Shooting very high speed with hmis

[Nick Gardner]

Hi,

 

I know all of the theory, I have a long history of shooting at high speeds, both on film and digitally.

 

I am interested in peoples real world experience working with flicker free ballasts.

 

I had a job today where we intended to shoot with the studios Hive plasma lights. On a test day it was determined that they didn't have enough oomph to get an exposure at 930 fps (Phantomflex 4k). I had previously tested a modified ETC source 4 par with a 575 HMI globe and a german electronic ballast and found it to bee flicker free. Going tungsten was not an option, so on short notice we used 7 of the 575 fixtures.

 

Initial set up was a 3/4 key 6x6 silk with 3 of the 575s punched through that, double edges one 575 each, and fill being another bounced into a 4x4 muslin. That put us at a t1.3 at 800iso 930fps 360 shutter.

 

We rolled like that for the first half of the day. There was no pulsing, strobing, rolling bars, or other cyclical artifacting. Shortly after lunch we switched to a longer lens that was a 2.8 so we pulled some diffusion and marched some stuff in. The foreground lights were fine, but the light on the background was flickering a little bit. Again, not a cyclical thing but more wandering. We were unable to make it go away by swapping out heads or changing power to different circuts. As we were tighter we replaced that instrument with one of the plasma lights and marched it in. This got rid of the majority of the problem, but when looking at the waveform monitor, you could still see it jumping around a bit (but within acceptable levels.

 

That was the only problem we had all day. I understand that there are no guarantees with HMIs and high speed, yadda yadda, but my gaffer and I are trying to track down the source of the issue since we were fine most of the day. I am wondering if since the light that was causing a problem was with a spot lens and no diffusion, and by it's self, if it could have been arc wander, but the fact that the Hive still wasn't solid makes me wonder if it was mains harmonics or some other voodo.

 

Any thoughts or opinions would be apreciated.

 

Cheers,

 

Nick Gardner

 

PS- The ballasts are Mitronics and are PFC