You can't see the light not going into the camera (obviously) so what you see is some light from the beam being reflected into the sensor. You can't take a pict

You can't see the light not going into the camera (obviously) so what you see is some light from the beam being reflected into the sensor. You can't take a picture of a photon, if that makes sense. So in the double slit experiment you could see the path the light took only if you allowed for a portion of that light to be reflected towards the camera. But then if you did that you wouldn't end up with anything particularly new or interesting as far as I can imagine.