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Sony NXCAM NEX-FS700 CineAlta
4K EXMOR sensor with SDI, slow-motion recording.


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Old July 6th, 2012, 06:53 PM   #1
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The flicker thing.

I picked up my fs700 last week, the day before I went upstate for vacation. I had a great time "playing" with it. Shooting with the high frame rate is seriously addictive though. I really didn't mean to, but probably spent 97% of my time with the camera shooting at 240fps.

Anyway, my outdoor stuff looks nice. But, there is definitely a noticeable flicker when shooting at a high frame rate using any sort of practical indoor light source. And, of course, this is an issue with the high frame rate and heat fluctuations with the bulbs, not anything that is specific to this camera. But, it's going to me an issue for me.

I shoot a lot of food related stuff, in restaurant kitchens, etc. There are going to be all kinds of horrible overhead lights. Sometimes I have control over the overhead lights, sometimes I don't.

My understanding is that the flicker goes away or is reduced if using more powerful lights (1K and over) and possibly LEDs, which have a faster refresh rate.
I will test the LED thing at some point, but using 1Ks probably isn't practical for me.

If anyone has any experiences, recommendations, etc. to share, it would be great to hear them.

Here is something I shot quickly using a household incandescent light bulb. The flicker is pretty noticeable.

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Old July 6th, 2012, 07:06 PM   #2
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Re: The flicker thing.

The cheaper LEDs wont cure the flicker issue, they're just as bad as flos.
There are LEDs that are suitable for high speed shooting but some of them cost as much as the 700 so probably not at real option.

Tungsten units should be fine - make sure they are not on a dimmer, this will introduce flicker.
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Old July 6th, 2012, 07:55 PM   #3
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Re: The flicker thing.

I believe that that was one of the drawbacks from the high frame rate that was reported, unfortunately
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Old July 6th, 2012, 08:41 PM   #4
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Re: The flicker thing.

definitely. nothing that wasn't expected
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Old July 7th, 2012, 05:43 PM   #5
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Re: The flicker thing.

Quote:
Originally Posted by Todd Sheridan View Post
My understanding is that the flicker goes away or is reduced if using more powerful lights (1K and over) and possibly LEDs, which have a faster refresh rate.
I will test the LED thing at some point, but using 1Ks probably isn't practical for me.

If anyone has any experiences, recommendations, etc. to share, it would be great to hear them.
The obvious way to make it go away would be to use DC power for the lighting. May be difficult if we're talking about 110/220 volt, but what about something like Dedo lights? (eg D E D O L I G H T )

The standard ones use 12/24 volt bulbs with dimmer/power supply unit - I'm not sure if those power supplies give out AC or DC, but if AC there's always the possibility of running the heads from batteries or some regulated supply.
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Old July 8th, 2012, 01:36 PM   #6
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Re: The flicker thing.

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Originally Posted by Todd Sheridan View Post
But, there is definitely a noticeable flicker when shooting at a high frame rate using any sort of practical indoor light source. And, of course, this is an issue with the high frame rate and heat fluctuations with the bulbs...
...and the interaction with the chosen frame rate and shutter speed. To avoid flicker with recording under mains frequency lights, you have to match mains frequency. The point is to recognize that the lighting is responding, at least in part, to the sine wave from mains power (60Hz in NA, 50Hz in Europe, etc.). To avoid flicker under this kind of lighting, you have to setup the camera to expose under the same part of the sine curve. Each frame. This implies a frame rate that's an even multiple of the mains frequency, and a shutter speed that's an even multiple of mains frequency. So in 60Hz land, you should be fine shooting at 60, 120, or 240fps and 1/120, 1/240, or 1/480 second.

If you still have some flicker, it could be that you're seeing either power supply ripple (fluorescent ballast), or you're just getting lucky and hitting an interesting part of the sine curve (say, the bottom) and watching the filaments cool (tungsten) -- all at different rates. This is why shooting at high frame rates under mains frequency lights isn't highly recommended. It can certainly be a crap shoot, as you have found.

In any case, it's always better to control the lighting with cine instruments if you can. A high frequency HMI or fluorescent should look like smooth continuous lighting under your maximum frame rate.

It's possible that shooting at a lesser frame rate will lessen flicker as well. It's possible that shooting at, say, 120 fps and going to 240 fps in post using, say, Twixtor, might be a reasonable compromise that gets rid of most of your flicker. IDK, just thinking out loud...
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Old July 9th, 2012, 04:08 PM   #7
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Re: The flicker thing.

Well, after doing some more research, I'm not so sure. Seems that even HMI and fluorescent cine lighting can show some flicker at frame rates above 120 fps. AbleCine's website has this about using a Phantom. See all the way at the bottom about lighting for high-speed. Might give an insight or two.

If you find things that work, please post and let the group know.
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Old July 9th, 2012, 06:10 PM   #8
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Re: The flicker thing.

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AbleCine's website has this about using a Phantom. See all the way at the bottom about lighting for high-speed. Might give an insight or two.
That implies that the flicker rate is the same as the mains frequency (50Hz or 60Hz) and that is not correct, the lamp flicker will be twice that rate - nominally 100Hz or 120Hz.

Reason being that the filament will heat up as the current increases, then cool as it drops back to zero. But that happens after a half cycle, not a whole one. In the second half of the cycle the current reverses, builds to a peak, then back to zero. Hence flickers twice per cycle, not once.
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Old July 11th, 2012, 12:21 PM   #9
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Re: The flicker thing.

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Originally Posted by Todd Sheridan View Post

Anyway, my outdoor stuff looks nice. But, there is definitely a noticeable flicker when shooting at a high frame rate using any sort of practical indoor light source. And, of course, this is an issue with the high frame rate and heat fluctuations with the bulbs, not anything that is specific to this camera. But, it's going to me an issue for me.
A friend of mine whom I'd worked with for several years did crash test photography for the auto industry. I've probed this question of flicker on many levels.

Any AC driven light-source is susceptible to flicker. It is possible to use higher wattage tungsten lights 10,000k and higher that are less susceptible to phase dimming but it never really goes away. The theory is the higher lamp temperature has thermal carryover helping to smooth over the light fluctuations. If you view the tungsten filament at high-speed you can see it change luminance levels in step with the ac phase. It is also possible to hook up 3 tungsten lights each on a separate phase to cancel out the flicker but I wouldn't guarantee it.

Xenon arc lamps. When powered by a DC source, they will be pretty much flicker-free.

You can also try HMI's in flicker free mode. Even with the flicker free mode there is still the possibility of Arc Wander, this is where the plasma arc moves within the bulb producing color shifts. If multiple HMI's are used the arc wander effect becomes unnoticeable or minimized. The use of diffusion also helps cancel out this effect, in fact I would recommend using it on all HMI light sources.

Sunlight is the most reliable flicker free Plasma light-source.
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Old July 11th, 2012, 01:56 PM   #10
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Re: The flicker thing.

You can get fluorescent lamps with high frequency ballasts operating at 30Khz or more that will give flicker free images at the frame rates the FS700 is capable of.
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Old July 12th, 2012, 01:55 PM   #11
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Re: The flicker thing.

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Originally Posted by David Heath View Post
That implies that the flicker rate is the same as the mains frequency (50Hz or 60Hz) and that is not correct, the lamp flicker will be twice that rate - nominally 100Hz or 120Hz.
No, they are talking about cine lights with high speed electronic ballasts running in the 40kHz and higher range. Much, much higher than line frequency. What they are saying is that there's more to flicker than just the ballast frequency.
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