The profoto d2 duo kit 500500 contains 2 d2 500 airttl heads along with a convenient carry case as the worlds fastest monolights each d2 500 features a flash duration of 163 000 of a second and the ability to shoot up to 20 flashes per second their intuitive interfaces and the ability to adjust the power in 110 f stop increments make these lights ideal for most photographic applications