Lens we’re adapting for one once seen in cinemas (8)
I believe the answer is:
newsreel
'one once seen in cinemas' is the definition.
(newsreels were once shown in cinemas)
'lens we're adapting' is the wordplay.
'adapting' is an anagram indicator.
'lens'+'were'='lenswere'
'lenswere' is an anagram of 'NEWSREEL'.
'for' is the link.
(Other definitions for newsreel that I've seen before include "Film report" , "Film giving reports" , "Cinema broadcast" , "information screened" , "Short film of current events" .)