Mamiya 645 PRO TL - Manual (Page 26)

Depth of Field
Reading the Depth of Field Scale
Depth of field is defined as the zone
of sharpness before and behind the
plane of focus. It depends on camera
subject/distance, focal length of lens,
aperture setting and distance the lens
is focused at.
16 22
In addition to visual observation, the
Depth of Field can be determined by
using the Depth of Field Scale on
each lens. f/stop numbers appear on
both the right and left side of the red
index mark in the center of the scale
ring. Simply read the figures which
appear above the f/stop numbers on
the distance scale of the lens.
For example, with the 80mm f/2.8N
lens focused at 3m and the aperture
set at f/22, the depth of field scale
indicates that the zone of sharp focus
will extend from about 2m to 6m.