It's impressive when I am in front of the cameras (8)
I believe the answer is:
imposing
'it's impressive' is the definition.
(similar in meaning)
'i am in front of the cameras' is the wordplay.
'i am' becomes 'I'm' (contraction).
'in front of' means one lot of letters go next to another (some letters go in front of others).
'the cameras' becomes 'posing' (I am not sure about this - if you are sure you should believe this answer much more).
'im'+'posing'='IMPOSING'
'when' acts as a link.
Can you help me to learn more?
(Other definitions for imposing that I've seen before include "Taking liberties" , "Dictating; impressive" , "Impressive - or putting tax on" , "Majestic" , "Enormous - levying - striking" .)