Aperture

THE MOST CREATIVE COMPONENT OF EXPOSURE

APERTURE in a nutshell

Scroll down for a very detailled description.

what is the aperture?

Aperture is a pretty sophisticated term for a hole in the lens of your camera. That hole can be made bigger or smaller.
As mundane as that may sound, the effect that hole has on your images is massive.

The effects of aperture

1. Image brightness (Exposure)

Easier to understand, but less creative than the other, is the effect of the aperture setting on image brightness.

Quite logically, when you make an opening bigger, it will let more light in. What is familiar from the blinds of a window, curtains, etc., is the same with the aperture.

The more you open it, the more light you let in.

HOW BIG THAT EFFECT IS MAY SURPRISE SOME OF YOU

small aperture:
less light

This image shows the maximum aperture opening of most “kit lenses” – which is f/5.6 ( If you’re interested, I’ll explain what aperture numbers mean down below).
The hole in the middle is pretty small, and that means  that most of the light is blocked by the aperture.

Aperture f/5.6
Lens with aperture opening of f/5.6

large aperture:
more light

This is not a kit-lens though, but a so-called prime lens. Some of them can be had for very little money (read about the famous nift-fifty).
Prime lenses have much bigger maximum aperture openings than zoom lenses. In this image I opened this lens for example to f/2 instead.
Look at how much bigger the opening is compared to the f/5.6 above!

Aperture f/2
Lens with aperture opening of f/2
twice
  • the size
  • the brightness

This image shows the the size difference of the first opening (f/5.6) in red, overlaid on the bigger opening (f/2).

The amount of light that can enter the camera through the aperture is directly related to the size of the opening. If it is twice the size, you get twice the image brightness.

Here it is
  • 8x
  • 8x
bigger

So a rather cheap prime lens, like the nifty-fifty will give you 8 times more light than the kit lens. You’ll soon find out how valuable that can be.

Aperture f/2 with overlay of aperture f/5.6
Lens with an aperture opening of f/2 and a graphical overlay of f/5.6

Do you remember that doubling of light?

When I introduced you to scene luminance, I said one EV will double the brightness. One EV was equal to one stop.
I told you that the doubling of brightness is pretty important in photography, and here it appears for the second time. Twice the area of the aperture opening, twice the brightness, which also means one stop brighter, or again one EV brighter.

I bet you start understanding the importance of Exposure Values (EV) in photography.

The images below show the aperture opening increase 2x in size in each image

sample shot of aperture set to f/16
aperture symbol f/16

Aperture f/16

sample shot of aperture set to f/11
aperture symbol f/11

Aperture f/11

sample shot of aperture set to f/8
aperture symbol f/8

Aperture f/8

sample shot of aperture set to f/5.6
aperture symbol f/5.6

Aperture f/5.6

sample shot of aperture set to f/4
aperture symbol f/4

Aperture f/4

sample shot of aperture set to f/2.8
aperture symbol f/2.8

Aperture f/2.8

sample shot of aperture set to f/2
aperture symbol f/2

Aperture f/2

sample shot of aperture set to f/1.4
aperture symbol f/1.4

Aperture f/1.4

As you can see, by doubling the size of the aperture opening, the image brightness doubles too.

testing

width 100%:

width 900px:

I hope you see the pattern when you compare it to scene luminance, where every exposure value doubles the brightness.

But why are there some increments in between?
The aperture chart has some additional increments compared to the scene luminance chart.
Rather than only giving you the chance to double or half the brightness of your images, camera manufacturers give you the option to much finer adjust the brightness. The increments in between are 1/3 stops. Usually the custom settings in your camera let you choose between 1/3 stops and 1/2 stops. I’d recommend 1/3 stops.

aperture full and third stops

Full Stop

f/8 f/11

1/3 Stop

f/8 f/9

In case you now try that with your camera and you don’t see any changes in your images when you change the aperture on your camera:
In any auto or semi-auto mode (Auto, P, Tv, Av, S, A,…), the camera will compensate for the loss of light, by adjusting another setting. Only if you change to manual exposure (M), will you see the direct effect that changing aperture has on image brightness.

