F55: Quick and Dirty Sample of F55 S&Q @ 240 fps-and I noticed flickering- any suggestions

captainjman

captainjman

Well-known member
Quick and Dirty Sample of F55 S&Q @ 240 fps-and I noticed flickering- any suggestions

I did a quick test on the F55 at 240fps and noticed flickering. Any advice on how to get this to stop? I noticed it a lot more under sodium street lights, it was like a strobe was going off. Here if you look at the reflections of the TV on the soda bottle for instance you can see the flicker. Any advice???

http://youtu.be/Ld6uEt2PylE

you can see the flicker at 1:08 on the diet soda bottle, it's the TV reflection - it always shows a flicker on the TV and some lights like the high pressure sodium street lights.

Any suggestions?
 
We were having problems with that as well shooting abroad and have some queries in to sony on how to deal with the different power systems and light frequencies over there versus here.

I can sometimes beat most of it by matching framerates to multiples of shutter speeds, while messing with the anti flicker stuff in the Camera menu. Theres 50/60 and Auto versions of anti flicker.

On our next trip I'm going to try putting the camera base setting of 25p instead and then It should unlock some more variables in the high FPS so I can try and loose as much flicker as possible, that MAY help...
 
Not all forms of light are actually constant, and Alternating Current (AC) works in cycles, either 50hz or 60hz depending on where in the world you are. That tends to mean 50 or 60 cycles of light per second. Now, when you shoot a camera at 60 frames per second, or a fraction there of (30fps) there's not visible flicker because you're matched to the cycle.

However, if you're out of phase with the cycle, typically by being faster than it, you'll start to see the cycles of the light.

Practically, I'd shoot under better light sources. Or try to use a frame rate multiple of 60. (120,240)
 
Digital Anarchy have a Beta of a new Flicker Free plug in you can try. It worked very well for me on a few interior shots we did in Ireland last summer that were flickering.

cheers

Morton
 
Thanks - I was shooting at 240 though - and I had turned on the 60hz and even tried the 50hz flicker option via the menus. I wonder why lights operating in the us (60hz AC street lights) would flicker so horribly. Next time I will try a different frame rate like 230, 220, 210 maybe one will stop.

And then with the water video I posted - you can see the TV flicker even though it was being used as a digital picture frame and the picture was only changing every 3 seconds the flicker you see is not because of fast action strobing effect of any kind. It's a plasma with a refresh rate of 600hz, so maybe I should try 200 instead? this is so bizarre.

I noticed that turning on the flicker setting didn't make any difference in any setting.

Jason
 
I may me mistaken, but I believe then when in S&Q your shutter speed is 1 / (S&Q speed) so in other words I think it was 1/240th when shooting S&Q240fps automatically. Can you specify a different shutter speed for this?

Jason
 
The slowest possible shutter speed during S&Q is 1 / (S&Q speed) --- sometimes that number is rounded off a little -- but you can go faster than that if you choose. For example, I shoot most of my 240 fps footage at 1/500th.
 
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I work on a crew that shoots with the Phantom, and now the Miro, we have 4 plasmas on our set that always flicker when in the high speed shots. The owner/operator of the phantom has been shooting high speed since the days of photosonics and has told us there is no solution to eliminating the flicker. Not sure of the technical reasons behind why the plasmas act this way, our only solution has been to avoid the tv's in high speed shots.
 
If you notice on the Olympics with the super slomo on the night time ski runs there is a subtle flicker. It has the same flicker cadence as four years ago. If there was a way to get rid of it in this programming, they would have done so.
 
I noticed major flickering in slo mo watching the super bowl, I said wow if it's there maybe that's the norm.
 
Keep in mind when shooting slow mo, if your time base is 23.97 or 29.97 to use absolute shutter speeds and not relative shutter angles.
 
Yes - you were right - I tried it out and was able to reduce the flicker to almost nothing.

I set the shutter speed to continuous and not step - and was able to dial in a shutter speed like 1/364, dialing in every single one until the flicker was barely noticeable at all. (i chose that number randomly, I don't recall what setting it way) -

I don't know what the real sub-field refresh rate is on the llamas, but I think it's 600+, and at 23.98 fps - I think you need some obscure number to find the right frequency

Another interesting thing that I found was that it depended when I turned to the right frequency if the screen would be brighter or dimmer. If you catch the right frequency while the plasma TV is flashing brighter, then the image stays brighter, and if you catch it while it's dimmer, it stays dimmer.

how weird is that? (I am sure if you are a physics major it's not that amazing)

Jason
 
I have been shooting a lot of phantom recently and have had to relearn what lights to use.

Here is a list of lights that WILL NOT show flicker for high frame rates:

"video" LEDs (i.e. LightPanels)- need to be at full brightness if dimmable
Plasma lights (i.e. Hive lights)
Arriflex HMI's with "high speed" ballasts (i.e. m18)
Tungsten fixtures 2K and higher

List of Lights that WILL flicker:

HMI's
Highpressue sodium (street light)
Low voltage LED's
Lower wattage Tungsten/hologen
All florescent lights

Its not the camera, its the physical limitation of the lights.
 
