What Is Aperture? Aperture & f-stop explained!

Let’s unpack it together in this photography tutorial.

what is aperture - aperture and fstop explained for beginners

Home / Photography Tutorials / What Is Aperture? Aperture & f-stop explained!

What Is Aperture?

A simple explanation of Aperture & F stop!

When it comes to learning photography basics, the terms can be a little daunting! Nowhere is this more the case than with aperture. The problem is there aren’t a lot of good tutorials explaining what aperture is and how aperture works – So we decided to sit down and tackle aperture in depth. Not just the technical definition for aperture and how aperture is calculated, but how using aperture affects your photography. Aperture is one of the most important components to photography, so its essential to have an understanding of how aperture works and how to know what to set your aperture to! Ready? Lets dive in.

Common questions people ask about aperture:

Why does aperture affect depth of field?

Simply put, the aperture of a lens is the size of the hole allowing light to pass through to the camera. The larger the hole, the greater the angle of light entering the camera, which results in a shallower depth of field. For an in depth explanation, watch our video explanation of aperture and depth of field!

Is aperture the same as f-stop?

No. Aperture is technically the diameter of your lens opening that allows light into the camera. But aperture is commonly incorrectly referred to when talking about a lenses f-stop, which is a measurement of how much light a lens funnels into the camera. F stops are calculated by dividing a lenses focal length by its aperture. To make this less confusing, check out our video which explains the differences between aperture and fstops.

Why are lenses called “fast”?

A lens with a larger aperture lets more light into the camera. Lenses with larger apertures are called fast because this allows the photographer to use a higher (faster) shutter speed!

What is the theoretical fastest lens possible?

There is no theoretical limit to the aperture of a lens or the fastest possible lens stop. It is only limited by the practicalities of size, weight and cost to produce such large, heavy and impractical lenses! The fastest lens ever made was f0.33, and was made for show purposes only as it was ridiculously heavy and impractical.

Why is a lower f-stop better?

A lower f-stop means more light enters the camera, which makes it easier to expose your image without having to compensate with higher iso or a slower shutter speed which risks motion blur.

What is an iris?

On a camera, the iris is the mechanical device inside the lens that expands and contracts to enlarge and shrink the size of the lens opening. This determines the aperture of the lens and the amount of light that reaches the camera.

What does the f in f-stop stand for?

The f in f-stop stands for focal length – Which is the length of the lens barrel, measured in millimetres.

How is aperture calculated?

Aperture is calculated by measuring the diameter of the lens opening. The fstop of that lens is then calculated by dividing the focal length by the length of the aperture.


