Briefly visible through lens, river captured (2,5)
I believe the answer is:
in short
'briefly' is the definition.
('in short' can be a synonym of 'briefly')
'through lens river captured' is the wordplay.
'through' becomes 'in'.
'lens' becomes 'shot' (I can't explain this - if you can you should believe this answer much more).
'river' becomes 'r'.
'captured' indicates putting letters inside.
'shot' going around 'r' is 'short'.
'in'+'short'='IN SHORT'
'visible' acts as a link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for in short that I've seen before include "to be brief" , "To sum up, briefly" , "Concisely" .)