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What is Exposure Triangle for Filmmakers? Aperture, Shutter and ISO Explained. - YouTube
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Hi I’m Sareesh Sudhakaran.
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In this video I’ll explain the exposure
triangle as simply as I can.
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If you are a complete beginner who’s looking
at all the aperture, shutter and ISO numbers
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on the camera and tearing your hair out, you’ll
love this video.
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No, it won’t bring your hair back, more
like a wig so you can cover up your mess.
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Let’s start with ISO.
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It’s the simplest thing to understand.
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A piece of film is a chemical, like a piece
of paper.
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There’s a limited amount of water a piece
of paper can absorb before it is overwhelmed.
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The same with film.
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It’s literally like baking bread in an oven.
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Give it the perfect time and it cooks perfectly.
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Too much light and it overwhelms the film.
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You get pure white.
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Too little light, and it turns dark and muddy.
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Film is sensitive to light, just like paper
is sensitive to water.
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This sensitivity is a fixed thing.
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It doesn’t change over time.
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That makes your job easier.
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Once you know the exact amount of light required
to expose film, it never changes.
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Like a recipe that calls for one cup water.
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It’s always going to be one cup of water.
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You can measure this water in litres or ounces,
or milliliters, whatever’s convenient to
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you.
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Sensitivity in photography is measured in
ISO.
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ISO stands for International Standards Organization.
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They have guidelines for how this should be
measured.
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ISO is just a number.
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Don’t get hung up on the technical details,
they are not important to beginners.
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A pilot only needs to know how to fly a plane.
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A pilot doesn’t have to build a plane.
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So let’s talk about the interesting bits
about ISO.
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The only thing you have to know about ISO
is, the greater the number, the better the
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camera sees in low light.
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Double the ISO, and the camera needs half
the light.
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For a beginner it’s not easy to grasp what
this means.
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Let’s say you’re in the middle of an open
field on a sunny day, and you need ISO 25
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to expose a frame.
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Now, what if you had ISO 800?
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You would get the same exposure with just
a candle.
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Okay, candlelight won’t reach the rest of
the land, but you get the idea.
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It’s incredible technology.
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Let me show you something cool.
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A hundred years go, film had a rating of ISO
25 or so, on average.
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They didn’t rate film stock in those days
so people had to expose and develop by eye.
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They needed tons of light to shoot anything.
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Portraits were always outdoor or near large
windows.
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Charlie Chaplin shot on stages that had overhanging
diffusion on top so sunlight could light the
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set.
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Yes, gorgeous soft light is as old as cinema.
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Slowly but surely, film came in higher sensitivities.
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ISO 50 was a big jump.
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The gorgeous M by Fritz Lang was shot at about
that ISO (Kodak Type II Cine Negative 1218).
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Then came ISO 100, 160.
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Citizen Kane was shot on ISO 160 film (on
Eastman Super-XX).
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The higher the sensitivity the higher the
number.
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You double the number, and you only need half
the light.
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If Citizen Kane was shot on ISO 160, double
that is ISO 320, and that jump happened a
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couple of decades later (with Eastman Tri-X
5233).
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The Night of the Hunter was shot on film rated
at ISO 320.
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Just as a side note, this was just for black
and white film, color film was still stuck
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at ISO 25 or so.
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E.g., the beautifully shot Vertigo was shot
at (Eastman 25T 5248) ISO 25.
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Modern cameras don’t even have an ISO 25.
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Modern cameras start at about ISO 100, with
some exceptions.
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Guess what was shot on ISO 100?
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The Godfather was shot on ISO 100 (Eastman
100T 5254).
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Gordon Willis played with underexposure so
much so that he earned the moniker ‘the
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prince of darkness’.
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A decade later Kubrick shot The Shining at
ISO 100.
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Color film hasn’t developed as quickly as
black and white.
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Fast forward today, and Once upon a time in
Hollywood used (Kodak Vision3 200T 5213) ISO
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200 for daylight, and (Vision3 500T 5219)
ISO 500 for low light.
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And this is where digital sensors have taken
over.
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A sensor is like a piece of film that can
change its sensitivity by some magical will.
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Like mood swings.
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Today you are touchy, other days you have
a thick skin and nobody can get to you.
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The best sensors today can shoot cinematic
images at ISO 3200 or 6400.
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There are cameras that go way beyond to almost
4 million ISO and I’m pretty sure in the
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future we’ll go even further.
