I recently ran into a bit of flicker trouble shooting under Arri HMI Fresnels with normal flicker-free ballasts at 240fps with the epic.
I know there are special high speed ballasts. I was reading AC's interview with Manuel Alberto Claro for Melancholia, for which he says he used high-speed ballasts for the Phantom work in the intro of the film, "Because although the normal ones are flicker-free, when you get to 1000fps, they're not!"
Above what frame rate are high speed ballasts recommended?
There are obviously people on this forum who do a lot of epic work - do you always order high-speed ballasts for your HMIs when doing high speed stuff?