The effects of aperture

2. Depth of focus

Beside the very important effect on image brightness, the aperture has a much more exciting effect on images. It changes what photographers call depth of field. Personally I like to call it depth of focus. There is a slight difference between these two terms for tech nerds, but in practical use, they are 100% the same.

Depth of focus actually has two effects. Let me show them one by one

2.1 BACKGROUND BLUR

I won’t write too much, but rather let images speak.

aperture symbol f/16

Aperture f/16

aperture symbol f/11

Aperture f/11

aperture symbol f/8

Aperture f/8

aperture symbol f/5.6

Aperture f/5.6

aperture symbol f/4

Aperture f/4

aperture symbol f/2.8

Aperture f/2.8

aperture symbol f/2

Aperture f/2

aperture symbol f/1.4

Aperture f/1.4

Personally, I just love the blurred backgrounds, that low aperture-numbers give me. The difference is massive, and it helps separate your subject from the background, particularly in portraits.

Do you wonder why the images above all have the same brightness?
We just learned that changing the aperture will change the image brightness, so how is it possible that I changed the aperture numbers and the brightness stayed the same?
Remember, the aperture is just one of the settings that has an influence on image brightness. Of course I wanted all these images to have the same brightness, so I compensated (in so-called aperture priority the camera would automatically do that) for the loss of light, by changing another setting, which you will learn in a second.

Why the question mark at f/1.4?
To make you aware that not every lens supports such low aperture-numbers. Kit lenses usually stop at f/5.6 for portraits like this. Let me show you the difference in background blur between using a kit lens at f/5.6 vs a prime lens.

f/1.8 f/5.6

If you are now hooked and want to know more about background blur, here is the link to my youtube video: The 5 Factors of Background Blur.

BTW: if you now consider upgrading your lens, every manufacturer has a rather affordable 50mm f/1.8 lens, the so-called Nifty Fifty – read more about that here: What is a Nifty Fifty?

2.2 BIGGER AREA OF FOCUS

If you have another look at the images above, you see that the area that is in focus has decreased the lower the f-number. That is an advantage in portraits, because it helps separate your subject from the background, but it can also be a disadvantage.

Again, I want to let images speak for themselves.

aperture symbol f/32

Aperture f/32

aperture symbol f/22

Aperture f/22

aperture symbol f/16

Aperture f/16

aperture symbol f/11

Aperture f/11

aperture symbol f/8

Aperture f/8

aperture symbol f/5.6

Aperture f/5.6

aperture symbol f/4

Aperture f/4

aperture symbol f/2.8

Aperture f/2.8

For example in macro photography or product photography, you often want as much of your image sharp as possible. In these cases, low aperture-numbers don’t make sense and you want to raise them to get more of your image sharp.
Why the red question mark (this time in the first image at the highest aperture-number)?
To make you aware that not every lens supports the higher numbers either, and also make you aware that f-numbers don’t stop at f/16, like in the portrait example. Many lenses will go up to f/32, very few even higher. Click the question mark to see the image shot at an aperture of f/32. The lineup above is a typical example of the aperture range of a dedicated macro lens, which often ranges from f/2.8 to f/32.
In the advanced section below, I will tell you why it might not be the best idea to use very high numbers, even though the big depth of focus seems like a blessing at times.
Below is a direct comparison between the depth of focus you get when shoot at the lowest and highest aperture-numbers of a macro lens.
f/2.8 f/32

THE APERTURE RANGE IS LIMITED

Now that you learned that aperture has a limited amount of settings to choose from, it is important to have another look at it’s effect on image brightness.
While you see that doubling of the aperture opening has quite a big influence on your images, you also see that the range is limited.

