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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Fast shutter speeds at 24fps under HMIs

E

egustavo

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Maybe I'm using the wrong search criteria but I've been digging around the forum but most info about safe shutter speeds deals with shooting off-speed for slow motion. Last night we shot some footage at 24fps (23.98) using HMI lights with electronic ballasts but wanted a high shutter speed of 1/192 (45°). We got flicker in our image that I was only able to fix by changing the Shutter settings to Syncro and adjusting that setting. I don't remember exactly but I believe after adjusting the Syncro we ended up with 1/120 (72°) shutter which ened up being acceptable for our purposes.

Even though it corrected the problem of flicker, is adjusting the Syncro the right/best way of eliminating the flicker we saw in our image? Thanks in advance...
 
Were your ballasts set to "flicker-free"? What was your shutter set to when you got the flicker - "normal" or "relative"?
 
All ballasts were set to flicker-free. The shutter was set to 1/192 and then shutter mode was set to Syncro. The Syncro was set until the flicker in the image was eliminated and this, in turn, altered the shutter speed to 1/120. All the footage was shot at 24fps, it's the shutter that we wanted to change and ranged from 1/48 to 1/192.
 
I think if your ballasts are set to flicker free you should certainly be able to film off-speed or with higher shutter speeds (up to a limit) - I'm not too up on all things 60Hz-related but isn't 24fps under 60Hz light meant to be safe for pretty much any shutter angle?

What I was trying to ascertain earlier was when you originally got flicker did you try changing the shutter setting from "relative" to "normal" or vice versa, or do you not remember what the shutter was originally set to before you changed it to "syncro"?
 
I'm wondering if there might be an issue with the ballasts.

I'll add that one of the nice things about Red, is wysisyg as far as flicker, so if there is and issue, you're aware of it at the shoot, and not surprised later on in the editing suite.
 
David - I was in Shutter>Normal setting when I saw the flicker and then switched over to Syncro (in a panic and not sure if it would work to be honest) and adjusted it till the flicker went away. We were in a rush so the next time we used a high shutter, I don't know if we used the same Syncro setting.

jimarrik - It seem to be happening with both our 4K HMI and 1.2K HMI and when plugged into house power and when running off our genie. Also, it didn't happen when we shot at 1/48.

We're shoot again this week with several days where we'll need to shoot under the same HMI's - I'll keep an eye out and see if it happens again.
 
Usually HMI ballasts have a "normal" or a "silent" mode, which is used for sync sound shooting and makes the ballast and head a little quieter. The other option is "flicker free".

I would ensure that you are on flicker free.

Actually, thinking about it again, I can't remember if magnetic ballasts have this feature. I have only used electronic ballasts recently...
 
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