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In the past ISO was limited by the chemistry
of film.
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Things are very different now.
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In some cameras the change in sensitivity
is made by software.
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The sensor records the same thing, but through
software you can change the sensitivity later
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in post to whatever you want.
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So instead of paper, we have a towel.
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If it gets too wet, wring it out, or, add
more water if you want.
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The limitation with ISO is actually in the
opposite direction.
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Cameras go down to ISO 100, some can’t go
below ISO 800 if you want the best image quality.
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Some DSLRs go to ISO 50, but what if you could
go lower?
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Today we use ND filters to cut down light,
but if we can reduce ISO to extremely low
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numbers we won’t need ND filters anymore.
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So I hope the next big revolution will come
the other direction.
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So, as a beginner, what should you do with
ISO?
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I have some advice for you.
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Don’t touch it.
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Set it at Auto ISO and forget about it.
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You don’t want to auto everything, but set
your ISO to auto in the beginning.
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Why?
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The ISO is a functional tool.
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It doesn’t change the way your image looks.
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For the creative part of image making you
need the other two members of the triangle.
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The simpler to understand is the shutter.
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A shutter is exactly that, a shutter that
opens and shuts.
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Like a window.
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In our example with the paper and water, you
have to start pouring water, and you have
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to stop sometime.
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That’s what the shutter does, it starts
and stops light hitting the sensor.
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On cameras it’s written in seconds and minutes.
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In modern cameras the shutter can stay opened
for hours or as low as 1/8000s.
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Having this range is powerful.
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If nothing moves while the shutter is open,
the image is sharp.
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But if there is movement, like water flowing
or clouds moving across the sky, they all
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get exposed while the shutter is open and
it blurs everything together.
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You can create stunning photographs this way.
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You can also capture faint stars by keeping
the shutter open for hours.
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And, what if you want to freeze droplets,
or you’re shooting a fast moving formula
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one car?
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You can’t keep the shutter open for too
long.
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When things move during the time the shutter
is open, the blur you get is called motion
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blur.
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Blur caused by motion.
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This motion blur is undesirable in most photography,
but guess where it is critically important?
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You bet, cinema.
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In cinema, there is a standard shutter duration
that cinematographers follow to this day.
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The shutter is kept at about 1/48s, keeping
it very simple.
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This produces a motion blur that people have
got used to over a century of watching films.
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When Peter Jackson tried to change that for
The Hobbit, a lot of people didn’t like
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it.
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Hold on there, wait a minute.
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Didn’t Peter Jackson change the frame rate?
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Whenever you expose a photograph, that’s
one frame.
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In cinema, there are 24 frames a second.
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This means you have to open up the shutter
24 times in one second - to capture 24 frames
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per second.
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This also means you have to close the shutter
24 times a second.
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That’s 48 total per second, which is why
the shutter speed is 1/48s.
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When Peter Jackson increased the frame rate
of the Hobbit to 48 fps, the shutter would
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have been opened and closed a total of 96
times, for a shutter speed of 1/96s.
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This made the images crisper, and reduced
the motion blur people are used to.
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The reduced motion blur changed the impression
of movement.
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It is useful in sports.
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Sports are shot and broadcast at high frame
rates so you can actually see the ball traveling
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fast.
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Otherwise you’ll see a blurry mess in tennis,
football, table tennis, Mohammed Ali’s punches.
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In chess, you can keep the shutter open for
hours...and hours.
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I love chess, so I’m allowed to make fun
of it.
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You can change shutter speeds if you want.
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If you want less light, you can keep your
shutter open for a smaller period.
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If your ISO is low, you can open the shutter
for longer to let more light through.
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So this way ISO and shutter work like a balance.
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You raise one, you lower the other, for the
same exposure.
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In film the sensitivity is sometimes called
speed, like film speed - not the film Speed,
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film speed.
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Maybe that’s how the word shutter speed
came to be.
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It doesn’t have to make sense, just like
ISO.
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You can call it shutter duration, or just
shutter.
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Or just shut up and shoot, don’t call it
anything.
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As a beginner here’s a simple tip.
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You can think of the shutter as the inverse
of the ISO.
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E.g., if ISO 100 and a shutter of 1/100s gives
you one exposure, then changing the ISO to
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50 will mean you must change the shutter to
1/50s. 1/50s is longer than 1/100s, so when
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you reduce the ISO by half, you reduce the
shutter speed by half.
