The understanding of frame rates and how they pertain to filming is basic in firstly being able to record footage at the appropriate speed (ie. normal/slow motion etc..) for your film, and secondly in ensuring you expose your film correctly much like you already do for your stills.
So many people showing me clips they had filmed on their lovely new mirrorless cameras were disappointed to see jumpy disjointed or laggy footage and could not understand why they were getting better slo-mo on their iPhones than their ££££’s cameras… allow me to explain…
To understand what we mean when talking frame rates we need to understand the concept of filming movement.
I’m sure most of you already know that video/film is a series of still images which when played back at speed create the illusion of movement… much like those cartoon flick books I’m sure you have all seen or even made when you were kids.
Now.. the rates at which that movement is firstly captured at and then played back at both play a role in how that movement is perceived by our eyes.
For a “normal” rate of movement ie. how we perceive normal (not slowed down or sped up) movement through our own eyes we need need film/video to be both played back to us and captured at a rate of anything between 24 to 30 frames per second (fps)
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Understand that when thinking about frame rates, that there are 2 frame rates you need to consider..
The Project Frame Rate
ie. what is the frame rate of your project timeline.. or in other words, at what frame rate do you intend to play back your film..?
The Shooting Frame Rate
which as the title sort of intimates ..what frame rate are you going to film at..?
The project frame rate, once set, is unchangeable... BUT… the shooting frame rate can be changed depending on what it is you want to shoot and how you want that to be played back and seen by your audience… normal speed.? slow motion..? or sped up..?
Project frame rates are usually either 24 or 30 fps if you are in the US or 25fps if you are in Europe or a lot of the rest of the world.
Small aside: why 24/30 fps in the USA and 25 fps in Europe and many other parts of the world..?
to cut a long story short and without getting in to too many details that I only barely understand myself… it basically has to do with the electricity frequency in each part of the world.. in the USA the power standard is at 60hz and in Europe it’s at 50hz therefore frame rates of 30 in the US and 25 in Europe can synchronize more easily without creating flicker in the image.. NOTE that this is only noticeable though if you will be filming inside under electric lights or if you might have a tv playing in your shot. For those of us purely shooting outside under natural light there is zero effect.!
Whilst filming frame rates can vary from 24 to 240 fps (or even more on some cameras.!) depending on whether you want to film something at a normal speed or if you want to slow something down.. one rule to observe here is that for even and flicker free playback – always choose to film in a multiple of your timeline frame rate.. ie.:
If timeline is 24 fps.. shoot at 24/48/96 etc..fps
If timeline is 30 fps.. shoot at 30/60/120 etc..fps
If timeline is 25 fps.. shoot at 25/50/100 etc..fps
..so a “talking head” piece to camera would be shot at “normal” speed (be that 24/30 or 25 fps) and a slow motion bird in flight shot may be filmed at 120 or 100fps again dependent on what your base or project frame rate is.
How does increasing shooting frame rate create slow motion..?
Assume we have a timeline/playback speed of 25 fps.. every second of playback means 25 frames or images have been projected to the viewer… if we shoot at 100fps instead of the “normal” 25fps we are recording 4 times as much information and then squeezing it into the same single second of projection.. this creates the illusion of slowing down motion.
Likewise in the old black and white silent films you’d see Harold Lloyd or Charlie Chaplin be very jerky in their movements.. here the opposite was true.. their motion appears sped up and that is because every second of projection has fewer than the 25 frames (images) per second meaning that in the single second it took for Charlie to tip his hat that range of movement was recorded in only 15 images meaning there is a bigger jump in movement between images than if the same action had been recorded by 25 images.. conversely creating the illusion of faster movement.
But why the jumpy jerky footage ? What am I doing wrong..?
In most modern cameras that also shoot video we have one method of controlling “speed” and that is with our shutter speed setting.. the higher the speed, the more we are able to “freeze” the action, and as wildlife photographers this is where we are coming from most of the time. We have our cameras set to freeze a bird in flight with the highest possible shutter speed we can get away with.. and then we switch to video and carry on filming now at a shutter speed of 1/2000s
Imagine that set of images as they are projected after shooting them at 1/2000s… the progressive movement of the bird from one pic to the next in the series is so tiny and without the slightest bit of blur that the result is a staccato movement when played back at normal speed. Slow that shutter down now and you get the slightest blur in those wings which now when played back at normal speed blend together, one image into the next, creating an illusion of smooth movement.
So now that we understand a little about frame rates both playback and shooting.. how does that affect the settings we use on our cameras .?
Thankfully, there is a standard rule to make our lives a little easier when it comes to our camera settings.. and that is:
Always set your camera’s shutter speed to twice (or as close as possible to twice) your chosen frame rate… so:
if we are shooting a talking head piece to camera at “normal” speed on a 25fps timeline : we would set our camera’s shutter speed to 1/50s
if we are shooting a bird in flight that we want to slow down the action for we need to shoot a high frame rate (eg 100 fps) so we would set our camera’s shutter speed to 1/200s
This is a hard and fast rule that you need to get right in camera as fixing it after the fact is next to impossible.
To get a correct exposure we would then have to adjust our aperture and our ISO accordingly but our shutter speed must remain locked at that speed governed only by our chosen recording frame rate.
We will also in all liklihood need other methods to control our exposure because being forced to shoot at f16 because our shutter is so reduced will not give us that nice bokeh we want in our shots. And that’s where ND filters and variable ND filters come to the rescue.!
NB. Some of the newer cameras allow us to avoid having to remember this shutter speed rule by allowing us to use something called Camera Angle instead of shutter speed. If your camera allows this, set it to 180° and forget about it..!!
And that’s about it.! Let me know if I have confused you even more and if you’d like anything clarified.. I will make a video to go along with this post so look out for that link or subscribe to my YouTube channel here to be notified of future videos and when that one might drop.
all the best to you and I hope you have found some value in this article.