Aperture range of "kit lenses"

Kit lenses usually have a range between f/5.6 – f/32, which is a range of 5 stops.

aperture range kit lens

Aperture range of macro lenses

Typical macro lenses on the other hand, range from f/2.8 – f/32, which is a range of 7 stops.
For macro you usually want a higher depth of focus, that’s why these lenses emphasize the higher f-numbers.

aperture range macro lens

Aperture range of portrait lenses

Professional portrait lenses often have an aperture range from f/1.4 to f/16, which again is 7 stops
For portraits photographers often want a blurred background, so the aperture range emphasizes the lower f-numbers.

aperture range kit lens

Compare aperture range to scene luminance

But if you compare the amount of aperture stops in various lenses to the possible stops that scene luminance has, you realize that the influence of aperture on image brightness is far less than that of scene luminance.

exposure value graphic for scene luminance

So you learn two things:

  • Scene Luminance has a much bigger influence on image brightness than aperture has and that's one of the reasons why it is the most important component of exposure, despite not being listed in the exposure triangle.
  • Because of that smaller range compared to the huge range that scene luminance has, you cannot control image brightness with aperture alone

APERTURE MNEMONIC

Bigger aperture number (f-number)
More light is blocked
Bigger depth of focus

Aperture FAQ

Here is a list about the most frequently asked questions regarding aperture

That depends mostly on your lens, but also on the number of people in the group. Don’t listen to people who tell you, that you need to choose the number according to the number of people. That’s just plain wrong.

There are apps available that let you calculate the depth of field (or depth of focus as I like to call it). The most popular one is PhotoPills. But there are also online calculators available.

Please comment below. I will constantly update this section with new questions.

If you are a photography beginner, skip this section and continue to shutter speed above.
Return, once you feel comfortable to learn more about the aperture.

Advanced aperterture knowledge

the nerdy stuff

If you are a photography beginner, skip this section and continue to shutter speed above.
Return, once you feel comfortable to learn more about the aperture.

WHAT DO APERTURE NUMBERS STAND FOR?

AND WHAT IS f/?

aperture symbol f/5.6
F/ 0
aperture symbol f/4
F/ 0
aperture symbol f/2.8
F/ 0
aperture symbol f/2
F/ 0
aperture symbol f/1.4
F/ 0

f-numbers make sense

The aperture number shows how big the diameter of the aperture opening is, relative to the focal length. If you don’t know what focal length is – for example your kit-lens has a focal length of 18-55mm (it’s variable, because you can zoom – if you fully zoom in, your focal length is 55mm, if you fully zoom out, it’s 18mm).

So “f” stands for focal length, f/2 stands for 1/2 the focal length.

aperture formula for f/2

Easy example: focal length f=100mm

If you use lens with a focal length of 100mm, f/2 would mean that the diameter of the aperture is 50mm

aperture calculation example for f=100mm

size matters

Remember, I said the size of the area of the opening, so the size of the hole is what matters.

From school we know that the formula for the area of the circle  is r-square.𝝅.

r stands for radius, which is half the diameter. So r=d/2

aperture size formula

2x size for every stop

If we now use that formula to calculate the area of the aperture opening, we get roughly twice the size of f/2 compared to f/2.8.
Why roughly?
Well, the aperture row actually starts with f/1, and the f-number that would represent the exact half the size of f/1, would not be f/1.4, as it is usually listed, but rather f/1.414213… – which btw. is the square root of 2.
So f/2.8 is not really f/2.8, but rather f/2.82842…
But I think f/2.8 is already complicated enough 😅.

aperture calculation for various sizes

Now you should understand why the aperture numbers are so weird, what f/ is and why the size doubles with every stop. BTW: I also have a video about the calculation of aperture numbers.

WHICH APERTURE-SETTING
CREATES THE SHARPEST IMAGES?

for half-nerds

Small f-numbers create softer images

For non-nerds, here is the fast explanation: Small f-numbers usually create softer images. That’s why some photographers don’t recommend shooting a lens at it’s smallest f-number (using the smallest f-number is usually called “shooting wide open”).
However, that is not valid for all lenses. Professional lenses of newer generations (for example the Sigma Art lens series), create stunningly sharp images, even wide open. However, using bigger f-numbers will still even create slightly sharper images.
The higher the quality of a lens (usually that’s a question of your budget), the sharper it is wide open, compared to using higher f-numbers.

