A revealing piece of photography (8)
I believe the answer is:
exposure
This clue could be a double definition.
'a revealing' is the first definition.
(I know that exposure is a type of revealing)
'piece of photography' is the second definition.
'exposure' can be an answer for 'photography' (exposure is a kind of photography). I am not certain of the 'piece of' bit.
Can you help me to learn more?
(Other definitions for exposure that I've seen before include "Lack of cover" , "Act of laying open or bare" , "Disclosure (by camera?)" , "Risk for Antarctic explorer" , "O pure sex! (anag.)" .)