Nikon D3S - Manual (Page 126)

100
N
The Electronic Rangefinder
If the lens has a maximum aperture of f/5.6
or faster, the viewfinder focus indicator can
be used to confirm whether the subject in
the selected focus point is in focus (the
focus point can be selected from any of the
51 focus points). After positioning the
subject in the selected focus point, press
the shutter-release button halfway and
rotate the lens focus ring until the in-focus
indicator (
I) is displayed. Note that with
the subjects listed on page 98, the in-focus
indicator may sometimes be displayed
when the subject is not in focus; confirm
focus in the viewfinder before shooting.
A
Focal Plane Position
To determine the distance between your
subject and the camera, measure from the
focal plane mark (
E) on the camera body.
The distance between the lens mounting
flange and the focal plane is 46.5 mm
(1.83 in.).
Focal plane mark