High f-numbers create softer images

Sounds weird, but the same is true for the other end of the scale. The highest f-numbers of a lens also create softer images due to an effect called diffraction, that I will explain in detail in the nerdy part down below – just continue reading!

Where is the physical sweet-spot?

In general the sweet-spot for the aperture with the sharpest overall image is usually somewhere around f/8 to f/11. But that not only varies among different lens models, but also among lenses of the same model. All you can do is make test shots with your own lens and find out which one is the best setting for your lens.

Where is the subjective sweet-spot?

The specific sweet spot for an image can of course differ from the physical sweet-spot of a lens. Let’s consider you need a very high depth of focus (DOF). You would then sacrifice the overall sharpness, for a wider depth of focus and therefore the sweet-spot for that particular image, would be higher than the objective sweet-spot of that lens.

well exposed image
f/16 for bigger depth of focus

And the same is true for the other end of the scale. If you are shooting something and your goal is to separate your subject as good as possible from the background, you want a very shallow depth. That doesn’t necessarily have to be a portrait.
To achieve that, you might be willing to sacrifice sharpness over separation. I like to call that perceived sharpness because the image sometimes looks sharper, because the subject stands out so well in front of the rest of the image, that is blurry.

dog small aperture number
f/1.8 for maximum background blur

So always using the sharpest setting of your lens, isn’t very clever. But for scenes like a regular landscape, it is good to know where it is.

WHICH APERTURE-SETTING
CREATES THE SHARPEST IMAGES?

for complete nerds

Why does a lower f-number create softer images?

For those of you who wonder why a lower aperture-number creates softer images, that has to do with an effect called spheric aberration.
In a perfect lens, all incoming light rays, are focused in one single focus point.

Here is a very basic graph to illustrate that, think of starting a fire with a magnifying glass, in an ideal lens, the sun would create a very very tiny spot, where all the sunlight is concentrated:

The reality however is: lenses aren’t perfect – particularly not the cheaper lenses that come with most cameras, and also not zoom-lenses. Because lenses need to be very well “calibrated” (it’s actually more than that, but that would lead too far) and the manufacturers can only “calibrate” lenses for a certain focal length. Not over a very wide range of focal lengths, like for example in an 18-400mm lens.
That’s why prime lenses are usually sharper than similar priced (or even more expensive) zoom lenses.

So: lenses are hardly ever perfect and have so-called lens errors.

Spheric aberration

One of these lens errors is spheric aberration. In less than perfect lenses, the incoming light rays are not focused in one single focus point, but some rather in front of the sensor plane (which btw. is the plane where you want the rays to be focused), some right at the sensor plane and others behind.

Here is basic graph again. Instead of focusing the light rays to a single point, they are all over the place. The more these rays deviate, the less sharp the lens is.

Aspheric lens elements.

As you can see in the graph above, it’s mostly the rays at the edge of the lens that cause the problem. There are two ways to solve the issue. The first, more difficult and more expensive way is, correcting the edge of the lens for that error and try to refract the rays into the center. To do that, lens manufacturers produce so-called aspherical glass elements, so glass that is not “round” (hence spheric) on the surface, but rather flattens out towards the edge. That will grab the light rays and refract them further away from the glass.
The result is a sharper image.

As you can see, they are still not perfectly focused. Particularly newer generation professional lenses have become pretty close to the perfection. But they are still not there yet.
The more technology advances, the better the lenses have become. So don’t trust anyone who says old lenses are sharper. If you compare lenses of the same class (so new pro lenses to old pro lenses, the old ones don’t stand a chance).

However, we still don’t have a perfectly sharp image. So what can we do to further improve the sharpness?

Reducing the aperture opening to enhance sharpness.

