Slow motion videos can be absolutely mesmerizing, that’s why this week in Zeferino Professional Lighting we want to get a closer look at the slow motion technique, because there’s a lot more to shooting one than just setting a higher frame rate. If you’re interested in learning more about how to shoot high speed video, The Slanted Lens provides this excellent video that breaks down the concepts and settings needed to capture one correctly.
Shutter speed & frame rate
Our brain cannot distinguish beyond 30 frames per second. By filming anything faster than that it can be put on a 30fps timeline and it will play back slower. For example, filming at 60fps is 2 times slower than real time.
The iPhone 6 shoots at 240 fps, is 8 times slower than real time. We filmed at roughly 500fps and 1000fps which is 16 and 30 times slower than real time respectively. To accomplish this without ghosting in the footage the rule is the shuter speed has to be double that of the frame rate. At 60fps you need to be shooting at 1/125th of a second, 500fps is 1/1000th of a second and 1000fps is 1/2000th.
As we found out first hand, if you’re shooting somewhere dark, you’re screwed. The faster the shutter speed, the more light you need to shine on the object.
For 1000fps with the shutter speed at 1/2000 you need a lot of light. What seems ok to the naked eye, won’t necessarily be bright enough when shooting slow motion.
It’s not as simple as turning on more lights because they can flicker. Some low quality LED panels have a pronounced flicker when footage is slowed down. You can see this example in the movies or old TV shows where a TV in the background is flickering because it’s light output is at the same or slower rate than the footage being filmed.
Depending on the camera, your audio might automatically be muted. If you’re lucky enough to get sound, depending on the speed of the footage, the audio might sound like Dory speaking whale in Finding Nemo, or a low groaning sound. This is why slow motion videos often have musical overlay.
Every one of these should be carefully considered before you jump in and start recording because each affects the other. For example, you can achieve the natural amount of motion blur by setting your shutter speed at double your frame rate, and higher frame rates and shutter speeds don’t give your sensor as much time to capture light; these results in darker images, which means you’ll need more lighting.
Motion blur and underexposure aren’t the only things to look out for when shooting slow motion, you’ll also have to pay attention to flicker, which is caused when the filament inside certain lights rapidly heat and cool. This means you’ll need to specifically choose which kind of light to use for your slow motion shots, leds are great for high-speed, as well as certain HMI and fluorescent lights.
There’s no right or wrong way to do this. Say you accidentally captured a lot of motion blur, but maybe you like that! Maybe you got a little bit of flicker from your light source, but it looks kind of cool. As long as you know about the potential issues that may arise when shooting high-speed footage, you shouldn’t have any problem preparing to get the look you want.