CD / Shutter Speed

Summary

The video explores the evolution of camera shutter mechanisms, from early uncoverers of lenses to leaf shutters to rotary disc shutters in film cameras. It explains how electronic shutters in digital cameras work, enabling adjustable speeds. However, the rolling shutter effect causes distortion. While mechanical shutters avoid this, most cameras use CMOS sensors with inherent rolling shutter. Some companies seem complacent about the artifact. Ultimately, global shutter technology may restore image integrity, if manufacturing improves affordability.

Takeaways

• 😯 Early cameras required long exposure times, limited by media sensitivity
• ⚙️ Mechanical shutters enabled adjustable exposure times
• 🎥 Rotary disc shutters enabled motion pictures by syncing frame rate and exposure
• 📽️ 180 degree shutter angle at 24fps became the cinematic standard
• 🖥️ Electronic shutters in video cameras enabled flexible exposure times
• 🤯 CMOS sensors enabled higher resolution but caused rolling shutter artifacts
• 😵‍💫 Rolling shutter can distort fast movement in unpredictable ways
• 🌀 Mechanical shutters can also exhibit rolling shutter, but it's less noticeable
• 💸 Global shutter sensors are technically possible but more expensive
• 😕 Most people don't notice or care about rolling shutter issues

Q & A

Why were early cameras just boxes that you had to uncover the lens on for a period of time?

Early photographic processes required long exposure times to accumulate enough light to capture an image. Uncovering and covering the lens was a simple way to control the exposure time.

How did the advent of motion pictures impact shutter technology?

Motion pictures required capturing images much faster, at 16 frames per second or more. This was beyond the capability of traditional shutters, so the rotary disc shutter was invented to produce intermittent exposures by spinning a disc with cutouts.

What is the difference between shutter speed and shutter angle?

Shutter speed measures exposure time in fractions of a second, while shutter angle measures exposure as a percentage or proportion relative to the duration of a movie frame at a given frame rate.

How did electronic shutters in video cameras differ from traditional mechanical shutters?

Electronic shutters could be much faster or slower than mechanical ones, with exposure times adjustable down to a fraction of the frame rate. But they still needed a tiny gap to read out the image sensor.

What causes the rolling shutter effect in CMOS sensors?

In CMOS sensors, rows of pixels are read out sequentially. So each row captures the scene at a slightly different point in time, causing distortions of fast movement.

Why don't rotary shutters seem to cause rolling shutter artifacts?

The rotary shutter sits far in front of the unfocused light. So any artifacts get diffused. And with fast spinning shutters, distortions happen faster than our eyes perceive.

What is an electronic first curtain shutter and how does it impact bokeh?

It starts exposure electronically and ends it mechanically. This shifts the bokeh due to the physical difference between the start and end points across the sensor.

What is global shutter and why isn't it more widely adopted?

Global shutter exposes all pixels simultaneously, avoiding rolling shutter. But it's more expensive to manufacture, and most consumers either don't notice or don't care about rolling shutter artifacts.

How can you measure rolling shutter speed?

It's measured in milliseconds - the time it takes the sensor readout to scan from top to bottom. Faster sensors have lower rolling shutter durations.

Will global shutter eventually replace rolling shutter?

As manufacturing techniques improve, global shutter is becoming more affordable. It may eventually be ubiquitous in phones and consumer cameras, eliminating rolling shutter artifacts.

Outlines

00:00

🎥 A deep dive into the mechanics and history of camera shutters

Explains what a camera shutter is, how it works to control exposure time, and the evolution of shutter mechanisms from early cameras to modern digital video.

05:01

📷 How rolling shutter causes distortions in digital cameras

Describes rolling shutter artifact caused by CMOS sensors, how it differs from focal plane shutters, and why mechanical shutters also show some distortion.

10:02

🤔 The conspiracy of CMOS sensors and rolling shutter

Humorously suggests camera companies are secretly fine with rolling shutter issues, though global shutter is possible and may become standard some day.

Keywords

💡shutter speed

Shutter speed refers to the amount of time the shutter is open to expose the film or camera sensor to light. It is a key concept in both film and digital photography and videography. In the context of this video, shutter speed is discussed in depth - from early cameras with manual shutters to modern electronic shutters. It relates to the core message about the history and evolution of shutters.

💡rolling shutter

Rolling shutter is a phenomenon in modern digital cameras where distortion occurs because the rows of pixels in the camera sensor do not all start and stop exposing at exactly the same time. This video explores rolling shutter extensively, defining what it is and delving into why mechanical shutters do not have the same issue.

