First, some background…
High-speed cinematography (slow motion) works by exposing images anywhere higher than 24 frames per second and playing them at normal speed. The excess frames fill in the gaps making things appear much slower than normal.
Until recently, high-speed cinematography was only for large-scale, big budget productions. To shoot high-speed you needed specialized cameras and lighting, very expensive equipment.
Film cameras have been used for high-speed shooting for decades. In the industry it’s called “over-cranking” because the film runs through the camera at higher than 24 fps. Every second much more film than normal is used and more film means more film stock, more processing, and much higher costs.
High-speed video cameras have existed for quite a while but mainly for scientific and military applications such as ballistics testing.
Then came the RED camera…
Finally a tool the average filmmaker could access, one capable of photographing at higher than normal frame rates. The RED ONE could do 120 fps and the RED Epic can do up to 300 fps. There have been other cameras targeted at the film and television industry (like the Phantom designed by Vision Research) that do amazing high-speed but are highly specialized and rarer than RED cameras.
Since the introduction of the RED camera, high-speed cinematography is becoming more common in smaller film projects. Everyday I see low budget music videos, commercials and films incorporating this aesthetic into their visual storytelling.
I am asked more and more to use this technique in my projects, and I understand why. Everything looks good in slow motion! You could be standing totally still on a white background staring off into space and when shot at 160 fps and played back at normal speed, it looks weird and hilarious and amazing for some reason. It’s unnatural, so we find it strange and uncomfortable and amusing. We never get to see the world that way and it’s mesmerizing.
I have more than a dozen slow-motion shoots under my belt so I thought I would share some things to remember when shooting high-speed cinematography.
Multiples of 24
As we all know, to achieve the desired cinematic look with digital technology, we need to shoot at the magical 24 fps. We also know that film cameras expose at 1/49th but we call this a 180-degree shutter. If we keep the shutter at 180 degrees relative to the sensor frame rate, we will achieve our “film look” even at higher frame rates.
Light, Light and More Light
Lighting is always important but with high-speed cinematography, the quantity of light is paramount. The higher the frame rate, the higher the shutter needs to be in order to maintain our 180-degree rule.
Here is an example: Lets say we want to shoot at 240 fps. If we are going to keep the shutter at 180 relative to the sensorframe rate, we need ten times the light because the shutter is moving at ten times the speed. That’s a lot of light so you need to plan accordingly. Shooting outside is a good option as the sun provides plenty of light.
Flicker vs. Flicker Free
If you aren’t shooting outside, plan on using a studio. You will need plenty of electricity and room to set up lights large enough to pump out the light you need.
However, not all lights will work.
Many commercial and residential lights flicker at a very high rate to conserve electricity. This flicker is faster than the human eye can perceive so we see it as constant light. This is called persistence of image, the of a second. Don’t worry about the specifics, same thing that lets us see images in a movie theatre. When we shoot at a higher than normal frame rate, we might actually capture the light fixtures in between cycles when they are off. This creates what’s known as “rolling shutter,” usually appearing as a band or bar across the frame.
How do we prevent this from happening?
Flicker-free lights are specially designed to flicker so fast that the flicker can’t be caught on camera, or to flicker at an ultra-fast but predictable rate so the camera can be calibrated to avoid rolling shutter. An inexpensive and common source of flicker-free lighting is tungsten lights. These are run-of-the-mill lights that every filmmaker will use during their career. However, they get very hot and need a lot of power, and because you need many for proper exposure, you could overheat your subject or blow a breaker.
Sometimes I use Kino Flo lights, rated flicker free up to 300 fps or more, but sometimes you still get some flickering depending on the electricity in the building (older buildings have more flicker as the power surges). Kino Flos are nice soft sources but aren’t bright so you need many and usually close to the subject. Another option is HMI’s but be sure to get the ones with flicker-free ballasts.
Data, Data and More Data
Don’t forget that shooting at increased frame rate means using up data on your cards that much faster. Shooting at ten times the normal frame rate consumes ten times the card and hard drive space and will take ten times longer to transcode and import into your editing software. Be conservative and spare every frame. Alternatively, you are increasing your footage tenfold so one minute of high speed cinematography turns into 10 minutes so you get more footage out of it….
Make sure you do a few tests with your equipment before the big day. Shooting high speed can be expensive, time-consuming and technically advanced. Test your lights and camera before you rent the studio and hire talent. There’s nothing worse than finding out you don’t have enough lights or even worse, your lights flicker when shooting at high speed.