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Understanding camera aperture and why it matters

For the past three years or so, every time a phone is announced and they get to the part about its camera, the word "aperture" gets thrown around. With the Galaxy S9 unveiling right around the corner, you're about to hear it again. And if rumors about a camera lens with an aperture you can adjust are true, we'll be hearing at least 200% of the recommended dose of aperture talk. But what does it mean? What is it exactly?

In its simplest form, an aperture is a hole that light travels through. When talking about photography, the "hole" is the opening in front of a lens (not the lens diameter itself), and the word aperture takes a bigger meaning and becomes a setting that the photographer can reference. It's one of the three basic pillars of image capture, along with ISO and shutter speed, and while the science and math involved make the aperture setting important for a long list of reasons, the two most important to anyone taking a picture are the focal point and exposure. Ready to dig into all of that until it makes sense? Great! We are, too.

Photography's love triangle

Earlier I mentioned that aperture is one of the three pillars of photography along with ISO and shutter speed. Together, the three settings are known as the exposure triangle and each can have a dramatic effect on how good a photograph looks. They affect more than the exposure (brightness) of a picture, so don't let the name fool you — together they are the biggest factor in making a picture look great or horrible.

Any change to aperture, shutter, or ISO affects all three settings.

The three settings need to be balanced, so you really can't talk about one without explaining a bit of what the others can do. A camera needs to be able to freeze a moment in time and recreate the right colors in the right places and be able to define the right edges, and aperture, ISO, and shutter speed are the three settings that make it happen. You simply can't adjust one setting without adjusting at least one of the others if you expect to take a great photograph.

ISO

ISO is a measurement of the sensitivity of your camera's sensor to light. Way back when actual film was used, you bought different ISO-rated film because there were no sensors and ISO was a non-adjustable part of an image's exposure. We have things a good bit better now. With a modern digital camera, we can control the sensitivity of the sensor on the fly. Technically, we're controlling the level of post-capture gain applied to the signal because that's easier, will greatly lengthen the life of the sensor, and provides identical results.

A lower ISO means less noise.

Ideally, a lower ISO is better because that means there is less noise (pixels that aren't a recreation of the real-life setting) in the final result for any post-processing to filter out. When processing has to remove noise it does so based on the pixels around it that aren't noisy and makes an educated guess. Less guessing means a better photo. But it's not practical to use a super-low ISO setting most of the time because the shutter speed and/or aperture opening can't compensate.

Increasing the ISO setting raises the sensitivity to light, which allows you to take a photo using less light from any source. There are three things to remember about the ISO setting:

  • The lower the ISO number the less sensitive the sensor is to light. The higher the ISO number the more sensitive the sensor is to light.
  • The signal picks up more noise as it becomes more sensitive. That means lower ISO numbers have less noise and higher ISO numbers have more noise.
  • When you can't open the aperture wider or can't slow down the shutter, you use a higher ISO to "freeze" motion and take a picture that's not blurry.

Shutter speed

Shutter speed is the measurement of how long the shutter stays open when you take a photo or capture a frame of a video. When the shutter is open light is coming in, so faster shutter speeds can't collect as much and the exposure is lowered. Of course, the opposite is true and a slower speed results in a higher exposure. Think of exposure when used this way as the brightness or darkness of the photo after everything is done and you'll have a handle on what it means.

Lower is faster when talking shutter speeds.

While the shutter is open the sensor is collecting data about everything it can "see." When any part of what's framed in front of the sensor is moving, the result will be blurry, so most of the time a faster shutter speed is better for getting a sharp and in-focus photo.

  • If you decrease the shutter speed (also known as a faster shutter), you need to raise the ISO or open the aperture to increase the exposure. But your photo will be sharper with a faster shutter.
  • If you increase the shutter speed (a slower shutter), you might need to lower the ISO or close the aperture to decrease the exposure. But your photo will be less sharp and maybe even blurry with a slower shutter.

Every camera has a shutter, even your phone. Film cameras need an actual mechanical curtain to open and close, but many digital small-sensor cameras (including your phone) just time the capture of data as the shutter. This is why you can turn the shutter sound on or off on many phones; nothing is really moving to make the noise, it's just generated by the software and timed to the shutter release.

Aperture

Aperture is the measurement of how open (or closed) the iris of a camera lens is. It's measured in f-stops, which are an expression of the ratio of the focal length (distance from the focusing point on the lens to the front of the sensor) to the diameter of the iris (the hole in front of the lens). You don't need to remember that or do any math, but you do need to know that a lower f-stop number is a wider aperture and that allows more light to go through the lens and reach the sensor.

  • A more narrow aperture (higher f-stop number) needs a slower shutter or a higher ISO setting to increase the exposure.
  • A wider aperture (lower f-stop number) needs a faster shutter or a lower ISO setting to decrease the exposure.

