Avalanches were crucial to our story. After studying lots of videos of real avalanches we started testing. I first built a conveyor belt and moved blocks of Styrofoam through the shot with a slow shutter speed. The blur worked but it didn't work unless every block moved a little each shot or during the shot. Animating large groups of blocks of snow would be very time consuming, so we started shooting high speed instead.
We shot in sunlight to get enough light and depth of field. We wanted a late afternoon look to match with our other footage. Cross-light from a higher angle early afternoon sun worked quite well. We were limited to where the set could be located in the yard with a lower sun and by evening fogs that often came in.
I borrowed a 16 mm Lo Cam camera that would go to 500 FPS. Baking soda flowed quite well at 400 FPS down our larger set pieces like the lighter avalanche snow we saw in the extreme snow boarding videos.
For closer shots, we used Styrofoam pieces in sizes from dust up to about 2 inches in diameter. Each block was chipped out of large Styrofoam blocks and the edges slightly rounded. We eliminated all flat surfaces and sharp corners that would look like Styrofoam. Styrofoam, because it is very light flows downhill much slower than anything heavier and 90 FPS is fast enough to record as a full-scale image. We had tried salt of different sizes, but the Styrofoam worked best. Mixing heavy and light materials didn't work at all. (Read the ASC Manual about shooting miniatures at high speed.)
We had considered tank shots with water slowing the falling material. I have done tank shots before and knew the problems. It would have probably worked but we rejected it as a too ambitious without knowing for sure that it would work for all of the different shots that we needed. The sets would have been very small scale and waterproof.
Ross built a snow chute that we dumped about 50 gallons of Styrofoam pieces through each take. Flying pieces of Styrofoam dust made a real mess, but it looked great. I suggest that you do a lot of testing by eye and with a video camera before shooting film. Make sure that your rigs work smoothly and that timing of camera getting up to speed and release of material is well planned to avoid wasting film. We wasted time fighting with a sticky gate that released the mass of Styrofoam. The sun was moving and we didn't have time to fix it that day. Good preparation is key. (See High Speed Photography in Professional Operating Techniques.)
We shot some baking soda on blue screen to matt over wide shots of the kids boarding just ahead of the avalanche. We found some Formica saturated blue enough to pull a good matte. A painted surface would be hard to clean after each take. There was no way that we could animate realistic snow moving behind stop motion puppets. This set was a teeter totter that let gravity move the powder when it reached a critical angle of steepness.
© Copyright 2004 Ron Dexter. All Rights Reserved.