Understanding Frame Rates. Video tutorial. How to slow footage down.
“Did we shoot that in slow-mo?!?”
There’s no denying it. Sport looks cooler when its shot in badass slow motion. So here’s the deal and what you need to know about shooting your slow motion shots.
Firstly- unfortunately when it come to slow motion you get what you pay for with cameras. You want badass slow-mo shots in HD or ultra HD, youre going to be paying £/$10k’s for the gear. Soooooo, I pulled out my RED Gemini and grabbed my water proof JayBird headphones for some demo shots. Its worth saying that GoPro’s and DJI’s are designed specifically to shoot at high frame rates. So its worth reading this if you have one of those too.
Secondly I need you to understand this, for the sake of this demonstration I kept the shutter angle at 180 degrees, which means that the shutter speed is always TWICE the FPS. So, if im shooting 25 FPS then the shutter is 1/50, 50 FPS the shutter is 1/100 & so on. This means they all have the same motion blur. The only thing that ive changed is the direction of the footage to play it back forwards and in reverse for each FPS.
Ill be honest with you, its fine not to understand exactly why we do this, but know that we do this. THE REASON- is to create accurate to real life motion blur when playing the footage back. I’ve also decided to not change the exposure on the camera at all other than using the shutter angle because I need you to understand that ultimately IF YOU WANT TO SHOOT IN SLOW MOTION YOU WILL NEED MORE LIGHT. As you can see the shots at 225 FPS are darker than the shots at 25 FPS. This is because the shutter at 225 FPS is 1/450 and the shutter at 25 FPS is 1/50.
So lets keep this simple and use some hard and fast rules:
If you want to shoot slow-motion crank up the FPS and make sure there’s enough light. (GoPro/DJI will likely auto shutter, so you’ll just get dark footage if you shoot a slow-motion back flip at sunset for instance).
DO NOT shoot interviews at high frame rates. The best thing you can do is shoot to purpose- so interviews shoot naturally at 25 FPS (if you’re US based you might shoot 23.9 or 24 FPS). Shooting an interview or piece to camera at high frame rates no only wastes card space but also can mess up your audio sync.
If you shoot something in slow motion and play it back in your timeline at normal speed that it perfectly fine but you will end up with a ‘hyper realised look’. Which means there won’t be much motion blur and the footage could look ‘choppy’. You can flirt with this at 48/50 FPS, I wouldn’t go much higher than that.
You can speed EVERYTHING up but NOT SLOW EVERYTHING DOWN. So important to remember that you have to crank the FPS on the camera if you want a shot in slow motion.
Never slow the footage down beyond your base rate… So, if im shooting at 25 FPS base rate, and set my camera to 100 FPS and shutter to 1/200 then when I put it in my timeline/sequence I can only slow this down to 25%. Any slower and it becomes choppy, this is not a good look and always noticeable in footage.
But remember that for every rule there’s and exception…. videography just isn’t that simple. For instance, if you want to try something called ‘Locked on Stabilisation’ a very cool effect that ill do another blog post on, then youre actually going to have to shoot at a much higher shutter speed to the the FPS. For instance for normal playback, 25 FPS you should shoot at a 1/200+ shutter, this is called narrowing the shutter angle. (I know all this is mental and hard to follow). The reason is so that when you come to analyse each frame for the motion you want to make sure each individual frame is sharp and without motion blur.
Get practising with slow motion and let me know how you get one. Any questions hit me up on Instagram @MaxWilko
Max