Heard first person, quiet, get a lens (8)
I believe the answer is:
eyepiece
'a lens' is the definition.
(eyepiece is a kind of lens)
'heard first person quiet' is the wordplay.
'heard' shows a homophone (sound like).
'first' becomes 'i' (I in Roman numerals eg Elizabeth I).
'person quiet' becomes 'piece' (I am not sure about this - if you are sure you should believe this answer much more).
'i' is a homophone of 'eye'.
'eye'+'piece'='EYEPIECE'
'get' is the link.
Can you help me to learn more?
(Other definitions for eyepiece that I've seen before include "Top end of a microscope" , "that fits into socket" , "It enables us to view" , "Lens(es) at the viewing end of an optical instrument" , "Astronomer looks into this" .)