Towards the end of the soft and hard light tutorial we looked at the inverse-square law and how larger, softer light sources give more wrap but also have a much faster falloff. We can use this falloff to create black background anywhere such as in the above photo taken in my living room.
This trick takes advantage of soft light’s fast falloff. To get this effect try bringing the largest light source you can get (In my case my softlighter) and bring it as close to the subject as you can manage without getting in the frame (Or if it does get in you can always remove it in post, since we’re making the background black anyways). At first the subject will be overexposed and the background still visible, however if you compensate the subject by dropping the aperture or ISO (Bring the shutter speed to it’s max sync speed), the subject should become properly exposed leaving the background pitch black.
Once this is done just make sure there is enough room for the light to falloff so it doesn’t illuminate any of the background.