As you can see, the aperture is only one part of what makes a properly exposed photo. But like shutter speed and ISO, aperture also has an effect on sharpness. Each part of the exposure triangle also changes another element of your photo when they are adjusted. Changing ISO can increase noise, changing shutter speed can increase motion blur, and changing aperture changes what's called depth of field.

Everything is not portrait mode

You might be wondering why the aperture on your camera isn't just super-low to let in all the light it can. Well, besides making the photos overexposed in many cases, the depth of field would be too narrow.

The right depth of field can make a good picture great.

A depth of field is the distance between the closest thing in a photo that's in focus and furthest thing in a photo that is still in focus. A camera lens can only bring things into focus at one spot. Anything outside of that exact point is not in focus and blurred outwards from the center point in the shape of the aperture. The parts that appear to be in focus to our eyes are in the depth of field.

When something is far enough away, the difference between a f/5 aperture (left) and a f/25 aperture (right) is minimal as long as the equipment can adjust the ISO and shutter speed enough to compensate. Your phone can't and the result would be noisy. Very noisy.

Ignoring aperture, ISO, shutter, and exposure the biggest diameter depth of field a lens is capable of creating is called its circle of confusion. The diameter of the depth of field increases the further the lens is from the point it is focused on until you reach the circle of confusion. That means taking a picture of something across the street has a wider depth of field that taking a picture of something a few inches away with the exact same settings. To our eyes, a lens focused on something far enough away will appear to have a full-width depth of field where everything we can see is in focus, but camera sensors can process what is in front of it far better than our eyes can.

What we see versus what we get

What matters most s what we can see, not what the lens can capture.

The depth of field is what determines which areas in a photo are in focus. Normally, we want a picture that is clear and sharp throughout, but with an obvious point that draws our eyes. The photographer needs to make sure the subject is framed in a way that draws the eye to it, but the depth of field is what makes that spot more "crisp" than the rest of the photo. Ideally, everything is in focus and we can't see where the actual point of focus drops off and instead we just perceive a slight difference. Photography is part optical illusion along with part art and part everything else.

In short, the people working for a company who makes camera lenses have a lot to consider and a lot of very complex math to sort out. When they are designing a very tiny fixed lens in a smartphone, it all gets even more complicated. And it's very important because, above all, we want our pictures to look great no matter what numbers are thrown at us.

Awesome portraits

Portrait photography is an exception to the general rule. When you have a single subject — that could be one person or a pet or a group of friends or anything else — that you want to stand out against a simple but pleasant background, a portrait photo can look incredible if done correctly.

Normally, a portrait uses a wide aperture to create a narrow depth of field. Along with proper exposure and slightly tweaked color, this creates a result where the subject looks isolated from the background. This is easy for a camera with a bigger faster lens and full manual controls, but not so easy for something like a smartphone.

The Pixel 2 uses a pure software solution to take normal photos (left) and Portrait Mode photos (right) at the same time.

Different companies are trying to do portraits in different ways. Google and Huawei are using machine-learning along with capable hardware to create portraits through software and processing. Samsung is focusing (pardon the pun) on hardware first to give multiple angles and focal lengths to the image processor. Apple is doing both. Neither is new, we've seen multiple lenses and software-adjustable depth of field from companies like Nokia, ZTE, LG and more for the past five years, but technology has moved forward and the results are a lot better.

Notice I said "better" and not perfec. While it's possible to get a great portrait photo from any of the capable flagship phones, most photos are average at best. They all seem to miss the subtlety at the edges of the depth of field and apply a uniform blur to the background, making things look a bit unnatural. Creating a depth of field effect that looks good every time is tough, but we're getting there.

An adjustable aperture on a smartphone?

If the rumors are true, we'll see a camera that has a user adjustable aperture on the Galaxy S9. Details are sparse so we don't know if this means an actual mechanical way to open or close the iris on the lens cover or software that can control the depth of field effect.

I'm betting this means a way to adjust the focal point like we've seen from plenty of companies and a way to adjust the actual depth of field effect versus just blurring some parts of the photo after processing. Smartphone veterans will remember that Nokia's Refocus feature did something very similar to what I'm describing. Modern hardware should be able to acquire all the data needed much faster than we saw in 2013 and taking photos won't take as long or be as fiddly.

No matter how Samsung delivers an adjustable aperture, if they do it's easy to understand why. It all goes back to the depth of field.

2017's hardware should be a lot better at adjusting a depth of field that 2013's was. And 2013's hardware wasn't bad at all.

Most small lenses designed for the types of image sensors our phone use are shaped and ground so that they are sharpest with a depth of field somewhere between ƒ/5.6 and ƒ/8. This is very narrow and doesn't allow for a lot of light, but it cuts back on chromatic aberration making the colors your camera reproduces as close to the original as possible. Using a fixed aperture system set at even f/5.6 is not going to produce photos that are well-exposed without a high ISO (remember, this means a lot of noise) and/or a slow shutter (which means blurry photos) so the aperture is widened and a bit of sharpness is exchanged for a much more flexible system.

