Good deal of vision? (5)
I believe the answer is:
sight
I believe this clue is a double definition.
'good deal' is the first definition.
(I've seen this before)
'vision?' is the second definition.
('sight' can be a synonym of 'vision')
'of' acts as a link.
(Other definitions for sight that I've seen before include "Observe" , "Spot - eyesore" , "object of especial interest" , "Show" , "Spectacle; aiming aid" .)