💡global shutter

Global shutter refers to camera sensors where all the pixels start and end the exposure simultaneously, avoiding the rolling shutter effect. The video contrasts this with rolling shutter and suggests global shutter cameras may become mainstream in the future.

💡rotary shutter

A rotary shutter is a circular disc placed between the lens and film plane with cutouts that spin, enabling intermittent exposures on film cameras. The video explains how rotary shutters enabled motion picture cameras and their relationship to concepts like shutter angle.

💡shutter angle

Shutter angle relates the amount of time a rotary shutter exposes the film to the duration of each frame in a motion picture camera. The video explains shutter angle allows standardizing exposure relative to the frame rate rather than absolute time.

💡CCD sensor

The video discusses how CCD (charge-coupled device) sensors in early digital video cameras differed from film and enabled features like electronic shutter. But it also covers their limitations with resolution and electronic rolling shutter.

💡CMOS sensor

Complementary metal-oxide semiconductor (CMOS) image sensors are more modern digital camera sensors that read pixels row-by-row, enabling higher resolutions but causing the rolling shutter effect extensively discussed.

💡focal plane

The focal plane refers to the film plane or camera sensor surface that captures the image. The video explains how the distance of the shutter from the focal plane impacts perceived distortion from shutter motion.

💡exposure time

Exposure time is the duration the film or camera sensor is exposed to light to produce an image. This core photography concept interlinks shutter speed, shutter angle and the evolving history of cameras covered in the video.

💡bokeh

Bokeh refers to the aesthetic quality of out-of-focus areas in a photograph. The video touches on how modern hybrid shutter mechanisms impact bokeh, much to the dismay of photographers.

Highlights

The earliest cameras were just a box that accumulated light over a tedious amount of time before covering the lens back up.

As photosensitivity increased, exposure times decreased, making images less motion-blurry, but timing the short exposures became important.

Shutter mechanisms were designed to close in the opposite pattern of how they opened so all particles on the film plane spent equal time exposed.

Rotary disc shutters with mirrored sections were used in movie cameras to alternate between exposing the film and directing light to the viewfinder.

The standard cinema shutter angle of 180 degrees exposes film for half of each frame's duration at 24 fps.

Electronic shutters in video cameras can be much faster or slower than mechanical ones, no longer bound to physical limitations.

CMOS sensors can start reading out the next exposure before the previous one is fully read, enabling rolling shutter artifacts.

All shutters move across the image plane, but mechanical ones are usually too fast for rolling shutter distortion to be visible.

The position of mechanical shutters away from the focal plane and diffusion through unfocused light hides their movement.

Large, slow shutters in old cameras did cause cartoonish rolling shutter effects.

Hybrid electronic first curtain shutters subtly impact bokeh in ways that frustrate photographers.

Global shutter sensors with per-pixel storage could eliminate rolling shutter, but are currently too expensive for most applications.

While some care about rolling shutter, most consumers don't, removing incentive for global adoption of global shutter technology.

CMOS inventor commercialized the technology that led to widespread rolling shutter through the most popular cinema cameras.

A few advanced sensors nearly match mechanical shutters for rolling shutter performance.

Transcripts

What?

What?!

Too much exposure for you?

Well, excuse me!

[metal rattles]

[short synth jingle]

The shutter is...

Cameras need...

[exhales]

There’s no such thing as infinity in the physical world.

Just as the tallest mountain has a peak,

a snapshot of the tiniest moment

is actually a record of a period of time.

In cameras, we call the setting

that controls that period shutter speed.

Why?

As usual, because of olden times.

-[Ragtime music plays] -The earliest cameras

were just a box.

You uncovered a lens, let light accumulate inside

for a tedious amount of time,

then covered the lens back up.

This made selfies extremely challenging.

-[Camera snaps] -As the photosensitivity

of the medium inside the box increased,

exposure times decreased.

Things got less motion-blurry

but it became important to get the short timing

of the exposure just right. [mechanical clatter]

Jobs of hard working lens uncoverers

were lost to cheap, newfangled mechanisms

such as guillotine shutters,

leaf shutters and Packard shutters.

The best designs made sure to close in the opposite pattern

of how they opened,

so that every particle on the film plane

spent exactly the same amount of time in the light.

[Irish accent] But nothing could have prepared the industry

for the disruptive technology of motion pictures.

The rigorous demands of taking

upwards of sixteen photographic images per second

were beyond the capabilities of traditional shutter designs.

