Canon EF 400mm f4 DO IS USM - Manual (Page 11)

ENG-10
The dedicated Lens Hood ET-120 helps to
prevent stray light from entering the lens and
protects the front of the lens from rain, snow or
dust.
To attach the hood, loosen the hood locking knob
by turning it counterclockwise. Fit the hood onto
the lens hood mount, and tighten the locking
knob to fix it in place. Use the same procedure,
in reverse, to remove the hood.
8. Hood
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