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Tuesday, December 14, 2010
Phantom Adventures: 1000fps on a Budget
Art Adams | 12/14
A $250,000 camera, 60,000w of tungsten lighting, 1000fps, kids, animals… what could go wrong? Not much, as it turns out.
A while back I wrote this article about some high speed tests I did in preparation for an upcoming regional spot. The results convinced the client, Rambus, that the extra expense of shooting their upcoming spots at 1000fps was well worth it.
Rambus creates technology, literally, and their inventions live in a number of everyday items that we take for granted: digital projectors, laptop and desktop computers, and video game consoles. The goal of these spots was to show how these products are used in daily life. And since daily life isn’t always that interesting, director Jono Schaferkotter, of production company Compass Rose Media, opted to show reality from a different perspective to make the mundane more exciting.
While I’d tested the Phantom HD Gold I’d not done any actual work with it, so I called some friends and colleagues and asked their advice. I’d heard, for example, that shooting faster than a few hundred frames per second could be problematic when using small lights (anything less than a 5k) on AC power because the smaller filaments dim between cycles and cause flicker. I wanted to use Maxibrutes—inexpensive units that consist of an array of nine or twelve tungsten par lights—because they put out a tremendous amount of light for the price, but as the individual lamps were small (1k-1.2k) I had to figure out how to power them with DC current.
First I did some calculations. Starting with the formula T2.8 = 100fc @ ISO 100 (with a 180 degree shutter) and working with an ISO of 250 as recommended by the rental house (Chater Camera), I found I needed nearly 2000fc of light just to shoot at T2…and that was if I left the shutter completely off! I’d never lit anything so brightly so I quickly looked up the photometrics of a Maxibrute with MFL (medium flood) lamps and discovered that by using a couple of Maxis through diffusion I could guarantee reaching that level of illumination
It’s not easy to watch a monitor surrounded by 2000fc of light!
Next I had to figure out how to power them with DC current. DC current doesn’t alternate, so the lamp filaments don’t dim between cycles as there are no cycles. The lights just stay on. The disadvantage of DC current is that it doesn’t travel very far, so line loss can be a problem over long runs. That’s why our electrical grid uses AC power instead of DC.
It turns out that most generators offer a rectified DC option, so the next question was whether rectified DC was good enough. Some people I spoke to said not to trust rectified DC at 1000fps so I discussed the situation with a local DIT who’d just worked on a Phantom shoot with Maxibrutes and a rectified DC genny. He said they’d had no problems at all, so we made sure to order the same generator.
Another budgetary issue raised its head when we discussed post options. The Phantom records to a very expensive Flash memory mag, and it’s normal to shoot during the morning with one mag and then dump it to a hard drive in the afternoon while using the second mag. (While the Phantom records 16gb of data at a time, it takes about a gigabyte a minute to transfer to a hard drive for post processing.) In post the raw data has to be deBayered and color graded, and our budget didn’t really allow for that. So we opted to use an alternate method: we recorded the HD-SDI monitor output to a Ki Pro deck in ProRes 422HQ. This method doesn’t offer the same kind of latitude that raw does, and the paint controls are simply what’s available in the monitor output menu (which isn’t much!), but under controlled circumstances this procedure works quite well.
So, knowing that I could use my favorite brute lights and work at 1000fps with enough control to expose the image within the limited Rec 709 monitor output range, I proceeded to lay out a cunning plan. And it worked. I suspect you want proof, so here it is:
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