Luckily, there was a simple solution:

Convert spinny motion into intermittent motion.

The standard in pretty much all movie cameras

from the time of Lumiere brothers

to the century in which I began to be alive,

has been the rotary shutter:

a disc with a wedge cut out that spins at a constant rate

between the lens and the gate that lets light in.

Of course in practice, it's actually much cooler:

the wedges are doubled so the disc can spin

half as fast and it's angled 45 degrees

and has a mirror surface,

so that between exposures light is bounced

to a viewfinder, so you can see what the hell you're filming.

You might ask, "Captain, you're very smart,

but if we're now capturing continuous motion,

why do we need a shutter at all?"

Well, because it's still the past.

We're still burning discrete picture rectangles

onto a film strip

and the camera needs time in the dark for a scary claw

to advance it to the next picture-burning spot,

usually about half the time

of the whole frame capturing process.

So two distinct things, the frame rate

(how many pictures are taken per second)

and shutter speed (how much of one picture's time slot is spent

actually capturing the light)

are cleverly mechanically synced up.

This is where we get the cinematic concept

of shutter angle, measuring exposure relative to

the life of a movie frame,

as opposed to the primitive still photography idea

of shutter speed, measured in fractions of a second.

You just have to get used to conceptualizing

slices of a hypothetical pie as a percentage

of an arbitrary unit of time.

Like a novelty Japanese watch.

As movie cameras improved,

it was possible to just barely increase the shutter angle

to around 200 degrees.

Of course it could always be decreased,

so you could artistically symbolize the carnage

of an ancient Roman battle with sharp staccato frames.

But if you wanted to symbolize the delirious aftermath

of the ancient Roman battle with blurry, streaky long exposures,

you had to actually lower the frame rate.

But honestly, no one wanted to dig into the camera

to switch the little disc.

You had to tell the rental house in advance...

180-degrees was fine.

Aside from specialty high-speed cameras

that used crazy things like a rotary prism

to expose continuously sliding film,

exposure time of half the frame rate

became the unspoken standard in cinematic art.

And since the world agrees that 24 frames per second

is the best frame rate,

all the most iconic images in our collective movie memories,

from Star Wars to... Star Wars,

are built out of 1/48th of a second moments in time

held on screen for twice that long.

And now it's time to forget all that

because the concept of capturing images was completely reimagined

in the electronic age.

Film was out

and the capture medium became...

tubes, which... we don't have time for that.

But eventually, it became something like film again:

an array of photosensitive silicon pixels on a chip.

This was the CCD.

Now the shutter wasn't a shutter at all,

but a decision about how long to let the pixels

get bombarded by photons

globally, all at once,

before having them pass the loose electrons

they collected to each other, down the array,

like a bucket brigade,

to be transformed into voltage fluctuations

that could be read out as a video signal.

Unshackled from mechanical parts

electronic shutter speed could now be crazy fast

or crazy slow,

even the entire duration of a frame!

Well, almost.

This is a DSR-370,

the sickest early 2000s broadcast camera

a superhero could afford straight outta’ space college.

Look at its adorable little "1/2-inch type" CCD.

There are actually 3 of them in there,

but don't worry about that.

Like all North American cameras of the time,

it was hardwired to shoot in standard definition

at 29.97 frames

- or 59.94 interlaced fields - per second.

The idea of making the shutter

even faster than that refresh rate

seemed silly most of the time.

But if you really wanted to change it,

to avoid flicker when shooting a CRT monitor or something,

there was a physical switch to engage the electronic shutter

Then you could set it in either fractions of a second

or more precisely in hertz.

Note that the slowest you could set it was 60.4 Hz.

It's not true 360-degree shutter

because you needed that tiny bit of time

to read out all the pixels and reset them

for the next exposure.

The more pixels there are, the longer that process takes.

And that's the problem with CCDs.

They weren't scalable enough.

When the OtherSpawn of Omega Draconis gifted Earth

the corrupting technology of High Definition Television

in early 21st century,

humanity suddenly needed a cheaper way

to capture much larger images

at increasingly obnoxious frame

Enter Active Pixel CMOS sensors.

In these, each pixel transforms its own loose electrons

into a voltage and sends it off, a row at a time,

to the part of the chip

where it's converted to a digital signal.

This is much more efficient because...

why should these freed pixels above be idling

and taking bathroom breaks

when they could already be capturing the next image!

As one exposure rolls off the chip,

the next can start rolling in.

You know, like a sort of...

[gasps] Oh, no.

