Somebody's eyepiece (4)
I believe the answer is:
lens
This could be a double definition.
'somebody's' is the first definition.
Both the answer and definition are singular nouns.
Perhaps you can see a link between them that I don't see?
'eyepiece' is the second definition.
(I've seen this in another clue)
Can you help me to learn more?
(Other definitions for lens that I've seen before include "optical equipment" , "feature of camera" , "town in France" , "Camera component" , "Device to converge or diverge light" .)