Camera feature (9)
(Another definition for autofocus that I've seen is " feature on camera".)
'camera feature' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for zoom that I've seen before include "Enlarge" , "Change focus smoothly" , "Rush around" , "George --, gave his name to a form of algebra" , "Video communications system" .)