[powerkit_collapsible title=”>TRANSCRIPT<“]
one of the most confusing pieces of
photography to understand is aperture
what does it mean when a lens has an
aperture of f/4 or f/8 what does it mean
when my aperture is wide open or when
it’s closed down why does that affect my
depth of field and what is depth of
field the list goes on but if you want
to get the most out of your photos you
have to have an understanding of how
aperture works and how to apply it to
your photography so today we are going
to be diving into one of the most
confusing and misunderstood topics of
all of photography and that is aperture
we’re going to unpack what it means and
how it applies to your photos how you
can use aperture and understand it
easily simply without the technical
jargon let’s get to it
all right so let’s make this as simple
and basic as possible aperture if you
look up the technical definition is just
an opening that light comes through so
what does that mean for us photographers
it means that aperture the aperture of
your lens is the hole that lets light go
through this lens out the other side to
your camera you follow me so the size of
that hole actually changes and that’s
done by a little mechanical thing inside
of your lens that opens and closes and
changes the size of that hole so it’s
changing the size of the aperture that
is called the iris so I have this
vintage lens here and I’m going to just
hold it up to the camera and show you
what I mean the aperture is the hole
through which you’re seeing light so I
can hold it up to this camera and you
can see it getting larger and smaller
well it’s getting larger and smaller
because I am actually adjusting the iris
so when you stop down or stop up change
the f-number of your lens and we will
talk about what that means in a second
the hole is getting larger and smaller
because of the iris okay so we have that
technical definition out of the way
aperture is just the size of the hole in
the camera and that’s changed by the
iris right well the next thing that we
have to ask is what does it mean when a
lens is f/4 f8 or f-16 or F 1.4 what do
those numbers mean and how does that
have anything to do with aperture great
question so the F number of a lens is
also known as the f-stop the F stands
for focal length and focal length is
just the length of the lens how long it
is in millimeters you got it now we take
the focal length and we divide it by the
aperture which again is the size of that
hole measured in millimeters across and
we get our f-stop number so if you have
a 35 millimeter lens an 85 a 50
millimeter a 7200 those are all the
length of the actual barrel of the lens
if you take these two numbers and you
divide them that’s how you get that
number that comes after the F whether
it’s f4 f6 f8 so let’s look at a quick
example this will start to make sense
just track with me for another second ok
so this is a 50 millimeter lens so
obviously it’s 50 millimeters long
that’s the focal length now if the
aperture we took a measuring tape and we
measured that hole in the lens and it
happened to be 36 millimeters if we
actually divide this out you would get
1.4 so this particular lens at this
particular aperture setting would happen
to be f
point four that’s where that number
comes from and typically when you
actually look at the speed of a lens
what’s known as the speed of a lens is
just the maximum width of this number
down here the maximum width at that hole
opens up to let light in so here’s the
question that you should be asking why
does this actually matter Ryan so this
is actually super helpful to us as
photographers because it lets us compare
the brightness of different lenses even
if they have completely different focal
lengths so let me give you an example of
this let’s say that I were to go and get
a bunch of different food I got a pizza
an ice cream cone a steak and and donut
right they all have very different
qualities completely different foods but
what do we do we compare the calories
now technically a calorie is the
calculation of the amount of energy
needed to raise the temperature of a
kilogram of water by one degree Celsius
not practically does that matter to us
no but because they’ve come up with this
equation it allows us to compare the
energy value of food from one completely
different food to another now that’s
what aperture does let’s say I’ve got my
camera out in the park and I’m taking a
walk and I see a bear so I pull out my
camera and I take a photograph using my
70 millimeter zoom lens so I’ve got it
set at 70 millimeters and it’s f 2.8
because I want to get nice and close to
that bear now let’s say 30 seconds later
that bear starts running towards me and
I’m too stupid to run away so I say oh
shoot I can’t fit the bear in my frame
anymore I have to switch to my 35
millimeter I wonder what settings I
should set my camera to now as long as I
set my 35 millimeter lens to the same
aperture as I had my 70 millimeter lens
my shot will still be exposed properly
without changing any of my camera
settings super handy right so as long as
my aperture stays the same I don’t have
to change any of my camera settings see
how handy that is so the real question
is now that we kind of know what
aperture is and where those numbers come
from how do we actually apply this into
our photography and how do we understand
where to set that number how do we get
our mind kind of around what f/4 means
and f-16 means and what that all does
what it comes down to is when you look
at that equation it winds up meaning
this the higher that F number becomes
the smaller your aperture must be now
this matters because obviously the
smaller the hole gets the less light
that is going to go through that lens
and the less light that goes through
that lens the darker it’s going to be
and so it’s going to be hard
to get a well exposed image now what is
well exposed mean let’s say I’m taking a
photo of a bear and it’s 9 o’clock at
night and I take the photo and it looks
like this not very helpful right that’s
not well exposed but if I take a photo
of the bear and I can see everything I
want to see that’s a well exposed image
so if I don’t have much light coming
into my lens its way harder to do that
because all I can do to make that image
better expose is decrease my shutter
speed in which case if the bear is
charging at me it’s going to be totally
blurry or I can increase my ISO and the
higher the ISO goes the more grainy and
mushy and just kind of gross looking so
obviously we don’t want this when we’re
in a low-light environment that’s why
you really want a lens that has an
aperture that is very wide it’s a big
hole it lets a lot of light into the
lens and it’s easier to get well exposed
images now the thing that gets a little
bit confusing about that is obviously
the higher the f-number the smaller the
aperture it’s backwards of what you
would expect I’ve got an easy way to
remember this okay here’s the make sense
definition pretend that the F stands for
number of foxes all right bear with me
for a second let’s say that you are
fighting foxes in the park and the bear
has left you’re fighting foxes now and
there’s one Fox at first and you can see
pretty well but let’s say that 15,000
foxes come and they’re in one giant fox
herd and they’re all in front of you and
you can’t see anything and it just gets
dark because the foxes are blotting out
the sky that’s how dark it is there’s
that many foxes that Fox number
increasing is going to get darker and
darker and darker until we can’t see
anything and the park is just one big
black mess now let’s say that someone
fires a gun it’s an anti Fox repellent
and the foxes start running out of the
way they’re lowering the f-number is
