What Is Aperture In Photography? Hi and welcome to Episode 155 of the Photography Explained podcast. I’m your host Rick, and in each episode, I will try to explain one photographic thing to you in plain English, in less than 27 minutes (ish), without the irrelevant details. What I tell you is based on my lifetime of photographic experience. And not Google. Ok, there was some Google research in this one. Thank you, Google.
First – here is the answery bit
Aperture in photography is the size of the opening in the camera lens which light passes through to get to the camera sensor. The aperture can be made larger to let more light in, or smaller to let less light in. The aperture is used in conjunction with the camera shutter speed to get the correct exposure. The aperture is also used in conjunction with shutter speed and ISO to take photos with different camera settings. The aperture used also determines the depth of field in an image, which is the amount that is sharp from front to back.
So yes, the aperture determines how much light gets through to the camera sensor. So it is important.
That was the answery bit. Here is the talky bit. And a good answer it was too. If I say so myself.
You can listen to the episode here
Or keep on reading. Or both – up to you!
This is what I said in episode 154 which was all about getting the correct exposure every time you take a photo.
“The aperture is the opening in the camera lens that lets the light through to the camera sensor when you take a photo. Larger aperture, the smaller number, more light gets in. Smaller aperture, larger number, less light gets in. I know.”
The aperture is one of the three components of the exposure triangle, along with shutter speed and ISO.
OK – some stuff for me to explain then.
Maximum aperture
When you buy a camera lens it is described like this – let’s use my favourite lens, the Canon EF 17-40mm f/4L USM. This is how it is listed on the Canon website. It is also called a 17-40 mm lens for short. Well by me anyway.
17 is the widest focal length, which is actually 17mm
40 is the narrowest focal length, 40mm
f/4 is the maximum aperture
And for completeness,
L tells you that this is from the professional lens range. L actually stands for luxury. Probably. But that is not important here.
USM is Ultra Sonic Motor, again not important here.
So the f4 is the maximum aperture. This is the full opening in the lens, with the aperture fully open. This lets in the maximum amount of light, allowing you to use a faster shutter speed. This aperture setting also has the least depth of field.
Why is this so important?
Simple. The smaller the number, the larger the maximum aperture, the faster the lens is. This is important as the larger the maximum aperture is, the more light gets through to the sensor. And that means that you can use a faster shutter speed, or take photos in lower light levels handheld. A camera lens with a large maximum aperture is known as a fast lens, fast as in relative to a camera lens with a smaller maximum aperture. And in general terms, the larger the maximum aperture, the larger, heavier and more expensive the lens is.
- Large aperture – more light
- Small aperture – less light
Minimum aperture
At the other end of the aperture scale is the minimum aperture. The minimum aperture is the largest number, but with the smallest aperture, letting the least amount of light through to the camera lens.
- On my Canon 17-40mm lens the minimum aperture is F22.
What do these numbers mean?
- f/4 – wide aperture letting the most light in
- f/22 – small aperture letting the least light in
Counterintuitive right? But there is a simple explanation for this.
Let me go through the aperture scale first
- f/1.8, f/2.8, f/4/0, f/5.6, f/8.0, f/11, f/16, f/22, f/32, f/64
These are full stops. A full stop is a doubling or a halving of the light. More on that in a minute. But what do the numbers actually mean? And I know I am in danger of going into irrelevant detail here, but let’s give this a go.
Well, first off f/4 is called the f-stop. It is also called f-number with a dash, f number without a dash. And it is also called aperture value. And f-stop value. I know, I know.
Written correctly, it is small f, / forward slash and then the number. And that gives us a clue.
The f stands for focal length, and the number is a fraction of the focal length. Do I need to go into any more detail? No, I do not. I am happy with the fact that the f-stop is a fraction of something, which makes the large number for a small opening and the small number for a large opening almost make sense. The actual aperture size is not important. Let’s move on.
What these numbers actually mean
If you go from f/5.6 to f/8, you are halving the amount of light that gets through to the camera sensor. And if you go from f/11 to f/8 you are doubling the amount of light that gets through to the camera sensor.
And this is directly related to shutter speed – change the shutter speed from 1/250th second to 1/125th second and you are doubling the amount of light that gets through to the camera sensor.
- Both changes are of 1 stop.
And this is the important bit.
You are going to take a photo, and the camera is saying that the correct exposure is1/250th second at f/8. You want to change the aperture, to say f/11. f/8 to f/11 is 1 stop. You have halved the amount of light getting through to the camera sensor. If you take the photo using 1/250th second at f/11 your photo will be underexposed, it will be too dark, and you will not have captured the range of light correctly.
So what you need to do is to change the shutter speed by one stop, going from 1/250th second to 1/125th second. The shutter is open for double the amount of time, doubling the amount of light.
And this is how we can change this stuff, and how closely related and important aperture and shutter speed are in photography. So much so that I will cover shutter speed next, then ISO, and then the exposure triangle.
I want to get back to aperture though, and tell you some other stuff that you need to know.
How to see your aperture
This is an audio explanation of aperture – check out images of the camera aperture on the blog post for this episode and you can see what I am talking about. Here it is.
Source – Canon US website – https://www.usa.canon.com/learning/training-articles/training-articles-list/what-is-aperture
But if you have a depth of field preview button select the minimum aperture on your lens and press the depth of field preview button and you should be able to see your aperture.
Do this and you can see what a wider aperture and a narrower aperture look like. You can change the size of the aperture, which helps to make sense of the more light / less light thing.
Depth of field
Seamlessly moving on to depth of field, smooth eh?
The aperture selected determines the depth of field of an image. I like to describe the depth of field as the amount of a photo that is sharp from front to back.
