The large ExpoImaging Ray Flash Universal Ring Flash Adapter allows you to convert your shoe-mounted flash unit into a ring light. It does this by clamping onto your flash head and then using a system of prisms and mirrors to guide the light into the ring unit creating an even, diffuse light source. This Ray Flash attaches to your system by clamping onto the flash head and extending down around the lens. This size adapter is compatible with systems measuring between 6.9-7.5 from the flash head center to the lens center due to the adjustable mounting options. It will fit over lenses up to 3.75 in diameter. Also, included with the Ray Flash is a black, rubber O-ring for ensuring your flash head stays in the appropriate positions without sagging.