HMI Flicker different with new builds

[Nick Gardner]

Ok, I have repeatedly said that red played nice with HMIs. It did. I used magnetic ballasts at 180 shutter with no problems whatsoever on a ton of stuff. On build 17. Now on build 20, 1/48th of a shutter is a no go. You have to use 144 degrees 1/60th.

What changed? It sure would be nice to be able to use 180 again.

I'd love to hear from Red on this. If that's just the way it is, so be it, but it would be nice to know whats going on. Phase issue maybe?

Nick

[Stuart English]

Ok, I have repeatedly said that red played nice with HMIs. It did. I used magnetic ballasts at 180 shutter with no problems whatsoever on a ton of stuff. On build 17. Now on build 20, 1/48th of a shutter is a no go. You have to use 144 degrees 1/60th.

What changed? It sure would be nice to be able to use 180 again.

I'd love to hear from Red on this. If that's just the way it is, so be it, but it would be nice to know whats going on. Phase issue maybe?

Nothing changed Nick.. were you shooting 23.98, 24.00 or 25.00 before, and what are you shooting now?

[Matthew Riggieri]

Nick

I have noticed this too. The color shift under household fluorescent ballasts is also more noticeable. I have found that 1/40 (214 degress) i believe also clean is up if you need more light.

Cheers
Matt Riggieri
Digital Cave

[Nick Gardner]

Hi Stuart,

On build 17, we were shooting 23.98 180degree shutter. Using magnetic and flicker free ballasts. Most scenes all HMIs from6k on down. No problems. Nowadays build 20, if you shoot at 180 degree shutter, 23.98, there is a slow rolling flicker (with mag ballasts). It's not noticeable unless there is a large white wall, or you are looking at a wave form monitor. It's not just my camera. I was operating B-cam on a feature, and both A and B exhibited the problem. The source was an 18k bounce, mag ballast. Also my friend Nate Clapp has noticed the same thing and can only shoot 1/60th to eliminate the roll.

I don't know if it is related, but I am also geting rolling bars at off speed rates with square wave ballasts. 2 different shoots, with 2 different light/ballast combos. I double checked to make sure the ballasts were in "flicker free" not "silent" mode. One was 90fps, no shutter angle could get rid of it, the other was 96fps, same deal.

Any thoughts you had would be appreciated.

Nick

[Stuart English]

Interesting Nick, time to do some digging..

[Nick Gardner]

I'd be happy to shoot some tests and forward you the footage, let me know if I can help. I have a variety of HMIs so I can rule out individual instrument problems.

Thanks,

Nick

[Paul Leeming]

I shot with HMIs two days ago (29.97fps, build 21.3.1, 1/50th relative shutter for Tokyo's 50Hz power) and our high speed stuff also exhibited HMI flicker (120fps slo-mo).

I thought it was just a dodgy ballast but now the emergence of this thread with similar symptoms has me wondering if it isn't something else. Anyway, just adding my voice to say that I noticed it too with the new build.

HTH

Paul

[Guy]

Nowadays build 20, if you shoot at 180 degree shutter, 23.98, there is a slow rolling flicker (with mag ballasts). It's not noticeable unless there is a large white wall, or you are looking at a wave form monitor.

This has always been the case no matter what build. I've seen it since before build 15. It's not usually something that jumps out at you so it's easy to miss.

[Stephen Pruitt]

I really find this thread intriguing, especially since I just bought a 6K HMI with a magnetic ballast. I have not yet shot any footage with an HMI (electronic or magnetic) since moving to Build 21. I'll have to try this out.

Stephen

[Nick Gardner]

Hi Guy, I know it's subtle, but I noticed it as a change. It's very obvious if you are looking at a wavefrom, and on my camera and others I worked with, this didn't use to be the case. There are many many causes for very small HMI flicker, but this seems to be camera related.

Nick

[Dylan Macleod, CSC]

I'm watching this thread. I have a shoot with HMI's later this week and have no time to test.
Dig Stuart - DIG!

[Carlbattreall]

There is an interesting post in the cinematography section about HMI's having issues based on what power source you are using. Maybe that might answer a few questions? maybe not, you guys have way more experience on this subject than me.