Sort of group in centre (5)
I believe the answer is:
focus
'centre' is the definition.
(synonyms)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for focus that I've seen before include "Cynosure" , "Adjust camera lenses - concentrate" , "Concentrate, zero in" , "Adjust for sharp image" , "Zoom in (on)" .)