Just a little more detail if you haven't used a graflok beofre. The piece in your picture is the whole back, but contains a graflok back. You need to remove the ground glass. You do that by pressing the #1 clips in the picture below and slide the glass and clips in the direction of the arrow. That gets the glass off. You need to place the light source where the glass you removed isfacing down. It won't be able to hook in the way the glass did, because every camera does that part differently. So when it is in place, the slides that say "Off" that I marked #2 get slid and in the direction of my arrows which slides out hidden slats that hold the intrepid light source in place.