high speed ballasts / 240fps epic

[Lorenzo Levrini]

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?

Thanks.

 

[Andy Jarosz]

What a ballast is doing when you click it to flicker free is changing from 60 to 75Hz. Usually manufactures say this will allow flicker-free filming up to ~150 fps. It's not necessarily for high speed stuff, more for off speed stuff. The flicker-free mode also introduces a slight whine.

The high speed ballasts have a much higher refresh rate, the specific number depends on the ballast you're using but usually covers most high speed stuff. Of course, everything has it's breaking point and you'll always get flicker at some frame rate--but not at anything the Epic is capable of.