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HMI flicker at 60fps

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Jim Leishman
HMI flicker at 60fps
on Oct 4, 2010 at 1:31:03 pm

I'm shooting a falling object on an EX3 at 60fps under HMI lighting ( flicker free electronic ballasts) drawing power from 50hz mains. What is the fasted shutter speed/ shutter angle I can use before I need to be concerned about flicker. Was planning to shoot with a 90 degree shutter ( effective shutter speed of 1/240) to eliminate blurring of the object. Should I be concerned with flicker at this speed? What would be the fastest shutter speed/ angle I could shoot at ?


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Don Greening
Re: HMI flicker at 60fps
on Oct 6, 2010 at 6:53:50 pm

[Jim Leishman] "Should I be concerned with flicker at this speed?"

Probably. The faster the shutter the more likely there will be flicker. I live in NTSC land and whenever I encounter computer screen flicker I have to lower the shutter speed to 1/50th to get rid of it. You're already on the right track by shooting 60p but you'll have to do a test to see if flicker is going to be an issue. Don't forget about the flicker reduction setting in the EX menu as well.

- Don

Don Greening
Reeltime Videoworks
http://www.reeltimevideoworks.com


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Jim Leishman
Re: HMI flicker at 60fps
on Oct 7, 2010 at 7:21:32 am

Yes as I suspected flicker was indeed an issue at 60fps. Had to shoot 50fps/25p with a 45 degree shutter.
Flicker wasn't horrendous at 60fps and I think it might have been possible to eliminate it in post.
My conclusion is that I don't believe it is possible to shoot at 60fps under HMI lights drawing power from 50hz mains. Please correct me on this if I am wrong.


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john sharaf
Re: HMI flicker at 60fps
on Oct 7, 2010 at 3:34:11 pm

Jim,

Two things:

It is not possible to remove flicker in post. Sorry!

It is possible to shoot 60fps without flicker when HMI's are running on 50Hz current, it's just a matter of using the right shutter speed. There are published tables showing HMI/Shutter Speed windows (look in the ASC Manual) or just use your variable shutter function to scroll through the fractional shutter speeds until the flicker disappears. One caution when doing this is to be careful observing the effect on an LCD as it has a faster refresh rate and can "hide" the flicker. Use the viewfinder in your camera or another CRT device, or a dedicated waveform monitor. These will clearly reveal the presence or absence of the flicker.

JS



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