Ryan E. Walters, Cinematographer

Cinematic Excellence at 24 Frames a Second

Epic + HMI (Mag Ballast)


Just because it works in theory doesn't mean it will work in practice. And just because it works in one application, that doesn't mean it will work in another application - which is why testing durring preproduction is SO important and should NEVER go over looked. I recently spent a day camera testing in preparation for a short film I was shooting for Director Shawn Nelson and it was during one of the camera tests that we stumbled upon some interesting results when shooting with the Epic and HMI's that use a magnetic ballast. What I had thought would be safe speeds on the camera turned out to not be safe at all ...

In addition to referencing the many cinematography apps I carry with me on my phone, I also carry the following two photos which list out the film safe speeds for working with HMI's:

According to these charts, and the charts I have in the apps in my phone, if I follow their recommendations, then I shouldn't see any flicker on screen. However, even as these charts state at the bottom - testing is required to verify results. As you can see from the results in the video above, not all "safe" speeds are really "safe" when shooting on the Epic. I'm not entirely sure of why that is, as there are a number of factors that could be contributing to the problem- it could be the power source, the ballast, the frame rate (23.98 vs 24) or it even could be a result of the way the Epic reads the data off of the sensor. But what I do know is that I am extra glad that these tests were done before the commencement of principle photography, as we could make adjustments before shooting began.

My summation of the test results:
- 24 fps @ Any shutter: Passible, but not 100% flicker free. If used for a short duration, or if the clip is NEVER going to be sped up / time warped in post then 24 fps at just about any shutter rate could be used, as long as the slight amount of persistent flicker is not a distraction to what is on screen. Personally, I would only go with 24 fps and 180 degrees or 144 degrees, as I find the rest to be to unacceptable.

- 60 fps @ 180 degrees: No visible flicker, but waveform shows some present use with caution.

- 120 fps @ 180 degrees: Could be passible, but I wouldn't use it, I find the flicker to be to much.

- 120 fps @ 360 degrees: Much more acceptable then 180 degrees. I do not care for it, but it is useable as long as no time ramping is going to be done in post.

- 300 fps: If you're looking for a disco effect or to cause epilepsy, then sure this *could* be used ...

- In general, it is best to stay away from magnetic ballast HMI's if at all possible. Instead use flicker free electronic ballast for improved results.

Additional Note:
If you are having trouble seeing the flicker, scrub the video back and forth, dark bands appear in the image. That is the flicker, and should not be there. This is particularly trouble some if doing product shots, shooting against large fields of a solid color, or the like.

Until Next Time - Get Out There And Shoot!
Ryan E. Walters, Cinematographer
See Older Posts...