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That relationship is always maintained.
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Don’t worry if these things don’t make
immediate sense.
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The first time you learned about feet or meters
or kilograms as a kid, you probably didn’t
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get it either.
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It takes a fair bit of time for kids to even
get their own name.
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I get it, you’re not a kid.
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You have hair growing in all kinds of places
now, but not in your brain.
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That got left behind.
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Aperture.
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The aperture is the one thing that’s not
in the camera, but in the lens.
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Every lens is made of glass, and it has a
fixed diameter.
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Optics is a complicated field, but to keep
it really simple, for you, this diameter is
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the opening.
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The lens focuses the light and makes an image
on the sensor, and the opening decides how
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much light can pass.
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It’s like a window into a room.
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There might be sunlight all around outside,
but only the light that comes through your
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window reaches your room.
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Here’s a fun little puzzle.
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The light that passes the opening must travel
through the lens to the sensor.
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When light travels, it always loses intensity.
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I have explained this in another video, and
it’s called the inverse square law.
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No, you don’t have to know anything about
it.
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Just remember, the diameter of the opening
and the distance it has to travel decides
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how much light hits the sensor.
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If you want to reduce the light, you can reduce
the size of the opening.
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A mechanism that does this, is inside most
lenses.
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It’s called the aperture.
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Aperture means opening.
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Again, it doesn’t have to make sense.
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What you have to know though, is that the
aperture was designed because ISO didn’t
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exist at the time.
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They needed something other than the shutter
to control light, so they could work within
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the limitations of light.
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The technology comes from telescopes and microscopes.
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Cameras don’t have to be so precise.
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Over a hundred years of photography, people
realized this crazy aperture had some cool
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tricks.
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If you open up the aperture you let in more
light, but fantastically, you also get smaller
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depth of field.
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This means the background gets more blurry,
very useful for portraits or cinematic close
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ups.
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Now, you don’t want that for landscapes
or crowd scenes, where seeing everything is
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important.
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It is also critically important for macro
shots.
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When you get closer, you need to make the
aperture really small so the entire insect
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is in focus.
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There are other things that happen when the
aperture is changed, but that’s not so important
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for beginners.
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All you have to understand is that aperture
and shutter have two relationships.
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Like Mr and Mrs. Smith.
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They are husband and wife, but they also want
to kill each other.
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When one shoots the other ducks.
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It’s exactly like the ISO and shutter.
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You can’t raise both.
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Let’s say you are standing in the open ground
on a sunny day.
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You want a blurry shot of a flowing dress,
but you want the background blurred as well.
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You have to open the aperture and keep the
shutter open longer.
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That will let too much light in.
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To solve these kinds of problems filters and
lights are used.
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Or maybe in the future you can reduce the
ISO to compensate.
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These are like a marriage counsellor for Mr
and Mrs Smith so they can get along together
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long enough to create babies, I mean baby
photographs.
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Now for the last part of the puzzle, those
crazy numbers on the lens.
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ISO and shutter are written in simple numbers,
not very hard to understand.
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Aperture is written in weird numbers, and
this throws off most beginners.
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Remember, the International Standards Organization
has certain rules for how cameras should measure
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ISO.
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Unfortunately it gives camera manufacturers
some leeway so they don’t always agree,
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but that’s another matter.
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At least there are rules.
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For a beginner, ISO 100 in one camera should
give the same result as ISO 100 in another
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camera.
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As far as shutter speeds are concerned, it’s
a mechanical thing that is controlled by time,
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like a wristwatch.
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1/50s for one camera should be 1/50s for another
camera.
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But with aperture, it’s inside the lens.
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Every lens is different.
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Even comparing the same lens made by two manufacturers,
the optics inside are different.
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The diameter of the lens is different.
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The distance to the sensor is different.
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And remember, we know that these are the things
that control the amount of light falling on
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the sensor.
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In other words, the aperture controls the
exposure.
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But how can we have one setting that all lenses
must follow?
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There have been many aperture systems in the
past.
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E.g., the earliest was in the early 1900s,
by Franz Stolz.
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It went like this: I’m going to use a ruler
next to it so you understand it better.
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Then there was another system, that went like
this: And a third system, used by Kodak in
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its early days, that went like this: It was
only in 1949 that the world finally decided
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to adopt the system we have today.
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You might have a valid question.