-Rolling shutter!!! -[boulder rumbles]

We've all seen them:

skewed, wobbly or completely scrambled images

that happen in digital cameras

because that CMOS sensor readout sweep means

consecutive rows of pixels capture slightly different

moments in time.

Whether the shutter speed is long or short,

the sweep is always the same

and fast-moving objects are bound to be distorted.

At first glance it seems like something you could

compensate for in post

by shifting the rows back into alignment...

until you realize that the shift varies

depending on the speed of the motion.

In some cases you could use

sophisticated tracking and remapping,

but there's still nothing you can do about that.

Or that.

Rolling shutter is unfixable

and present in almost all modern footage.

Some hate the artifact

because it used to not be a thing and now it is.

Others don't care because they grew up with it

and think this looks fine.

And a select few are gradually driven to madness

by a simple question:

"Captain, all mechanical shutters

are literally rolling shutters.

They all travel across the image,

sometimes in exactly the same pattern

as an electronic shutter.

How come they don't cause the rolling shutter effect?"

The answer is...

they kinda do.

Mechanical shutter curtains and CMOS sensor readouts

move at a constant rate

regardless of the shutter speed setting

and faster speeds are achieved by

more closely staggering the mechanisms

that start and end exposure,

narrowing it to a slit.

It’s just that in most stills cameras

available to most people today

the mechanical shutter fires...

way faster.

So fast, you usually just

can’t perceive the distortion with the naked eye.

Another factor in why even

a narrow angle rotary disc shutter

seems to avoid rolling shutter artifacts

is a little thing called the lens.

It’s there to focus light perfectly on the focal plane.

But the shutter is way out in front.

Here, the light is still unfocused,

and any disruptions to it appear diffused.

It’s the same reason changing the aperture inside the lens

doesn’t show up as an actual iris in the image,

but as an overall change in brightness.

Of course, it’s a matter of proportion.

In very old, large format cameras,

where a giant shutter was near a giant glass plate

and moved relatively slowly,

it actually did cause a funny kind of rolling shutter.

Some even say it’s where we got the classic concept

of cartoon speed distortion.

But even for modern stills photographers,

with their lightning-fast focal plane shutter DSLRs,

the physical position of the tiny curtain

makes a difference.

It's funny, some cameras do this hybrid thing

called "Electronic First Curtain Shutter"

where the exposure is started by the sensor,

then the mechanical shutter closes to end it,

and the optical discrepancy between the two

has a weird effect on “bokeh,”

the blobby bright spots in out-of-focus areas

that photographers are obsessed with.

And it's hilarious to see them cry about it,

"Oh, my bokeh! My precious bokeh!

Look what's happened to it, oh no!"

[chuckles]

Despite what experts on Reddit say,

it seems like in general, people are bothered

by rolling shutter defects.

Consumers comment on it whenever they see it.

Folksy educators make videos about it.

VFX artists hate how it makes tracking and compositing

less accurate.

And yet, we're forced to just accept it.

I’m not saying it’s a conspiracy...

I’m just saying...

The CMOS sensor was initially commercialized

by a guy from NASA JPL

who started a company

that got bought by another company,

renamed, then sold to a semiconductor giant

which itself rebranded,

and now supplies sensors to the most popular

line of professional cinema cameras in the world,

which all have rolling shutter!

To be fair, they did try a mechanical shutter version,

but it didn’t catch on.

And to be even more fair,

not all rolling shutter is created equal.

The actual readout speed of different sensors varies a lot.

Nerds who test new cameras have ways of measuring it

in milliseconds.

And while in some cameras it spans

almost the duration of a frame,

a few of the best ones have rolling shutter so minimal,

it rivals mechanical shutter.

But it’s perfectly possible to expose the whole frame at once,

to have “global shutter” in a CMOS sensor.

Every pixel just needs its own capacitor

to store the exposure until it can be read out.

That makes it more expensive.

But as manufacturing processes improve,

it is becoming... almost affordable.

Before you know it, global shutter cameras

will be in phones and we might finally

get back to the integrity of images we had

in the early 1900s.

Imagine:

Global adoption of global shutter.

Although...

Most people don’t care,

so there’s not a ton of incentive for it.

[outro music plays]

There’s not a ton of incentives for anything anymore.

Ever feel that?

It’s like... we finished a video game

and now it’s the end credits.

But we keep mashing the controller

like it does something.

It’s the credits, man.

[music transforms into a melody from ‘Sonic 2’]

It’s the part in the Sonic 2 credits medley

-where the drums go -[taps in time with drum solo]