Nikon Camera F3AF - Manual (Page 66)

Backup Mechanical Release Lever ®
This lever is provided as an alternative method of releasing the
shutter in case the camera's batteries become weak or com­
pletely exhausted. To operate the lever, first use your fingernail
to pull it down to the ready position. Then push it down to trip
the shutter. The shutter operates at a mechanical speed of
approx. 1/60 sec. at any setting on the shutter speed dial, except
T. At T, push down the backup mechanical release lever with
the power switch @ off.
Caution: If you advance the film while holding down the backup mechan-
icat release lever, the shutter will fire immediately at the completion of
the film advance stroke, thus wasting a frame. Also, if you fail to advance
the film completely and then use the lever to trip the shutter, the mirror
® will remain in the "up" position; when the additional stroke is made to
complete film winding, the shutter will lire, also wasting a frame.