Today we're talking about motion blur, shutter speed,
and if the 180° rule should be respected if delivering
at frame rates higher than 24p.
Let's get undone!
[offbeat music]
♪ Gerald Undone ♪
♪ He's crazy ♪
What's happening, everybody? I'm Gerald Undone
"and the Mitochondria is the powerhouse of the cell."
So, I was asked to tackle this topic by a gentleman
named Philipp on Twitter who had made a video
about the 180° rule on YouTube that seemed to stir up
some controversy and misconceptions.
And he wanted me to try and create a test
to demonstrate it for him.
In his video, he talked about how the rule originates
in rotary disc shutters from older cameras
that aren't really used today and thus he felt that the rule
needn't be strictly followed, especially when shooting
at higher frame rates.
For those that don't know those old rotary discs
when set to 180° would essentially have half a circle
or 180° of a spinning disc open
and 180° closed to only allow the film to be exposed
for about 50% of the time.
On modern cameras we try to emulate this effect
by setting our shutter speed to as close to that ratio
as possible, by doubling our frame rate and using that
as our denominator in the shutter speed fraction.
So 24p would be 1 over 48 or 1/50th of a second
shutter speed. Philipp's stance was that
if you're always respecting the 180° rule,
then at 120 frames per second, you'll have a 1/250th
of a second shutter speed and therefore you'll have
insufficient motion blur.
Conversely the most common argument in support
of the 180° rule, even at higher frame rates,
is that the relationship between the frame rate
and the shutter speed should remain constant
to keep the effect of that relationship consistent
in your videos.
So, I've made this little test setup here
using a drill and a ruler. I'm able to spin this
at just over one second for a full rotation
and then shoot it at different frame rates and shutter speeds.
This gives me a controlled look at motion blur
for each combination.
It does accelerate a bit on the down swing,
but that too remains consistent
so, it doesn't affect our measurements.
So let's go over these clips together
and discuss the results, but there are a few questions
I want to try and answer with this test.
One, when it comes to motion blur,
is shutter speed the only thing that matters
and will the amount of blur remain the same,
even when changing frame rates
as long as the shutter speed is the same.
Two, should you use the 180° rule
for frame rates higher than 24p?
Three, what has the biggest impact
on the feel of a video and that soap opera effect
we associate with higher frame rates?
Is it the fact that there are more frames
or that the shutter speed is higher?
And finally, four, which combination looks most natural.
For that last point, I've recruited
some of my nerdy internet friends
to give their opinions on the tests as well
so that we can get some different perspectives
on what looks best to different eyes.
Alright, so let's start with question number one.
What affects motion blur?
Going through the shots I can tell you that it doesn't matter
the frame rate. The amount of blur is determined
by the shutter speed alone. We can see this by just pausing
the ruler in the same position and gauging how thick it looks
or how long the trails are.
It doesn't matter if we shoot
at 24 frames per second at 1/50th
or 60 frames per second at 1/50th,
the ruler looks the same. And it also doesn't matter
what the project frame rate is either.
This video is being uploaded at 24 frames per second to YouTube
so, I can't really show you true 60 fps,
but I compared the 60p footage in a 60p timeline
on my computer and the results were the same
as the 24p timeline for motion blur,
as long as the shutter speed was the same.
And this observation is likely what inspired Philipp
to make his video, and which brings us
to question number two: knowing this,
should we still use the 180° rule for higher frame rates?
For that, it depends on how you're delivering the content.
If you're shooting 60p or 120p with the intention
of slowing it down in post to fit a slower timeline like 24p,
then yes, you should absolutely still respect the 180° rule.
It's true that the motion blur will be reduced,
because the shutter speeds will be much higher.
Here have a look at what 1/250th of a shutter looks like
compared to 1/50th. You can see that if you followed
the 180° rule for 120p, you'll get much less motion blur,
but the reason why this looks natural is because
when slowed down the object is moving
at a much slower rate so your eyes expect less motion blur.
If you kept the 1/50th of a second shutter,
it would be way too blurry for a ruler spinning that slowly.
So that's why we should keep the 180° rule
for slow motion footage to maintain
that speed to blur relationship.
However, that also means the opposite is true
if you're not slowing down your footage.
So, say you're shooting at 60p and you're either
delivering in 60p, or you plan to just put it in a 24p timeline
and drop frames. In either of those cases,
you should use a slower than 180° shutter
like 1/50th or 1/60th, because you aren't slowing down,
so your motion blur shouldn't be reduced.
Ideally to make it the most consistent with your 24p work,
you would use a 1/50th of a second shutter,
but some cameras won't allow you to choose a shutter speed
lower than your frame rate because it can cause judder.
So in that case, just use 1/60th.
The difference in a 1/3rd of a stop is minimal,
which we can see here by comparing the two.
The 1/60th shot is only slightly thicker
with slightly longer trails. Not enough to really make
a huge difference and only noticeable
when comparing side by side.
For fun, here's some different photos
at different shutter speeds to give you an idea
of how much shutter speed affects motion blur.
So, if moving from 1/50th to 1/60th of a second shutter
doesn't change the shot that much,
why does 30p look so much different than 24p?
It can't be the motion blur, it must be the frame rate.
Which brings us to question number three,
what causes the soap opera effect
and can you minimize it with slower shutter speeds?
For this question and question number four
about which looks the most natural,
I've enlisted the help of some of my fellow YouTube nerds
because I can't actually show you different frame rates
in a single video. But if you look in the description,
I have included a link to a video that shows 60p footage
on a 60p timeline at a few different shutter speeds
for you to evaluate the differences. But if I were
to give you my opinion, I'd say that the biggest impact
to a video feeling filmic and natural to me is the frame rate.
