Nikon NIKKOR Z 400mm f/2.8 TC VR S Lens - Manual (Page 17)

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Lens hood
Lens hoods block stray light that would otherwise cause flare or ghosting.
They also serve to protect the lens.
“Attaching and Removing the Lens Hood” (p.25)
Clamp knob
Use when attaching the lens hood.
“Attaching and Removing the Lens Hood” (p.25)
Parts of the Lens: Names and Functions
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