going down down down down down and the
lower that f-number gets the less foxes
there are the brighter everything
becomes because all of a sudden we can
see the sky we can see the trees and we
can start taking photos again because we
can see what we’re doing now obviously
because the less light you let into your
lens the harder it’s going to be to get
a well exposed image the question you
then ask is should I then just leave my
aperture as wide open as possible all of
the time and the answer is no why
aperture does something else other than
just kind of determine how much light
gets into the lens it also determines
something called depth of field now what
is depth of field well we could be
technical about it and talk
about how much of the image is in focus
but really look at this image see how
blurry it is in the background that’s
depth of field so if you have a very
shallow depth of field that means that
up here where you can’t see in the image
up front up close it would be in focus
but the background is super super
out-of-focus because the depth of field
the amount of that image that’s in focus
is very shallow now if that explanation
didn’t make sense let me show you in a
chart because everyone loves charts
let’s say you’re here and you’ve got
your camera and you’re looking just hot
stuff right and we’re set up in the
local park and you’re looking and BAM a
bison comes into view it’s wow what a
majestic bison I should take a photo of
that bison and then you see oh there’s a
fox and the Bison is chasing the Fox and
then you say wait no the Bison is
chasing the Fox which is chasing a duck
great we want to take a photo of all of
this if we want to take a photo of all
of these things which are spread out
from five feet away to you to 25 feet
away from you you’re going to need a
very wide depth of field you’re going to
need a lot of your image to be in focus
so you’re going to determine what your
aperture is set to based around that
because this is how aperture works in
depth of field so let’s pretend we have
a lens here with an aperture of f12 that
means the aperture is wide open that
hole is really big letting lots of light
in now we’re not going to explain in
this video exactly how focusing works on
a lens but suffice it to say the way
that a lens focuses light is it grabs
light and takes it down to one
particular point that all becomes in
focus now that one point is symbolized
by these converging lines here that’s
the in focus portion of this image and
this particular lens diagram it’s set to
about 12 feet
that’s where everything comes into focus
now on either side you see these red
lines those are the points in the image
that are still pretty sharp so they’re
not as sharp as this one point here that
is completely in focus but they’re still
visibly to your eye they look like more
or less they’re in focus that’s called
your depth of field from this far point
here that’s still pretty sharp to this
closer point here that is still
reasonably sharp all right everything
that falls outside of these two lines is
considered to be out of focus when you
look at it with your eye it looks a
little bit blurry whether it’s closer
towards you like our friend here mr.
bison or farther away like friend here
mr. duck now that’s with an aperture of
f12 now let’s say that I actually took
my aperture and I said it smaller so I
closed it down and I set it to say f-16
now because we’re using an aperture of
f/16 you can see the light actually
entering this lens is doing so at a much
shallower angle compared to our F 1.2
lens look at that angle compared to this
angle and therefore the point that gets
resolved the point that’s in focus in
our lens and the acceptable in focus
distance is quite a bit broader you can
see that now mr. bison and mr. duck are
somewhat in focus now if we stopped it
down even further to say F 32 this would
be even increased again and probably our
whole mr. bison and whole mr. duck would
also be in focus so that’s how we would
determine whether or not we want to use
something like f 1.2 or f-16 how much of
the image do we actually need to get in
focus if we just want the focus to be on
our Fox and have everything else made
blurry then we would do something like f
1.2 if however we want to capture our
entire scene then we would do something
a little bit more like f-16 where we
have a much much broader depth of field
and so you can see that the way you set
your aperture and the settings you
choose really depends on what you want
to get out of that specific situation
for instance with this portrait shoot we
wanted to separate this couple from the
background so you can see just how
out-of-focus the background is because
our aperture was wide wide open and we
were using a tighter lens however in
this photo over here you could see that
everything in this photo is in focus and
that’s a good thing you don’t want to
have all of the background out of focus
when the background is kind of part of
the image and you’re showing that off so
it really depends on what you want to
get out of the situation so if we’re
going to recap absolutely everything in
10 seconds aperture is the hole in your
lens this is controlled by the iris
which is that metal thingy that changes
the size of the hole in your lens the F
numbers what do they stand for the
f-stop is a measurement of how much
light reaches the lens by dividing the
focal length of that lens by the
aperture the width of its opening this
matters because it gives us a rough
number where we can actually compare
brightnesses across different lenses of
different focal lengths and so what that
all comes down to is the higher that F
number is the smaller the aperture it’s
a little backwards so the way to
remember that is basically pretending
that F stands for a number of foxes
standing in front of your camera you add
foxes you’re going to get less light in
your camera and so it’s going to get
darker you take away foxes you reduce
that F number the lower it is you have
more light coming into your camera so
are brighter now does aperture do
anything else other than just let light
in yes it increases and decreases the
depth of field depending on what you set
your aperture to so the lower that
f-number the shallower your depth of
field the more out-of-focus everything
else is going to become this happens
because of the actual mechanics behind a
lens and the angle of light coming into
the lens so in the end the actual
correct aperture for any given image is
going to depend on what you want out of
that photo do you want the entire
background and everything in that photo
to be in focus use a high aperture f/8
f-16 whereas if you want to really blow
out the background have it super soft
out-of-focus and dreamy just to place
more emphasis on your subjects well then
you want to use a lower aperture
something like f 1.4 F 2.8 and most of
the time as a general rule you want to
have your aperture as wide as you can to
maximize the amount of light coming into
that camera so that your image quality
is better and that out-of-focus look
does tend to add more emphasis on your
photos so as we go through here and we
look you can see that this was with F
1.4 F 4 F 1.8 in general you’ll find
that most of the time we are shooting
with lower apertures and that’s why
lenses that have lower apertures are
more expensive they let more light into
the camera and they also produce those
really out-of-focus backgrounds so that
is aperture in a nutshell whoo so there
you have it everything you ever wanted
to know about aperture and probably a
little bit more if this video was
helpful please make sure to hit that
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