It might help photographers concentrate (5)
I believe the answer is:
focus
'concentrate' is the definition.
(I know that concentrate can be written as focus)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for focus that I've seen before include "Point or subject of interest or concentration" , "Concentrate the vision" , "Bull's eye" , "Zoom in (on)" , "Centre of concentration" .)