Crack marksman gets exposure (8)
I believe the answer is:
snapshot
'exposure' is the definition.
(snapshot is a kind of exposure)
'crack marksman' is the wordplay.
'crack' becomes 'snap' ('snap' can be a synonym of 'crack').
'marksman' becomes 'shot' (I've seen this in other clues).
'snap'+'shot'='SNAPSHOT'
'gets' acts as a link.
(Other definitions for snapshot that I've seen before include "Pan hosts over casual photo" , "Instant record of an event" , "still taken quickly" , "Quickly taken photograph" , "Picture" .)