What You Need To Know To Shoot Cinematic Slow Motion
By Kevin Graham
In the video world, one of the coolest effects out there is the use of slow motion footage.
And the great part about it is that most modern video cameras have at least some slow motion capabilities.
Today, we’re going to dive into what slow-motion footage actually is, how to achieve it, and when to use it.
What Is Slow Motion Footage?
Video is simply a continuous collection of stills, usually 24 or 30 of them per second, to be exact. These frame rates re-create the speed and motion blur of an image that our eyes would perceive if we were seeing it in real life, with 24 FPS being the most natural and therefore the most common.
Most movies are filmed in 24 FPS for this exact reason – it is the most “realistic” and has evolved to become a trademark element of what makes something look “cinematic”.
Slow motion footage is footage that is shot at a higher frame rate than the frame rate than you want it to be viewed at, which is then slowed down on your timeline to achieve the desired result, without stretching frames.
There is no rule in terms of how many frames you shoot, but common high frame rates include 48, 60, and 120.
How Can I Shoot Slow Motion?
If you simply shoot at 24 FPS and then want to slow that shot down for effect, there’s going to be a problem!
Since only 24 frames per second were captured, you would be stretching the video to the point of seeing less frames per second, which means each individual frame remains on screen for longer. This results in a choppy, undesirable look.
So again, if you plan on slowing a shot down, you need to film at a higher frame rate than you plan on editing in. For example, if you know your project is going to be at a frame rate of 24, and you want to slow the footage down to half speed, you should film at 48. Then, in the edit, you can stretch the footage out until there are 24 frames per second instead of 48, and you have a smooth, slow motion shot.
Some cameras even do this for you, by allowing you to set a project and sensor frame rate. This means that the footage is automatically stretched and plays back in slow-mo.
If you want a more dramatic slow motion effect, you can shoot at even higher frame rates. Some specialized cameras can shoot frame rates into the thousands.
Some things to consider when shooting slow motion are the increased effects of your light sources in your shots. The higher your frame rate is, the less light will be captured in each one by your camera’s sensor, so you’ll need to plan on this before shooting.
High frame rates can also lead to the dreaded flickering effect, caused by lights in your shot running on an electrical frequency that clashes with your frame rate. This can be solved a couple of ways: either change your frame rate, change your shutter speed, or as a last resort, use a plug-in or overlay in post to eliminate the flicker.
A quick way to eliminate flicker in post is to duplicate your shot overtop of itself, set the top one to 50% opacity, and nudge it forward by 1 frame. This ensures that the shot remains constantly lit. However, this technique does not work as well if there is a lot of motion in the shot.
When Should I Use Slow Motion?
First and foremost, slow motion is a great way to just showcase something cool happening. Whether it’s a bullet hitting a watermelon, a surfer catching a wave, or a hummingbird flapping its wings, slow motion can allow a viewer to see details in something that their eyes simply cannot capture in real life.
Perhaps the most practical and common use of slow motion is to just add an ethereal, smooth quality to B Roll. Just about anything looks cool when slowed down to half speed; even slowing a shot down just a little can result in a cinematic, dreamy look.
And on a practical level, if you’re filming handheld from a helicopter, for example, slow motion helps reduce camera shake and makes it easier to stabilize your footage in the edit.
On the flip side, you can also purposefully shoot at a high frame rate and not slow the footage down. This is a similar effect as shooting at a higher shutter speed, in that it results in a more crisp image and less motion blur. This is an unnatural look, but can be used for dramatic effect in fast-paced scenes.
Slow motion is also a great way to add emphasis to an important moment or scene in your story. It really allows the viewer to focus on what’s happening, and lets them know, “Hey, pay attention here!”.
Because the technique is so versatile and also so readily accessible, the ability to shoot slow motion is a key skill that every video creator should have.
Kevin is the Music Director and Lead Composer at Filmpac.