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HMI Flicker With The Alexa & Epic

Posted by Ryan E. Walters on 29th Jul 2012

I’ve been shooting a lot of high speed content with the Alexa and the Epic lately and I have uncovered some unexpected results when shooting with both cameras. Watch the 2 minute video, and then read on to learn more about what is going on.
my testing of the Epic with magnetic ballast HMI’s my results were as I expected – multiples of 60 were the most flicker free settings to use, and in general it is best to avoid magnetic ballast HMI’s. So it surprised me when I saw flicker from the Epic when I was shooting at supposedly safe settings using flicker free electronic ballast HMI’s. People like Art Adams have explained and documented that a frame rate of 23.98 and a relative shutter speed of 180 degrees is not flicker free. Applying his experience, and making choices based off of well published charts is a safe place to start from, but the final word on the matter can only come through hands on testing and experimentation as I found out on this production. Regardless of what the numbers say, always test and verify.

What I find perplexing:
- According to the charts, if I am shooting at 120 fps, I should be able to use any shutter speed I want. However, with the Epic, in the example above, I was only able to get a flicker free image at 360 degrees*.

- If the flicker in the Epic was a result of the 23.98 project time base, then I should still see the flicker in the Alexa as it had the same time base at 120 fps.

Continue reading on Ryan’s blog