The best cameras for shooting 4K @ 120fps video
Which cameras can shoot 4K video at 120fps? From interchangeable lens cameras like the Canon EOS R5 to smartphones like the Samsung Galaxy S20 Ultra to 360 VR options from Kandao, we’ve rounded up the best consumer cameras for 4K 120p footage to help with your filmmaking.
But first, let’s take a look at why you would want to shoot 4K at higher frame rates.
Why shoot video at high frame rates?
In recent years many photographers and filmmakers have sought out cameras that shoot 4K video at 60fps. As technology has advanced, some are now seeking out cameras that shoot 4K at 120fps. Why do people want these higher frame rates?
Let’s begin first by examining the benefits of shooting 4K at 60fps. Shooting at 60fps simply gives you the ability to slow down footage to half speed so you can get that scene-setting slow-motion effect.
You can also output that footage at 29.7fps, which is the standard playback frame rate. This way, 60fps footage can easily be mixed with 29.7fps footage. But while it can, and is commonly, it’s not ideal and we’ll tackle that in a bit.
Starting with the obvious benefits. Footage shot at 60fps that is slowed to 29.7fps enables you to stretch 1 second of footage over 2 seconds. This is perfect for the visual effect of scene-setting. Think Reservoir Dogs.
If you try the same with footage shot at 30fps and slow it down to half speed, then you have to stretch 29.7 frames over 2 seconds – essentially 15 frames per second. That’s not enough, especially at 4K, so you end up with everything looking kind of staccato – to borrow a musical term.
Using this line of thought you’d think that always filming at 60fps would be a good idea, as you can halve its playback speed and mix it with standard 29.7fps footage as needed. However, shooting at 60fps all the time is far from ideal.
Before we go into why, it’s worth pointing out that you should always film at the frame rate you need. If the footage you’re shooting is going to played back at a standard 29.7fps then film at that standard fps. If you want slow motion, then increase the fps to cover the number of frames that you need.
For normal playback at 29.7fps, half-speed you will need 60fps, quarter speed you’ll need 120fps etc. Now we begin to understand why you would film 4K at 120fps.
Using the 180-degree shutter rule
Let’s move on to why you shouldn’t always film at 60fps – even though looking at the basics it would seem sensible.
This is where the technical aspect comes in. You need to think about the 180-degree shutter rule. This dictates that the fps should always be half of the shutter speed. At 29.7fps it’s relatively easy to find a balance of gain (ISO) and IRIS (Aperture) to enable that all-important 1/60th shutter speed.
But, crank that to 60fps and you suddenly need a shutter speed of 1/120th – and that’s quite a jump.
Shooting a frame at 1/120th of second is going to eliminate any motion blur, whereas shooting at 1/60th will give motion blur in the frame. Motion blur is important for video as it helps with that all-important persistence of vision. The blur actually helps with smoothness of playback.
That 4K footage shot at 60fps and 1/120th of a second played back at 60fps will look fine. There’s enough content there for the motion to look silky smooth. Stretch that footage out over 2 seconds and the optical illusion and lack of blur still fools the eye, but, reduce it to 30fps, and you start to break the 180-dgree shutter rule.
The effect is admittedly slight, but it is noticeable. Break the 180-degree shutter rule with faster shutter speeds and you get the action-packed 300 gladiator-style look. Slow it right down and it all becomes a bit romantic.
Ultimately 60fps is a sought-after feature as it enables you to shoot smooth slow motion, and these days it’s an effect that you as a filmmaker can’t be without, but do be careful as using it wrongly can have a dramatic effect.
Why shoot 4K at 120fps
Recording at 4K at 120fps is pretty niche, but it’s still a fantastic feature to have in a camera.
There are a few points to take into consideration when looking at a camera that shoots 4K at 120fps, such as the amount of data recorded. This is usually measured as 100mb/s (megabits per second) rather than 100mb per frame.
Most cameras, especially mirrorless and DSLR, will therefore split the bit rate across frames as vbr (variable bit rate). If the bit rate was fixed, then at 30fps 100mb/s, each frame would be 3.3Mbs.
Crank it to 60fps and that drops to 1.6Mbs.
This isn’t the way it works due to vbr. The more frames you have, the less change you have between frames and the less data needs recording.
So one frame may max out at 3.3mbs where there’s tonnes of movement, and the next may be 1mbs where there’s less change in the frame.
Shoot at 30fps and the likelihood is that more will change within the frame so the data recorded will be greater.
Still, as the frame rate increases even with that flexibility of variable bitrate, it can still push the limits of the camera’s max 100mb/s.
Take the GoPro as an example. You’d be hard pushed to see the difference in 1080p action footage shot at 30 or 60fps, but push it to 120fps and you start to see some pixelation. At 240fps you really start to see the drop.
Use the same settings for a static scene and the quality of the high fps footage will still look good. Less has changed in the frame so less data needs to be recorded.
Likewise you’ll often see cameras such as the Canon EOS 5D Mark IV that will record 1080p at 60fps, but you need to drop the resolution to 720p to record at 120fps.
It’s probably limited by Canon as the 4K mb/s is 500mb/s, which seems insanely high.
4K at 120fps is amazing, but can the camera actually cope? What’s the mb/s at 4K? Is there enough scope to capture decent footage?
The Sony RXO can shoot at 1000fps in 1080p, for instance, which seems impressive until you see the quality of the footage in normal lighting conditions.
Then there’s the heat issue. All that processing can come at a price.
Finally, there’s shutter speed. Shooting 4K at 120fps, the shutter speed needs to be set at 1/250th of a second (there’s no 1/240th so you round to closest).
That’s all well and good but then lighting really becomes an issue.
You also need to consider file size and processing power. 4K already consumes storage, but slow-motion footage requires rendering and processing. This is where you really need to start looking at Nvme M.2 hard drives.