High Speed Underwater Blue/Greenscreen
>Published : 7th May 2006
>I have an underwater commercial shoot soon mixing 5229 150fps (435ES in the pool) and 1000fps Phantom 5.1 (through portholes as there doesn't seem to be a housing available for hire). PL lenses on both cameras.
>We're shooting 10 adults of various skin tones to be beauty lit and keyed over plates. I'm undecided whether to suggest blue or greenscreen as the water is bluish which will contaminate a blue key once the skin tones are balanced and muddy a greenscreen. Thinking about suggesting shooting with a yellow filter and a luminance key.
>Lighting wise I'm putting 4K & 2.5K HydroPars and underwater Kino’s into the pool, a HydroPAR Underwater Ringlite on the 435 and smashing 18s through the surface, softening enough that the miniscule ripples disappear (the Director is shooting in water for a weightless look, the effect will be spoiled by surface beams). The 600ASA @ 25fps Phantom will become 14ASA @ 1000fps (5.25 stops), so at T2 I need 330+ foot candles. I'm all HMI to avoid flicker (I got burned with flicker from a 5K @ 150fps a few years ago, although I've been told that 10&20Ks @ 1000fps are ok..), I'll correct the 5229 with an 85b, I'll try to WB the Phantom in camera and finish the correction in post (unless it appears too noisy in the blue channel) as I'm loath to lose any more stop with filters.
>Of course, no time/budget to test, hence doing my homework.
>Any suggestions gratefully received, as ever.
London based DP
>How big is the Phantom?
>I might have a housing for it.
>Without going into the key issues which others will be a lot more expert than I, your light level is obviously a concern.
>My tendency would be to avoid HMI's altogether, partly because of flicker risk but also because you risk loosing light when the shutter speed is 1/2000th of a second. Also it seems that you don't want "stripes" of light so what you really want is a very high overall intensity made with soft light. What about space lights rigged very close to each other and just above the surface of the water? If that's not enough level, then a rig with “Wendy’s” bashing down into a big silk might be another way. Another good thing is to line the pool with white everywhere not in frame.
>If you want some tungsten lights with plenty of punch then rock and roll lights of various kinds are good...
>I have been testing 5218 with a 2 stop push and rating it between 1200 and 1600 ASA and it looks very good: not much increase in grain with a tendency to loose highlight detail, which shouldn't be a problem in your situation.
>On another note, we did weightlessness in Earth Girls Are Easy by putting trampolines under the frame line and shooting at 1000fps with the frame set at the point in the jump when the actor was changing from rising to falling...
>Sounds like an interesting shoot - Good Luck!
DP Devon UK
>I did a job a bit like this a while back, it was meant to be the interior of a washing machine so we had to avoid "caustics" as you do.
>The best solution was to put a 20 * 20 across the top of the tank and light through that, any other approach gave us caustics.
>We also used the underwater Kino's and SeaPars.
>Try and get hold of one of the really bright screens from Cirro Light.
>I'm using a green screen called Lacotta at the moment and it's amazing! Needs no lighting at all. I've used a blue version of this in the past as well.
>Removing the blue from the skin won't cause the screen a problem as it's seen through even more water and is bluer than normal to start with!!
>Geoff Boyle FBKS
Director of Photography
>Thanks very much for the advice.
>I've been informed today that the 600ASA rating for the Phantom is incorrect and that a much more accurate figure is...100ASA. Production were over the moon when I dropped that on them.
>"I might have a housing for it."
>The Phantom is here :
>but I wonder if we'll be able to get your housing across the pond in time. Or if the cables will be watertight? What do you think? If possible the Director would be over the moon.. Obviously ignore where it states the faster ASA figure. (To be fair, until I check it myself on Saturday I can't rubbish them, but the Arri Tornado is 120ASA so it sounds as if the 600ASA stated is wrong as both seem to run similar technology.)
>"My tendency would be to avoid HMI's altogether, partly because of flicker risk but also because you risk loosing light when the shutter speed is 1/2000th of a second"
>I was planning to use flicker free HMI as we'll be at 1000fps for much of the day. Have I misunderstood - why would I lose more light at 1/2000th on HMI than Tungsten? We haven't the labour to rig the spacelights, although that would be perfect for the quality of the light. Wouldn't the 1K bulbs flickers though? Same with the Wendy, the 650W would risk pulsing? I agree with you about pushing 5218, I've sat in a TK before and forgotten I'd pushed it until I saw the board, on those particular shots it looked almost identical. What camera did you use for the 1000fps shots on Earth Girls?
>"The best solution was to put a 20 * 20 across the top of the tank and light through that, any other approach gave us caustics."
>Sold, it's a plan. I was thinking of going through frames but it's simpler to make a single giant frame over the water rather than individual ones per light. I'm going for 20Ks or T24s as I'll get more on the budget than 18Ks, I won't have to waste light correcting and I'm thinking that the huge bubbles won't give me away with pulses. I had planned to put them on different phases to mix any problems, and a friend just suggested that too so I'm fairly sure it'll work. I've been advised that underwater HMIs are very reliable so better to work from above. I will have a 4ft 4bank in the water as front fill/eyelight.
>"Try and get hold of one of the really bright screens from Cirro Light."
>Great tip, I've asked Production.
>Thanks again, great advice, very much appreciated.
London based DP
>Actually I think it must have been 300fps with a Panastar as it had to be pin registered for the blue screen. I remember a lot of talk at the time about using high speeds with blue screens and how it wouldn't work etc. 1000fps with people under water will render them virtually dead still I would have thought!
>My HMI comment is more hunch than science. I expect someone more technical than me could say whether there is any truth in the matter. I do know that tungsten lights are continuous so they can't flicker no matter what you do. I just wouldn't want to risk flicker is such a delicate situation: flicker free can still flicker in some circumstances (like when it isn't working!).
>Oliver wrote :
class="style11">>...I do know that tungsten lights are continuous so they can't >flicker no >matter what you do.
>Tungsten lamps with smaller filaments can "flicker" at higher frame rates. The AC 50/60 Hz sine wave actually becomes visible, usually over 1500 fps, so that you start to see the rise and fall in the smaller filament lighting fixture. The original poster mentioned getting flicker on a 5K lamp but I have never heard of such a thing under 2500 fps.
>The smaller lamps flicker more than the larger filament lamps because the response time of the attack and decay of the sine wave is much quicker with the smaller filaments. Think of when you quickly douse a 1K Par verses a 10K on a dimmer and the response time it takes for them to go black. The 1K is much quicker and that is why the sine wave can be seen in higher frame rates.