Most of today’s better NLEs can simulate slow motion footage. Having said that, using your editing package is not the best way to get decent slow motion for a number of reasons. Most notably, as the software will fake the extra frames it needs from existing ones to get interpolation, and also actually re-use existing frames when necessary to “fill in the holes” it simply will not always loos that good.
Ergo, slo-mo is one of those things not-to-be-fixed-in-post but instead, best generated when actually shooting, and this, for newbies to the game, means a small tutorial in the areas of frame rate, shutter speed and ISO / lighting might be needed.
And, scary, scary, this means venturing outside the realm of “automatic” and into “manual” mode!
As you already know, video footage is made up of individual frames shot at a certain speed. Depending on where you are and how you are shooting, this is generally 24.97 or 25 frames per second (fps). This is a throwback to the early days of TV and Wikipedia has a good explanation on this if you are interested. Suffice to say in Australia, 25fps is the norm.
And while it may seem logical, to get the best out of footage shot at 25fps, you also play it back at 25fps, but of course, you can shoot at a higher frame rate and playback at a lower one, for example 50fps shoot and 25fps playback.
And hey presto, you have slow motion!
Let’s now introduce motion blur into the equation. If there was no motion blurring when shooting video, everything would look way too sharp and clear and appear unnatural and artificial. But when shooting slo-mo we need less motion blur as the images are staying on the screen for longer making it very noticeable and again, unnatural.
To do this, we need to increase the shutter speed – the amount of time the shutter is open letting light in – to compensate. Thankfully, the basic formula to do this is very easy; simply double your frame rate to get the correct shutter speed. For example, if shooting at 50 fps then your shutter speed should be 100 fps (or as close as you can depending on your camera settings).
Lighting and ISO
And this introduces the next variable, light, as increasing the shutter speed decreases the amount of light getting into the camcorder / camera. This means ideally you have to have a very well-lit area. If not, then you will need to increase the aperture of the camera (open it up) or increase the ISO setting to compensate.
And in case aperture is also something new, bear in mind the SMALLER the number, the wider (more open) it is eg f4 lets in MORE light than f16 say.
These last two cause a trade off or either footage getting blurry or grainy, so you’ll need to experiment. As with anything, practice makes perfect.
(Cover image courtesy Ross Gibb Photography)