What lights cause trouble?

I

Indyreel

Well-known member
Barry,

You mentioned that HMI lights cause trouble with 1/50 shutter. Would this be true of any flashlights?

I know it sounds like a dumb question, but for cost reasons I'm going to be lighting some night scenes with a few handheld 3Million Candle Power spotlights, (modified to plug into an outlet, via a plug-in transformer to bypass the battery/recharging hassle).

Would this setup be problematic for the GH1?
 
Well, let's clarify: it's not the GH1 that has the problem, it's ANY rolling-shutter CMOS camcorder. So what affects the GH1 will equally affect the Red One, the HPX300, the EX1/EX3, the HV20, the HMC40, any of them.

And the particular lights that cause the problem are those that are driven by a magnetic ballast. So we're talking about magnetic HMIs or fluorescents, or mercury-vapor or sodium-vapor streetlights.

Tungsten lights are not a problem. Electronic-ballast HMIs are not a problem. High-frequency electronic ballast fluorescents are not a problem. But if the light runs its ballast at the AC electricity line frequency, then you can have a significant problem with "fluttering waves" or "banding" in CMOS images.

The way to avoid it is to lock your shutter speed to a multiple of the line frequency. In the USA you'd be talking about using a multiple of 120, so a shutter speed of 1/120, 2/120, 3/120, 4/120, or 5/120 should work fine. (i.e., 1/120, 1/60, 1/40, 1/30, or 1/24)

In PAL territories, where the electricity runs at 50Hz, you'd need shutter speeds based on the 1/100 multiples, so 1/100, 2/100, or 4/100. (i.e., 1/100, 1/50, or 1/25)

There is no such thing as an "HMI-safe frame rate" on a CMOS camcorder. That kind of thinking simply does not apply. There are HMI-safe SHUTTER SPEEDS, but not HMI-safe frame rates. In film cameras we used to have certain frame rates that were flicker-free, but in CMOS it's different, you can easily get nasty banding at so-called "HMI-safe" frame rates.

LED lights should be fine.

If you want to know whether you're going to have a problem or not, try forcing an unreasonably short shutter speed, like 1/500, and look at the LCD screen. If you see big thick orange bands scrolling over your image, then yeah, you've got a problem and you're going to have to conform to one of the 1/120-based shutter speeds. For a filmic look I'd choose 1/40, for 720/60p I'd say 1/60.

If you set it to 1/500 and you don't see big orange bands pop up, then you're good to go at whatever shutter speed you want to use.
 
Barry did they plug you into the Matrix and download all this information into your head? Wow man! And thank you very much for sharing, it's been a big help.
 
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Barry,

You mentioned that it's the AC frequency that causes the problem.

I plan on using a DC transformer, wired directly into the hand-held spotlight, instead of relying on the battery. Will this illiminate the AC frequency problem?
 
No, it's not the AC that's the problem, it's that the lights cycle so slowly that they grow brighter and darker during the exposure of a frame. So if you use DC into a fluo, and it's a magnetic ballast fluo, it'll still cycle as slowly.

What kind of light is your spotlight? If it's incandescent or LED, you shouldn't have a problem.
 
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