Shutter and flourescents

F

firehawk

Veteran
I havent ran into a problem with this yet but I've also been shooting 1/60 shutter most of the time through the years. I'm in the USA.
If I'm shooting in a room with flourescents or questionsble lighting need I avoid shooting 24p 1/48 shutter and instead stay with 1/60 to avoid the risk of flicker?
The reason to go to 1/48 would be for extra light, but I don't want to risk a problem.

Is 1/60 always the safe way to go?

And would I be able to tell on the camera LCD if there was a problem or would it only show up once I'm back in post and it's too late?

In a conference lecture I could also shoot 30p or 60p also but there wont be any action happening.
 
In the U.S. don't shoot 1/50 or (1/48). In countries with 220V, shoot 1/50. You've been shooting 1/60 in the U.S. and that is correct. The frame rate itself is not important.
 
firehawk said:
If I'm shooting in a room with fluorescents or questionable lighting need I avoid shooting 24p 1/48 shutter and instead stay with 1/60 to avoid the risk of flicker?
Click to expand...

Any discharge lighting, including fluorescent, LED, HMI, carbon arc, etc. varies as a function of discharge frequency. In the case of magnetic ballasts, they vary as a function of power line frequency. In this case, 60Hz. Most cheap building fluorescent lighting uses magnetic ballasts, but as time moves forward more and more of them are electronic "flicker free" ballasts, which use higher discharge frequencies.

In any case, the safest thing to do is to expose each frame during the exact same part of the cycle -- so each frame gets the exact same exposure, and capture artifacts are minimized.

So... if you think your fluorescents are firing at 60Hz, how do you record artifact free images? Hmmm... one would think that an even multiple of the firing frequency would work, yes? So 1/30, 1/60, etc. Not 1/24, 1/48, or 1/50. Try it, see what you get.

Also, what about frame rate? You think 24fps will work better or worse than 30fps? Why? Try it and see.
 
Also, if the light uses pulse modulation for its dimming (like many LED lights do), you're not going to be able to overcome that with shutter speed! Some dimming LEDs are going to screw up CMOS footage no matter what, and the only way to make them safe is to shoot with them at 100% brightness at all times.
 
In North America, the power system is 60Hz, that's 60 cycles per second. With every cycle there's a positive and and "negative" part of the cycle. Thus, with fluorescent and neon lights they pulse twice per cycle or 120 times per second. LED Lights are a special problem that I'll cover later.

In an ideal setting we want to capture an even number of pulses. 120/1 (1/120 shutter), 120/2 (1/60 shutter), 120/3 (1/40 shutter), 120/4 (1/30 shutter), and 120/5 (1/24 shutter). This would prevent any beat frequency from occurring in the brightness in the image.

AC Powered LED Lights present a special problem, because LEDs only light when the current flows 1 direction. Depending on who designs the LED Light, this may have 120 light pulses per second OR it may have 60 light pulses per second. There's no way of knowing until you shoot and look at the video.

To be on the safe side, assume it's 60 light pulses per second for an LED: 60/1 (1/60 shutter) & 60/2 (1/30 shutter).


50Hz Power:

The rules are the same, only the numbers change: 100/1 (1/100 shutter) & 100/2, (1/50 shutter).

For LEDs, just use a 1/50 shutter.



Bob Diaz
 
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