First gig, slow-mo, and strobing!

marlontorres

marlontorres

Well-known member

Just wrapped my first gig with the FS700, first of all... LOVE IT! Played with some slow mo of course. I do have a question though... I ran into some issues with strobing lights in the coliseum, any way to fix that? I assuming I can just find a shutter that won't strobe or is it just unavoidable because its in super slow mo?
 
If the venue has discharge type lighting you will see the discharge cycles which are completely out of sync with the frame rate of the camera. Shutter angle will not fix that - the problem is nearly as old as cinema.
There are a huge variety of lights and ways to drive them. In stadiums, they usually use some type of arc lamp that pulses faster than your eye can see, but not faster than your camera can see.

On Any Given Sunday - the DP used a massive array of 6k tungsten space lights to replace the arcs in Texas Stadium. No flicker, but spent millions getting there and you could see the lights in almost every shot.
 
That some great footage. I don't mind the flickering at all, in fact I think i'm used to it.
 
that would be a instant QC fail for broadcast tho...

i would try de-flicker filters masked to only wack the affected area's when gradeing

d
 
If its flourescent lighting in a building in North America. Being that electricity is at 60 Hz. Would you use a shutter speed at a multiple of 60 to help with this??

I am really taking a stab in the dark here and don't pretend to even know what i am talking about!!
 
It would absolutely pass QC. Watch ANY sports game on television. If they cut up more than 120 it strobes. From NFL to NHL. Strobbing slowmo is on TV every single day if you look for it. People have adjusted. Obviously avoid it when you can, but in the end your subject should steal focus.
 
marlontorres said:

Just wrapped my first gig with the FS700, first of all... LOVE IT! Played with some slow mo of course. I do have a question though... I ran into some issues with strobing lights in the coliseum, any way to fix that? I assuming I can just find a shutter that won't strobe or is it just unavoidable because its in super slow mo?
Click to expand...

Nice, really enjoyed this!

The flickering of lights can't be solved with shutter speed, the problem is in the light source frequency. To be honest, I was actually surprised how little of flicker you had. If you framed the shots to avoid having light sources in the frame, it would be impossible to spot it.
 
PremiumIC said:
It would absolutely pass QC. Watch ANY sports game on television. If they cut up more than 120 it strobes. From NFL to NHL. Strobbing slowmo is on TV every single day if you look for it. People have adjusted. Obviously avoid it when you can, but in the end your subject should steal focus.
Click to expand...

Double dare ya to send it to Deluxe LA for QC....
 
Nice footage, thanks for posting

I think you "lucked out" a bit... The arena lights are cycling almost exactly some multiple of 2x whatever settings you had it at . If you go frame by frame you will notice this. This means you can dump the even or odd frames and interpolate using optical flow techniques (e.g. twixtor, after effects, nuke, avisynth etc...) to replace the frames you dropped . You generally get decent interpolation (low artifacts) when the source footage is slo mo to begin with (there is less motion between frames, less error)

Dermot mentioned the other option, masking. You could combine the 2 by taking the "fixed" fights and doing a rough mask (top half "lights" vs. bottom half players) , you should not need delicate/tedious roto work using that approach

eg. This is was just simple interpolation to stabilize the lighting (if you look closely you can see some edge morphing artifacts on the players) , if you combine the rough mask it should be a simple quick fix

 
I think under those situations with no control over the lights you are S.O.L. But have shot in controlled situations at 240 fps and lowered the shutter speed a bit (it was not 180), and got no flickering. Not sure if that would work in an arena though.
 

I shot this at a concert...there was little flickering but I still can't figure it out why? but other shot on the street I get lots of flickering. I had 100FPS, 200FPS, I even had 400FPS.
 
You can't do anything about it in camera because it is not the camera causing it but instead the lights themselves. Perhaps this would be useful; I wrote it for the Phantom cameras but it applies here are well.

Lighting for High-Speed
Lighting issues are not specific for the Phantom cameras but for high frame rate photography in general. Even with the great sensitivity of modern cameras, be prepared to use a considerable amount of light. Beyond illumination, the largest issue in high-speed lighting is flicker. Tungsten lights actually have a flicker rate. When powered by alternating current (AC) electricity, the power cycles 50 or 60 times per second (depending on the country and its power system). During the down cycle the tungsten lamp filament can dim slightly, causing flicker. The amount of dimming is related to the type of bulb, wattage and physical size of filament. In general, we have found that lamps larger than 2000 watts use tungsten filaments so large that they do not have time to cool and dim before the power cycles back up. Therefore, we recommend using 2K or greater tungsten light fixtures when shooting above 120fps in 60hz countries and 5K or greater when shooting above 100fps in 50hz countries. Be aware that a unit such as a nine-light is NOT a large fixture but is actually an array of smaller lights and as such can flicker.
Some additional recommendations are to use DC power for tungsten lights, which eliminates flicker entirely. HMI and fluorescent lights are generally fine for speeds under 120fps as long as they use electronic ballasts. Magnetic ballasts should not be used. HMI lights can suffer from “arc wander,” whereby a plasmatic “hot spot” can move about within the bulb, causing an amorphous shifting movement in the light output. LED lights are subject to the electronic circuits driving them which can create a vast array of refresh rates, but generally we have found that LED fixtures designed for the production community will not flicker as long as they are not dimmed.
Finally, the shutter angle on the Phantom can affect flicker as well, as a greater shutter angle allows for a longer response time from the light. When shooting extremely high frame rates, it may no longer be necessary to retain a 180-degree shutter to capture the motion generally preferred for a filmic look. A 360-degree shutter allows both more light sensitivity and reduced flicker possibilities.
 
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