Hello: I have a Canon 7D, and I am not much experienced in photography (yet). What I do mostly is portraits and I would like to buy a flash for indoor portraits... that I can carry wherever I go in a backpack along with the other stuff. I never used one, except for the built in that comes with the camera... What things should be considered when buying one? What technical details should I observe? My budget is not too high, but I dont want to buy something so cheap that would be useless anyway... I know my question is vague... Im looking for some guidance... Any advice?