1/60th at 24p looks much different than 1/60th at 30p,
and I'm more used to seeing the 24p version.
And this difference is dramatically increased
when switching to 60p. However, I do find
that reducing the shutter speed when shooting 60p
does reduce some of that soap opera effect
and I definitely would rather watch 60p at 1/60th of a second
than 60p at 1/125th for real-time playback.
Again though, for slow motion, I'd rather have 1/125th.
But let's see what other people have to say.
-Honey? -[woman] Yeah?
-Are my zebras at 55? -[woman] Yeah.
Yeah? Because I'm making a video for Gerald.
-[woman] OK. -So, you know...
OK. OK. Hi Gerald! How are you? Nice to meet you.
Jordan Drake here from DPReview TV, and I was able
to take a look at the files that Gerald recorded.
Excellent job with the screwdriver there, Gerald.
OK, so, I just watched the clips, and there's a lot of
really interesting stuff happening there in my brain.
Since I lack the technical vocabulary
to adequately explain my observations,
I'll just do what they do on Sci-Fi TV and make stuff up.
If I got any or all of these answers wrong,
it's only because I copied off of Tyler Stalman.
I have no idea what Gerald is trying to get me to look at
with these, so hopefully I said something useful.
So, let's start with this one.
I don't like the way this looks.
A lot... I find it a little choppy.
The 24 at 1/125th had the most separation. Huge separation,
and just looked all shades of janky as well.
Most of all, what needs to feel right in these
is that that ruler, that spinning object,
feels like it's just one physical thing.
Sometimes, especially, like, 24 frames per second at 125th,
it would start to, kind of, break apart
and the stuttering effect would make it feel like there
are more than one rulers spinning around. That starts
to break the illusion of reality in a bad way.
This is... this is fantastic.
It's, uh, fluid. I like this a lot.
The control shot, the 24 frames per second at 1/50th shutter.
I thought it definitely had, like, a cinematic vibe to it.
Uh, which, I mean, obviously, that's what we talk about,
but I thought that was really interesting
that I could see it, even though it was just, like,
a spinning piece of cardboard on a drill.
It definitely had that movie, kind of, vibe.
And this one has the soap opera effect.
Which I sometimes enjoy, but...
the one above it, the 50th one...
looks the most natural to me.
The 60 at 1/50th looked the most like the control.
Just separating on the down arc, and coming back together
on the up, with a good trail, while not being
really fussy about it.
OK, so this looks really good.
And then for the slowed down one,
I liked the 60 frames per second at 1/60th shutter,
which I also thought was really interesting.
The 60p slowed to 1/60th looks just blurry-e.
Like there's a glow, more than a trail.
A 60th of a second shutter speed looks...
pretty weird to my eyes. Now, I've actually used this before
if I know I'm going to be slowing the footage down
and I want things to look like they were moving faster
than they actually did, then 60 frames per second
at 1/60th of a second is useful, but for general shooting
I'm going to follow the old 180° rule,
and when you're shooting at 1/125th of a second,
it just looks better to me.
And this one...
looks choppy. The second slowed down one.
This looks very bad. It's-- this almost looks like
it's interlaced. It's like trying to refresh the frames.
-I don't like this at all. -Those both actually felt real.
You know, the 60th would be weird with other motion,
but the blur really made it feel like one unified object,
but there is something interesting about
the 60 frames per second where it really feels tangible,
and feels directly in front of you. So, in this example,
I liked the 60. It was actually pretty cool to watch.
[Gerald] Alright, so let's wrap up.
Most people suggested that over-cranking your shutter
when shooting at 24 frames per second
looked kind of choppy. Most people also thought
that the 60p footage that wasn't slowed down
and that was shot at 1/125th
had the greatest soap opera effect and was least desirable.
And everyone thought that the 24p at 1/50th
looked the most natural. But I'll be the first to admit
that this is likely due to years of conditioning
and exposure to a standard that stretches back
to before we were born. The most interesting
and most polarizing comparison
was the slowed down 60p footage though.
Some people preferred the 180° rule at 1/125th of a second
and some preferred the blurrier 1/60th shutter.
I personally think the 1/60th version is wrong
from a physics standpoint, objects moving that slowly
shouldn't blur that much, but I do agree
that shooting slow motion at a 360° shutter is a neat effect
and could be desirable for creative purposes.
So if we tried to wrap this up into a simple tip to remember
it would be yes, keep using the 180° rule
for anything that involves real-time playback at 24, 25,
or probably even 30p, and for any slow motion video
beyond those frame rates. But use a 360° shutter angle
for frame rates above 30p if you're delivering
at those higher frame rates for real-time consumption.
So 1/60th of a second shutter for non-slow motion
60p delivery for example.
Or just do whatever you want. What do I care?
Uh, the 125 frames per second, and, uh, 60th of...
Some people preferred the 180° rule at [stammering]
What am I saying?
100, and 100, and 125th of a second.
And my, uh, voice is OK? It's not clipping?
[woman] Uh, say something. Do a little--
Test, test, test. Gerald.
Gerald Undone. Done, done, Gerald Undone.
-[woman] Yeah, you're good. -He's-- yeah. OK.
Because he's crazy.
[Gerald scatting]
I'm capturing the screen.
Uh, Gerald, if you want, you can use
the capture screen too.
Very nice. I like it.
Thank you, Gerald. See you later. Bye.
But that's going to be it for me. I hope you found
this video entertaining, or at least helpful.
And if you did, make sure you leave it the old thumbs up
and consider subscribing if you haven't already.
But if you did not find this video helpful or entertaining,
try setting the playback speed to 75%.
All right. I'm done.