Form taken by film when you spool up? (5)
I believe the answer is:
loops
'form taken by film when' is the definition.
I can't judge whether this defines the answer.
'spool up?' is the wordplay.
'up?' is a reversal indicator (in down clue: letters go upwards).
'spool' backwards is 'LOOPS'.
'you' acts as a link.
Can you help me to learn more?
(Other definitions for loops that I've seen before include "Oval-shaped single coils, in a piece of thread perhaps" , "Twists" , "Winds" .)