Strobe lights synced to 60fps

[Sean Mathiesen]

Hi,

I need to Shoot a scene/plate with regular actors and VFX treated actors. 

I would like to film at 60fps and:

- use 1/2 of the frames for the Hero actors in normal lighting conditions

- use the other 1/2 the frames to capture the VFX Actors.

 I would like to sync a strobe light to the camera FPS (OFF for Hero Actors - ON for VFX Actors in {reflective Scotchlite costumes}

Questions:

1) Is there a camera system/lighting system that would deliver on this requirement?

And

2) will the flickering strobe lights disturb/annoy the actors?

[Steve Switaj]

Well, it's totally possible.

We used this interleaving technique on Super8 to fill a projection screen with
temporary material to be replaced in VFX, one frame on, one frame off.

We also did some lightning effects in the matrix sequels the same way at
72 FPS, one clean frame, a flash from the left, then a flash from the right, so
the effect could be selectively flashed in post.

In Super8 we used a Millineum at 48 FPS, and the flashes were generated
with very bright LED's. That was 10 years ago, some of the LED's we have
now are a dozen time more efficient.

The trick is you have to have some sort of controller that can look at camera
sync and gate the LED's. Film is ideal, but video will work if you have a full-frame
shutter and some way to get/use a sync signal off the shutter - as opposed to
trying to derive it from a video signal out, which has unknown delay.

Since the LED's have to turn on and off very fast, you're probably talking about
custom circuitry (that's what we did on Super8), but if you're lighting hi-gain
retroreflective suits, your lights might not need to be that huge, mostly
just a big ringlight at the camera.

The timing is tight (slop measurable in a dozen microseconds), but it's
not rocket science.

The single biggest issue is having a solid camera sync. Not all cameras are
friendly in this regard.

As far as physical effect, this is fairly distracting - think working under badly
flickering flourescents - but people will get used to it, especially if it's just
a small, lens mounted source that's not throwing much practical effect.

You may, however, trigger people with photosensitive epilepsy. It should
be noted that a lot of people who have photosensitive epilepsy *do not
know* they have photosensitive epilepsy, and this is a bad way to find out..

On one shot in the Matrix sequels we had a crew member suddenly lock
up like he was made of wood and fall right over. Scary.

That said, the ideal frequency for triggering people is 10-15 flashes/sec,
at 24FPS you're getting out of the zone, and by 30FPS you're probably
safe-ish, but put it on the call sheet anyway.

[Phil Rhodes]

Creamsource are the only manufacturer I'm aware of that have this capability. I have one of their sync boxes that I could try it with if that'd help.