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Why don’t they use a linear system, like
a ruler?
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Look at a bright landscape photograph.
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There are areas that are bright, and areas
under trees or bushes that are dark.
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You could place a black box and it will be
really dark, and you can have the sun in the
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shot and it can be really bright.
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This means a camera should be able to capture
not the light falling on the scene, but the
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light reflected off everything.
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And light reflects differently.
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Through trial and error, they understood that
the amount of light in our world created by
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the sun is tremendous, and you had to double
or halve it to keep things under control.
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We can measure distance in kilometers, but
when we start measuring distances between
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stars, we need light years.
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Units are chosen for convenience.
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Every doubling of the light is called a stop.
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And even though the number on the aperture
is technically called f-numbers, everyone
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calls them f-stops.
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Just like shutter speed, we have f-stop, a
marriage of words.
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The reason why it’s called f-stop, is because
each major jump is the doubling of light,
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or double the exposure.
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If you want a scale with 1, 2, 3, you can,
with f-numbers.
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F-numbers can be any number except zero.
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But with f-stops, each step is double the
previous one, or half the previous one, depending
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on the direction you are counting.
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To start this ruler they thought 1 was a good
starting place.
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They didn’t know we’d have f/0.7 and f/0.95
lenses when they made this system.
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They thought f/1 was going to be it.
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By the way, f-stops are written as f/number
because on the lens you also have another
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linear scale, the focus scale.
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This is a way to differentiate between the
two and to tell you the f-stop is inverse,
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the larger the number, the smaller the aperture.
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This is the other confusing part about f-stops.
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Like bikes that have the gear reversed.
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It takes some time to get used to, but you
will.
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To get one, you just raise a base number by
zero.
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But the rest depends on what this base number
should be.
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It can be anything really.
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You could use 2, or 2000 or 124, doesn’t
matter; or you could use root 2.
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A foot didn’t have to be 12 inches, it could
have been 13 inches and we’d all be following
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that.
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I made a video on aperture a few years ago
and many people asked me why root 2 was chosen
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over 2.
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I don’t have the exact answer, but I have
a guess.
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Look at these numbers.
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In the early days of photography, a great
man by the name of Ansel Adams created the
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Zone system, with 10 stops.
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This was the latitude of film in those days.
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That means you could expose on a sunny day
and expect to see the range from bright to
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dark in 10 stops of light, 10 jumps on the
scale.
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Of course, today we know there are way more
stops than that, but let’s stick to 10 because
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that’s what they had.
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On this chart pick 10 jumps starting from
1 and you’ll see, if you use 2 as your base,
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the numbers get really big very fast.
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Lenses were small, and you had to etch the
numbers on it.
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There wasn’t much space, which is probably
why root 2 was chosen.
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Kilometers versus lightyears.
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Root 2 gives you smaller numbers.
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Each number represents a difference of one
stop of light.
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When you close down the aperture by one stop,
you are halving the light.
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Set your camera to full auto mode and point
to a scene.
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Note down the aperture, shutter and ISO settings.
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Now turn the camera to manual mode.
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If your camera changes settings turn the aperture
shutter and ISO to the earlier settings.
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You should see the same image.
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Now, close down the aperture by one stop.
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E.g., if it’s f/2.8 as shown here, I’m
changing it to f/4.
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The scene becomes darker, because by closing
down the aperture we have lost half the light.
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To compensate, I could either open the shutter
up by one stop, or the ISO by one stop, or
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both in half stops.
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However, if you’re a beginner, start by
thinking of aperture as the setting that lets
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you create blurry backgrounds or make everything
in focus.
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That is more practical, and more fun.
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Let the shutter and ISO change to balance
the exposure.
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If you’re shooting videos, the shutter is
fixed at 1/48 or 1/50s, then you only have
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aperture and ISO to change.
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Keep one fixed, and change the other two.
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Change both or change all three.
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They are all married together, for life.
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Like musical notes, they can be played in
different ways for different effects.
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This is the exposure triangle.
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An elegant solution that has lasted hundreds
of years.
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Please remember, back in the 1920s they didn’t
have ISO ratings on film stocks, they had
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to develop in the dark room by eye.
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They didn’t have light meters so they couldn’t
measure precise exposure.
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The shutters were not so precise, the lenses
were not so sharp.
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They used the only thing they had - their
eye.
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No, you idiot..exposure triangle.
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