The Nikon SF-1 Ready Light connects to the eyepiece of the Nikon F and Nikkormat cameras. The SF-1 enables you to determine speedlight readiness without removing your eye from the viewfinder. Composition and focusing is allowed while the unit is charging, thus allowing you to be ready to fire when the pilot light turns on (pilot lamp goes out after firing indicating the speedlight has fired). The SF-1 also handles camera-flash sync, eliminating the need for the SC-5/6/7.
The SF-1 accessory unit consists of an adapter (screws into your eyepiece) and two cords coming from the adapter's left side: one cord connects to the camera's PC socket and the other plugs into your speedlight.