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At what framerate do lightbulbs start to flicker in slomo?

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Ren Arnol
At what framerate do lightbulbs start to flicker in slomo?
on May 28, 2017 at 8:06:42 pm

Sorry to ask such a basic question, but I couldn't find the answer on the web, and I don't have a camera around... I'm in a PAL country and have to shoot using incandescent lamps (500-1000 Watts). At what framerate approximately does the flickering show? Rather at 80fps already, rather at 120fps, already at 50fps? Thanks!


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Todd Terry
Re: At what framerate do lightbulbs start to flicker in slomo?
on May 28, 2017 at 9:26:03 pm

You really shouldn't have any worry, and should be able to overcrank and shoot at any framerate.

Incandescent blubs (tungsten, halogen, etc.) really do not flicker, so it shouldn't be a concern. They are continuous light sources... they work because the filament inside gets hot enough to also emit light (as well as a lot of heat). Even though the AC power phases on and off, the "off position" is not long enough for the filament to cool and the light to even begin to start to diminish... ergo, the light is continuous and no flicker.

It's the non-continuous light sources that you have to worry about, those that phase along with the AC... such as flos, some LEDs (although usually only those that are AC powered, not battery or DC LEDs), HMIs, etc.

You should be good to go.

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Ren Arnol
Re: At what framerate do lightbulbs start to flicker in slomo?
on May 29, 2017 at 7:50:46 am

Hi Todd, thanks for your answer! I made the experience though, that when shooting with the maximum 180fps of my FS7, even incandescent lights show a noticeable flicker. I just never tried at what framerate the flicker starts...


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Todd Terry
Re: At what framerate do lightbulbs start to flicker in slomo?
on May 29, 2017 at 6:02:53 pm

Hmm... that's odd. You should really never have to worry about flickering with a continuous light source, like tungsten instruments.

BUT...

When dealing with non-continuous sources, keep in mind that flickering might occur not necessarily because a frame rate is too high, but just that it is wrong for the particular light source. It just depends on how your shutter is syncing with the phasing of the power source. So, if you get flickering at one particular frame rate, you might eliminate it by going a bit slower... but you also might have just as good (or better luck) with increasing the frame rate a bit. So it's not necessarily that the flickering starts at a particular speed and everything above that flickers... there are probably various rates along the way that you'll run into trouble, but things are fine on either side of that.

And also... we've been purely talking about frame rates... just as important (or maybe even more so) is shutter speed, which is of course a completely different thing from frame rate. If I ever experience flickering, it's shutter speed that I adjust, not frame rate. I'm not really familiar with your camera, but if it has a "clear scan" mode where you can adjust shutter speed by hertz rather than by fractions of a second or shutter angle, then you can use that to help eliminate flicker (especially at more "normal" fps).

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Rick Wise
Re: At what framerate do lightbulbs start to flicker in slomo?
on May 29, 2017 at 6:14:29 pm

And don't forget shutter angle..... That too, on some cameras, can be adjusted to eliminate or create flicker. Takes a camera with a true shutter that is variable.....

Rick Wise
Cinematographer
MFA/BFA Lighting and Camera Instructor Academy of Art University
San Francisco Bay Area
http://www.RickWiseDP.com


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Ren Arnol
Re: At what framerate do lightbulbs start to flicker in slomo?
on Jun 2, 2017 at 10:58:31 am

I'm finally at home (Berlin, Germany, so 50Hz) and gave it a try: in my test, ordinary light bulbs DON'T flicker at 100fps and 125fps, anything in between or above (also at 150fps and up to 180fps, where my camera stops) flickers. I also tried variable shutter speeds, but that didn't influence the result, so a 180° angle is fine. With higher framerates, the FS7 doesn't allow me to adjust the framerate framewise, but in slightly bigger steps, I could image, that 149fps or 151fps might be flicker free as well, but I couldn't try.


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Robin Probyn
Re: At what framerate do lightbulbs start to flicker in slomo?
on Jun 23, 2017 at 8:00:22 am

Tungsten lights do actually flicker and are not continuous .. they heat up and cool down.. the way to get rid of tungsten flicker is to have big light sources .. then the larger filament never actually cools down that much.. above 2K is safe.. ordinary bulbs will give you flicker as the filament is small..



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Ren Arnol
Re: At what framerate do lightbulbs start to flicker in slomo?
on Jun 27, 2017 at 7:18:31 am

... and the size of the filament is probably the reason why there is no easy answer to the question, at what framerate the flicker starts being visible...


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Robin Probyn
Re: At what framerate do lightbulbs start to flicker in slomo?
on Jun 27, 2017 at 8:13:20 am

yes sorry cant answer that .. but pretty easy to shoot some test I would think.. as you did.. its a common mistake to think that tungsten lights wont flicker at HFR ,compared to the more obvious suspects.. the way around it is big lights.. big filament, that never has time to cool down enough..



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Mathew Farrell
Re: At what framerate do lightbulbs start to flicker in slomo?
on Aug 11, 2017 at 5:33:54 am

A purely accademic answer here, but I'm with Todd - it's not the frame rate, but the shutter speed. Shutter angle is just another term for exactly the same thing, and generally anachronistic these days (don't misunderstand me, I prefer working in shutter angle). Same goes for clear scan - doing the same thing, but on a different measurement scale, and possibly different resolution.
The size of the filament should affect the severity of flicker, as others have suggested, but shouldn't change the shutter speed at which it is visible. I don't know how accurate the stated AC cycle speeds are (i.e. 48Hz and 50Hz), but multiples of these speeds should be fine, and anything that's not a multiple should induce flickering. The severity of the difference and the size of the filament should both play a part in how noticeable it is. I guess figuring out these multiples is a good reason to be working if fractions of a second rather than shutter angle.

*EDIT*
Now I've typed out the above, it occurred to me that it should be the frame rate, not necessarily the shutter speed that shows flickering, since frame rate is the clock speed, for want of a better phrase, of the camera. The shutter speed is a slave to the frame rate. I guess if you're on a flicker-pronse frame rate, dragging or closing the shutter a bit spans different AC cycles and averages out the flicker. How's that sound?

Mathew Farrell
flowstate.com.au


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