It's funny, I learned this stuff from the ASC manual, because back in the day that was the only way to learn it besides being on set and paying attention to the DP you were assisting.

Nowadays, if Phillip Bloom, Den Lennie, or Alister Chapman haven't blogged about it, then the info is lost to the ages and people wind up reinventing the wheel.

captainjman said:
Another interesting thing that I found was that it depended when I turned to the right frequency if the screen would be brighter or dimmer. If you catch the right frequency while the plasma TV is flashing brighter, then the image stays brighter, and if you catch it while it's dimmer, it stays dimmer.

how weird is that? (I am sure if you are a physics major it's not that amazing)
Click to expand...

It's called phase:

psc2-Adjusted.jpg
 
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In the bowels of my set bag, I have carried a light tachometer that measures the frequency a fixture is operating at. There are many factors involved, but as Nate pointed out this is cinematography 101. How light is created has a LOT to do with how it is captured.

Discharge sources include flos, HMI, etc. They are called that because they work by very quickly discharging stored energy into a very small space (the bulb) filled with something that will glow when a lot of energy runs through it. The details are best left for another day. Essentially, these sources are literally flashing lights. The are simply flashing at a rate just fast enough that our eyes perceive as a continuous light. Cameras take pictures a for a very specific amount of time at a very specific interval. If the camera is taking a picture between the flashes of the discharge lamp it will look dim. The timing of the camera and the lights are never synched together to they will come in and out of time alignment at regular intervals making them appear to flicker. This has been something that was calculated in the past when shooting film would not allow you to see your problem until the next day.

As things have advanced, various methods of driving discharge lamps have reduced or in some case eliminated these problems. Some by drastically increasing the rate of flicker from 50-60 pulses per second to many thousands of time per second. Not always perfect, but better. Stadium lighting generally uses a form of discharge lamps that follow the power line frequency of 50-60 cycles per second. Those lights tend to be the worst offenders and there is very little anyone could do about it short of re-writing the law of physics.

LED lights are way more sneaky. They are constant ON devices with positively no flicker at all whatsoever - in theory. In practice we all want to dim our lights and vary the color temp etc. LED's do not dim like a regular light bulb. They generally need to be pulsed to accomplish a lower intensity without losing color. They also require a minimum voltage to work at all. The pulsing is called Pulse Width Modulation and essentially turns the LED fully on and fully off rapidly (just like the HMI's and Florescents have always done) If PWM is ON 50% of the time and OFF for 50% of the time the LED will appear to our eyes as being half as much light as always on. That is why LED fixtures that are full on are safer than the ones that are in some state of dimming. I am careful to be very general here because everyone has a variation of how they drive LED's for motion picture use. Some are better than others at choosing the duty cycles and frequencies to operate. You have to test before you will really know.
 
captainjman said:
Thanks - I was shooting at 240 though - and I had turned on the 60hz and even tried the 50hz flicker option via the menus. I wonder why lights operating in the us (60hz AC street lights) would flicker so horribly. Next time I will try a different frame rate like 230, 220, 210 maybe one will stop.

And then with the water video I posted - you can see the TV flicker even though it was being used as a digital picture frame and the picture was only changing every 3 seconds the flicker you see is not because of fast action strobing effect of any kind. It's a plasma with a refresh rate of 600hz, so maybe I should try 200 instead? this is so bizarre.

I noticed that turning on the flicker setting didn't make any difference in any setting.

Jason
Click to expand...
Welcome to the world of high speed/slow mo

Power is generally delivered in AC, where the current fluctuates quickly between a positive and negative voltage (it allows you to double the charge with the same voltage). In NTSC world, the fluctuation happens at 60 Hz, or 60 times a second, in PAL land it happens at 50 Hz, or 50 times a second.

Each full cycle will have four phases, from zero to +ve, +ve to zero, zero to -ve and then -ve back to zero, the power will therefore pass through zero voltage twice.... so if a light is attached directly to the power source (e.g your bog standard incandescent light bulb), the light will very quickly phase on and off.

If you're shooting at 60 frames per second, then you will not notice any fluctuation, the frames last the same duration as a complete power cycle. At 120 fps each frame will last half a cycle and so will cover 2 phases, so again you will get away without seeing any fluctuation. However at 240 fps, each frame will last the same amount of time as one phase, you're going to see flickering on play back.

The best option is to either use flicker free ballasts on your lights, or use the big bright thing in the sky... if neither of those is an option, then either reduce to 100 fps or fix it in post.
 
Thanks everyone - I knew most of the physics but for some reason I didn't apply my knowledge. I am a noob so thats my reason... note, I didn't say excuse, there are no excuses in life.

Anyway I was determines to cancel out the flicker in camera not in post - and was able to shoot every light source and plasma TV without flicker. I don't know why I didn't think I could change the shutter speed. I turned off the step - and put it on continuous and went 1 click at a time until the flicker was gone on each one. It shows up in the viewfinder right way.

I am going to try the NLE solution also - I have some footage I almost threw way because it was flickering like crazy.

seriously, thank you - all of you - for taking the time to teach me some basics - I realize this is cine 101 type of thing - so thanks for being my teachers today :)

Jason
 
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