The Nikon SF-1 Eye Piece Lamp Fits the eyepiece of the Nikon F and Nikkormat cameras. You can determine speedlight readiness without removing your eye from the viewfinder, you can compose and focus while the unit is recycling and be ready to take a photo when the pilot light comes on. The pilot lamp goes out after firing.
It consists of an adapter that screws into your eyepiece and two cords coming out of the adapter's left side: the top one is connected to your camera's PC socket, and the bottom one has a pronged plug to go into your speedlight. Thus it also handles camera-flash sync, obviating the need for the SC-5,6 or 7.