- Use the maximum aperture and you get the least depth of field
- Use the minimum aperture and you get the most depth of field
- Larger apertures give less depth of field
- Smaller apertures give more depth of field
- If you were photographing say a person and you wanted a blurred background you would use a smaller aperture.
- If you were photographing a landscape and wanted everything to be in sharp focus you would use a smaller aperture.
The depth of field varies with the focal length that you use, I get more depth of field at 17mm than I do at 40mm.
I will do an episode on depth of field in a future episode, currently though this is scheduled for December 23!
Lens errors and the lens sweet spot
Every camera lens has what we call the sweet spot, where the aperture selected gives the sharpest image with the least optical errors. This is normally somewhere in the middle of the aperture scale for a camera. On my Canon 17-40mm lens it is f/8.
Shoot with the maximum aperture and you can get problems with diffraction, as you are shoehorning the light through a small opening in effect. Shoot with a maximum aperture and you can get bits that are not sharp. But somewhere in the middle is the sweet spot, the best aperture providing the highest quality image capture.
Aperture and different types of camera
Now then. This is one that I am going to mention quickly and move on. There are three main types of consumer cameras, full frame, cropped sensor and micro four thirds. Each of these has different sensor sizes. And I am talking here about digital cameras, DSLRs and mirrorless cameras. Well, micro four thirds cameras are mirrorless cameras full stop. Oh no did I say full stop?
Different camera systems
Is f/8 the same on all of these different camera systems? No. In general terms, the larger the camera sensor, the less the depth of field. But this is balanced by using wider focal lengths. See this is where things get very complicated. Just be aware that you get less depth of field with a full-frame camera than you do with a cropped sensor or micro four thirds camera. One for another time. I wish I hadn’t said anything! This has never been a problem for me. Shut up, Rick.
Automatic Modes
Cameras have many different automatic modes. Portrait modes will choose a larger aperture, landscape modes will choose a smaller aperture. In these automatic scene-related modes the camera is choosing what it thinks is the most appropriate aperture for a certain subject matter. The camera matches the shutter speed and ISO to get the best image capture that I can.
In manual and semi-automatic modes you have a say in the aperture that is selected.
Which aperture should you use?
Well, it depends on what you are taking a photo of.
- Use an automatic mode and the camera is choosing that for you.
- If you use aperture priority mode (AV), you choose the aperture and the camera chooses the shutter speed.
- If you are using shutter priority mode, aka Tv, you choose the shutter speed and the camera chooses the aperture.
- If you use manual mode, you decide everything.
What you are taking a photo of?
What depth of field do you need, and how much of the photo needs to be sharp? All of it, or some of it?
What shutter speed is available with that aperture value to give the correct exposure?
Creative stuff
Yes, the aperture gives you creative control of the photos that you take. How the main subject and the rest of the photo relate to each other, and how a photo looks.
Portrait photography – to take a photo of someone, you would use a larger aperture, large enough to blur the background but get all the face in focus.
Take a photo of something fast-moving and you will probably use a larger aperture which lets more light in meaning that you can use a faster shutter speed.
Take a photo of a building and you will choose a smaller aperture to ensure that you get the best quality capture and a greater depth of field, all of the building and surroundings in focus.
Same for landscape photography.
What is the aperture made of?
I don’t know. I have asked Canon, Olympus and Sony and they do not want to tell me. Sounds like a trade secret! I think that the aperture blades are made of metal, they certainly were once, but not so sure now.
Right – talky bit over – what if I use a phone and not a camera?
I am still using an iPhone XS. And with my iPhone XS the aperture is fixed. That is that. So what you do is use something like Portrait mode, where the background is blurred out making the subject more prominent.
Camera phones have replaced the aperture with software. And the price for this? Well, the image quality is not going to be as good as with a camera, but is going to be more than good enough for many uses.
What if I use a film camera?
All the same applies as with digital. And that is all I have to say on this.
What do I do?
What aperture do I use with my photography? I use f/8 most of the time, especially for my photos of buildings. I know that f/8 is the sweet spot on my Canon 17-40mm lens. and I know that with f/8 I get the depth of field that I need using a focal length of 17mm. And I use AV Mode, so I have chosen the aperture and the camera chooses the shutter speed.
Nice and easy!
That is what I do.
Some thoughts from the last episode
Episode 154 was about how to get the correct exposure every time you take a photo – Photography Explained Podcast Episode 154 – How Do I Get The Correct Exposure Every Time I take A Photo?
All I want to do here is repeat the point that we should endeavour to get the best exposure that we can every time we take a photo.
Next episode
Episode 156 – after aperture it has to be shutter speed of course. So that is that. Photography Explained Podcast Episode 156 – What Are Shutter And Shutter Speed In Photography?
If you have a question you would like me to answer just head over to the podcast website – photographyexplainedpodcast.com/start where you can find out what to do. Or just say hi. It would be lovely to hear from you.
That’s all.
This episode was brought to you by, erm, for a change, a cheese and pickle sandwich and a bag of cheese and onion crisps all washed down with a nice cold water, all consumed before I settled down in my homemade, acoustically cushioned, technologically improved recording emporium. Today’s acoustic treatment is one coat and two fleeces.
I’ve been Rick McEvoy, thanks again very much for listening to my small but perfectly formed podcast (it says here), and for giving me 27 ish minutes of your valuable time. I think that this episode will be 24 minutes long after I have edited out the rubbish.
Take care, stay safe
Cheers from me Rick
OK – that was the podcast episode.
Want to know more?
Head over to the Start page on the Photography Explained Podcast website to find out more.
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Thank you
Thanks for listening to my podcast (if you did) and reading this blog post (which I assume you have done as you are reading this).
Cheers from me Rick