Why did I tell you all of the above? It doesn’t seem to have anything to do with aperture. Oh yes it does, and here is why.

We see that it’s still the outer rays that cause trouble. What if we could get rid of those outer rays and only keep the ones that are perfectly focused?

That’s where the aperture enters the stage. By closing the aperture, you literally cut away the rays that enter the glass at the edge of the frame, so all that is left are the inner rays, that are much better focused to a single spot.

 

So our high quality glass, that was pretty sharp to begin with, got even sharper by closing the aperture.

But that is also one of the reasons why cheaper lenses don’t have low aperture numbers, but rather start with f/5.6 instead of f/1.4. It’s simply much cheaper to only cut away the rays that are causing trouble, than refract them by creating high quality and perfectly shaped glass.

However, of course quality lenses are also better in regard to focussing the inner rays, and that’s why they maintain their advantage over cheaper glass, even when closing the aperture. The gap gets closer though.

The image gets sharper and sharper until it reaches a certain sweet-spot. But what happens after that sweet-spot.

Diffraction

Closing the aperture, doesn’t only have positive effects, there is also a negative one.
On sharp edges, rays and waves are being deviated. Aperture blades represent such a sharp edge, and that gets us into trouble.

With open apertures, that isn’t an issue, because most of the rays are deviated outside the sensor area and beside that, there are more rays coming through the big opening, kinda ovderpowering the deviated rays that are caused by diffraction. But closing the aperture not only brings the rays right onto the camera sensor, but also reduced amount of light from rays that are passing the opening without being deviated makes them more prominent. The result is an increasing amount of blur, the more you close the aperture

Where is the sweet spot?

Somewhere between the cutting away of the edge rays and the kicking in of diffraction is the aperture setting that produces the least amount of blur or better said the sharpest image.
That sweet spot is different for every lens. To find it, you have to do some test shots with every aperture setting. Usually it is around f/8-f/11.

Disclaimer: the above explanations and graphs are very simplified and not made for scientific purposes. They are rather meant to help you understand and learn photography.

ADDITIONAL EFFECTS OF APERTURE

Reduction of vignetting

Remember smaller apertures cutting light that enters the edge of a lens? When shooting wide open, the outer rays are usually darker. Stopping down will reduce that effect and produce a more evenly lit frame.
Also when using filters on ultra wide-angle lenses, that can help quite a bit, because the thread of some filters (unless they are slim) will appear in the frame. Stopping down will remove that to some extent.

Reduction of Chromatic Aberration

Chromatic aberration is similar to spheric aberration. It is mostly visible in the corners of a frame and particularly in areas with high contrasts. It is usually more prominent in cheaper lenses, but you can get it in any lens, depending on the conditions.
Stopping down can dramatically reduce chromatic aberration, but you can also reduce it using your editing software.

BOKEH AND STAR SHAPES

Very closely related to the aperture is the so-called bokeh – see the definition of bokeh on wikipedia.

The rounder the aperture opening, the more pleasing and rounder are blurred highlights rendered – usually desirable for example in blurred portrait backgrounds. Rounder openings are usually created by more aperture blades as well as special shapes and blade-placement during the closing process. So bokeh has a lot to do with aperture.

So do stars that are created for example in night shots of cityscapes when using rather high f-numbers. Depending on the shape of the opening and the number of blades, the stars are more or less pronounced and have more or less rays. Here is an example of a christmas Tree image shot with a kit lens that has six blades, vs an image shot with a

stars created by aperture settings 6 blades
christmas tree stars created by aperture settings 6 blades
stars created by aperture settings 9 blades
Christmas tree stars created by aperture settings 9 blades

Do you want to shoot images like these?

These images were all shot by me. My name is Wolf Amri, I’m a professional photographer and film maker.

On my youtube channel, I explain not only exposure, but everything else you need to know about photography. Explaining in a video is much easier than written because I can show you images, animations and examples on the way. So let me recommend watching my youtube beginner photography course.

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