Nikon f2 - Manual (Page 50)

MIRROR LOCKUP
The reflex mirror must be locked in the up position
when using either the Fisheye-Nikkor 6mm f/5.6 or the
OP Fisheye-Nikkor 10mm f/5.6 lenses, since their rear
elements protrude into the camera body and interfere
with mirror movement. Locking-up the mirror is also
necessary when shooting with a motor drive unit at its
top speed setting. To lock up the mirror, depress and
hold the depth-of-field button and turn the mirror lock­
up lever downward until the white dot is aligned with
the white index line. The mirror will remain in the up
position until the lever is returned to the normal posi­
tion.
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