Urgent: Help with eliminating Flicker with Epic at 120fps

[Jean Déraps]

I'm presently on set with my Epic and with ArriSun 1.2K flicker free HMIs and I'm getting flicker.... according to my calculations and experience this should be completely flicker free! Does anyone have any suggestions as to why I'm getting flicker?

 

[Justin Marx]

Have you tried changing your shutter to make it work for now?

 

[Jean Déraps]

Yes, I have tried different shutter speeds, despite the fact that at 120fps all speeds should be flicker free....

 

[Anders Holck]

In my experience Flickerfree HMI's are not immune to rolling shutter artifacts. ARRI makes special HS ballasts which is pretty stabile even at 2200 fps, but you can still experience magenta/greeen phasing at some speeds.

Normal "Flickerfree" is between 75-300 HZ Square wave.
Highspeed Flickerfree is 1000 HZ Square wave.

 

[Kenneth Williams]

I don't know where you are located but here is my try: Check your numbers again:

50 Hz Speed in fps at any Shutter Angles :-

100.000 50.000 33.333 25.000
20.000 16.666 14.285 12.500
11.111 10.000 9.090 8.333
7.692 7.142 6.666 6.250
5.882 5.555 5.263 5.000
4.761 4.545 4.347 4.166
4.000 3.333 3.125 2.500
2.000 1.250 1.000


60 Hz Speed in fps at any Shutter Angles :-

120.000 60.000 40.000 30.000
24.000 20.000 17.143 15.000
13.333 12.000 10.909 10.000
9.231 8.571 8.000 7.500
7.058 6.666 6.315 6.000
5.714 5.454 5.217 5.000
4.800 3.750 3.000 2.500
2.000 1.875 1.500 1.000

Check your playback framerate.

Shoot test @ normal frame rate. Example 23.98. To see if flicker persists.

Check all globes one at a time.
Make sure ballast is set to flicker free silent

 

[Jean Déraps]

Thanks for your input.... I think we solved this. Just for your info, there was a small fluorescent lamp high up (25 feet) on the ceiling to the rear that someone lit up (i'm on location) that was overlooked....since we had so much HMI light (and there are windows on that side) no one noticed but it was screwing up with flicker big time!

I was so puzzled I was looking for complicated solutions when in fact it was so simple... this stuff happens!

Thanks for your help and input...

 

[Hudson Tanimoto]

Also the onboard monitoring on the Epic can't be trusted when it comes to flicker. I've seen the monitor look completely flicker-free and then see heaps of flicker when watching the footage back in RCX

 

[Jean Déraps]

Just to chime back in....the problem wasn't actually the fluorescent lamp.....but 2 (not 1!) defective HMIs... we called the rental shop, had them replaced and the problem was solved. Part of the eye-brow-raising was that I didn't expect that *2* HMIs would be flickering.... I guess one has to expect the unexpected! So be careful with these so-called flicker free HMIs and make sure you test them before assuming they work properly....

 

[Stephen Williams]

Just to chime back in....the problem wasn't actually the fluorescent lamp.....but 2 (not 1!) defective HMIs... we called the rental shop, had them replaced and the problem was solved. Part of the eye-brow-raising was that I didn't expect that *2* HMIs would be flickering.... I guess one has to expect the unexpected! So be careful with these so-called flicker free HMIs and make sure you test them before assuming they work properly....

Time to change rental house I think

 

[Jean Déraps]

Stephen, you don't want to know what I think about this rental house...and not just because of the problem I had this time. But I played no role in deciding who we'd rent from.

 

[Justin Marx]

Time to change rental house I think

Or make sure someone checks the stuff out.. a slight flicker in an HMI sometimes is a hard one to spot..