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FLUORESCENT FLICKER


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#1 James Mann

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Posted 03 July 2008 - 08:43 AM

Shooting in a Super Market and would love to have the overhead Fluorescents pulsating noticeably.

Would adjusting the SHUTTER ANGLE do anything for me?

Shooting on a PANAFLEX 16. So our shutter is adjustable from 200 degrees to 50 degrees. There is some synch sound so adjusting the speed may not work.

Another option I suppose to make the key light flicker/pulsate somewhat. But it would seem a lot more motivated if the rest of the store had a sort of pulsating to it.

Thanks

James
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#2 Matthew Parnell

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Posted 04 July 2008 - 07:20 PM

If they are induction ballasts you can dimm them to make them flicker. Keep in mind you should only do this during the take as ballasts dont particularly like this kind of treatment.

Squarewave ballasts will not flicker when dimmed.
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#3 James Mann

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Posted 06 July 2008 - 05:52 PM

MATT,

Thank you, that is a good idea, but let's imagine that I am shooting in a supermarket with hundreds of overhead fluorescents fixtures. I have no way of dimming each unit individually and putting a dimmer somewhere in the store's power main doesn't seem feasible.

Is there something that I can do on the camera that would help me achieve the effect I am looking for?

Thanks

JAMES.
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#4 David Mullen ASC

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Posted 06 July 2008 - 05:57 PM

With 60 Hz discharge lighting, at 24 fps crystal, you have a window of acceptable shutter speeds that is pretty broad, so changing the shutter angle won't really get you the effect you want. You really need to change the frame rate and shutter speed together, like play around with 23 fps or 25 fps at different shutter angles to find something really noticeably "bad". Otherwise all you may see is a faint color shifting more than a flicker.

It's easier to do this with a video camera where you can see the results immediately. Otherwise, shoot a test under any standard 60 Hz discharge lighting that uses magnetic ballasts. You might be able to just shoot a test at Panavision at different frame rates and shutter angles. Or if you don't have time for tests, borrow a Genesis camera there at Panavision during your prep day and play with the frame rates and take some notes.
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#5 James Mann

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Posted 06 July 2008 - 09:22 PM

DAVID

Thanks for the timely reply.

I will be shooting a test tomorrow and will try out the 23 fps and 24 fps and a few different shutter angles.
I think that there may be some synch sound in the scene that I am trying to achieve this effect for so changing the fps may be a problem. But I'll talk to sound and see what he's got to say about the matter.

I'll post about the results...

Thanks Again.

JAMES.
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#6 Maya Bankovic

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Posted 06 July 2008 - 11:13 PM

Hi James,

Please do let us know about your results, I'm trying a similar effect and have been thinking about different ways of achieving it. I'm thinking more along the lines of a sporadic off-and-on flicker, but I'd also like to have some fluorescents continuously pulsating somewhere in the scene (a locker room).

Thanks for your question!

Maya
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#7 James Mann

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Posted 11 July 2008 - 08:58 AM

Unfortunately, The Flicker Tests proved inconclusive.

Attempted:

23 fps @ 190 degree
23 fps @ 170 degree
25 fps @ 190 degree
25 fps @ 170 degree

Found nothing. Though the rest of the test went pretty well...

Oh, the scientific method.

James.
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#8 John Sprung

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Posted 11 July 2008 - 01:21 PM

Flourescents give you 120 fairly wide pulses of light per second, with narrower gaps between them. To get flicker, you need to have some frames exposed mostly during a gap in the light output, which means having to go to a very small shutter angle. Test at 50 degrees, since that's the smallest you have available, and also at 90, 120, and whatever you want to try. Be aware that really short shuttering will cost you the illusion of motion because there isn't enough motion blur. Depending on the speed of your camera moves and action, the reasonable cutoff point is probably in that 90 to 120 range.

Shooting at 24 fps, you'd have 5 light pulses per frame, and there'd be no variation from frame to frame. By going just slightly off speed, you get a very slow pulsation. For instance, the TV rate 23.976 should give you a pulsation every 42 seconds. Going up to 25 fps gives you 24 light pulses in 5 frames, so your pulsation would happen every 5 frames. You could shoot sync at 25 like they do in the 50 Hz countries that way. For pulsation rates in between those, just pick a speed between 24 and 25 fps.

One more wild card to consider: Does your location have single phase or three phase power? All of the above is for single phase, which is what we all have at home. Large commercial and industrial buildings, though, can have three phase power. It looks to the camera like three different single phase systems equally spaced in time. In that case, only one third of your overhead lights would be on a gap between pulses at a time. Three phase gives you much more even power, which is really nice for big industrial motors, but exactly what you don't want for this shoot.




-- J.S.
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