The shot is ruined, assuming it's still on (4,3)

I believe the answer is:

lens cap

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'the shot' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for lens cap that I've seen before include "protection for photographer" , "Aperture protector" , "Camera cover" .)

I've seen this clue in The Daily Express.

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