Yongnuo YN-468 II i-TTL Speedlite Flash With LCD Display, for Nikon (Discontinued by Manufacturer) S1/S2 Mode: This modes are applicable for slave flash in order to create many light effects. Test Flash: Whether in any mode, you can press PILOT button to test if the flash light flashes normally. Set the Focus Position of the Light Head Manually. Multi-lamp Lighting Application: Use inbuilt flash or top-mounted flash as master flash. Rear-curtain Sync: You can use slow-speed shutter to produce trailing smear for the object and the flash light will flash at the moment when the shutter is going to be shut.