Old film about tango that shows right amount of spirit (5)
I believe the answer is:
optic
'that shows right amount of spirit' is the definition.
(device for measuring alcoholic spirits)
'old film about tango' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'film' becomes 'pic' (short for picture).
'about' means one lot of letters goes inside another.
'tango' becomes 'T' (phonetic alphabet: alpha, bravo, charlie etc.).
'pic' placed around 't' is 'ptic'.
'o'+'ptic'='OPTIC'
(Other definitions for optic that I've seen before include "Relating to the eyes" , "Picot (anag.)" , "What could measure the spirits" , "Pertaining to the eye" , "Alcoholic drink dispenser" .)