Used for TTL auto exposure control when using SB-16B, 20, 21B, 22, 22s, 23, 24, 25, 26, 27, 28, 28DX, 29, 29s, 50DX, 80DX, 800 at a distance of approximately 1.5m from cameras such as D2H, D1 series, D100, F5, F100, F80, U, and FM3A. When attached to the SB-800, the AF assist light function can be used.