front of the lens.
