Canon EF300mm f/2.8L IS II USM Instructions Manual page 16

11. Fitting the Lens Cap
Reverse the lens hood, slip
it over the lens, and tighten
the lock knob to fix it in
place.
Lift the hook and loop
fastener, and fit the cap so
that the lock knob rides up
the slot in the cap.
With the lock knob at the
opening in the cap, close
the fastener to fix the cap in
place as shown.
Can also be attached to the
O O
front of the hood when using
the lens.
ENG-15