As cameras in our phones inch closer to ƒ/0.5 (the theoretical maximum according to Sidney F. Ray's Applied Photographic Optics (opens in new tab)) more and more sharpness in normal photographs is sacrificed. It's difficult to slow the shutter enough to allow for proper exposure and produce photos that are properly focused and sharp, so ISO is increased and the SNR (signal-to-noise ratio) gets higher and higher. And this does nothing to address the narrow depth of field when taking normal or wide-angle photos.

We've seen pixel sizes grow to compensate and camera circuitry is built to deal with noise a lot better than it used to be, but if you're a company who wants to focus on using hardware for better photos and not software, the next logical step is to perfect a way to use multiple apertures. I'm not sure exactly what to expect from Samsung with the Galaxy S9's camera, but Samsung needs to take the next step and is more than capable of doing it.

Take better pictures

Now you know a little bit about what aperture is and how ti affects the pictures you take. So get out there and take some!

And remember the next time someone on a stage tells you that this awesome new phone has an amazing f/something aperture, there's more to a great camera. A lot more.

Jerry Hildenbrand
Jerry Hildenbrand

Jerry is an amateur woodworker and struggling shade tree mechanic. There's nothing he can't take apart, but many things he can't reassemble. You'll find him writing and speaking his loud opinion on Android Central and occasionally on Twitter.

33 Comments
  • Next up: Sensor size Please...
  • I want one more phone with Nokia 808 Pureview or Lumia 1020 sized sensor.
  • Enjoying my lgv30. Took some pretty good shots of the full moon last night. Would gladly share, but I do not know how to include a picture here. Lol. I'm. Guessing a link to a Google drive or something
  • From your Google Photo album, click on the picture, click the "share" icon, click on "get link", click "copy", then you can paste it here in the forums like below. Note: These are reduced quality, but untouched otherwise. Sun setting behind Tim Horton's
    https://photos.app.goo.gl/LNYOxIuneHpMINPW2 Winter bloom
    https://photos.app.goo.gl/7witUxGJaMsKdsWo2 Field trip
    https://photos.app.goo.gl/VnSkNmh3YUmFL8uB3 The drive home
    https://photos.app.goo.gl/t4hVLmHCQ7jaAN282
  • Thanks for this article, Jerry. This is very helpful in the explanation of very technical terms in a way someone new to photography would be able to understand.
  • I've had nothing but Galaxy phones for years, and am currently using a Galaxy S7 Edge, but I don't understand how variable aperture is a new thing to people or how Samsung is trying to create some artificial newness out of it. Huawei has had this for YEARS, back to the Honor 6 plus 3 years ago! And even had a slider for the aperture that went from f/0.95 all the way to f/16. They even support variable aperture on their basic phones like the Honor 7x. The Nokia N86 also had 2 different apertures that you could choose from and that was back in 2009! Samsung is going to need to do wayyyy more than aperture tricks to make me think the S9 is worth buying.
  • Is it actually physically changing the aperture, or it is simply mimicking aperture in software?
  • This is all digital, they would not have a mechanical variable aperture...that's only been done that once with the super expensive folder phone the W2018, and even that is not a variable aperture, it's 2 set values. There's an iris that goes from one aperture size to another (1.5 to 2.4) but the S9 would have a single camera so would use purely synthetic aperture changes, using the dual pixels just like the Pixel 2 XL. On the Huawei, the interface gives you a default value and there's a slider that lets you change the aperture. Not sure what the S9 will do, but regardless, none of this is new. I think Samsung is just trying to use their marketing genius into making people think it's new.
  • New or not, software mimicking physical aperture changes simply won't work as well as a real aperture that changes. I don't know how the S9 is going to handle it, and don't really care, since I don't buy a phone for its camera.
  • That's different. Huawei uses it as an equivalent to help adjust the amount of software blur. F-stop values need to be weighed with the actual focal length of the lens. We don't know how Samsung will do it but if it's physical, it can actually be used to help with sharpness in daylight shots.
  • Part of me wants to see an actual way to change the iris. this is Samsung, who can pull it off and make people interested in it. What I think we'll see is something that lets you take a photo then change the focal point and set an aperture value in the final image processing. A lot of these rules about exposure and DoF can be changed when everything is digital if the right person thinks up the right way to calculate it. When it comes to phone hardware and features, Samsung goes all out in ways no other company does (or can). If someone at Samsung thinks they can expose an image in a way that doesn't factor in a physical aperture size, money will be spent and people will have the freedom to try new things. That's what I love about Samsung.
  • Like you said, Samsung did it physically on the W2018 and that’s EXACTLY what they’ll be doing on the S9. it’s not a cheap software trick like Huawei’s, and even if it’s not the first time we’ve seen it (the Nokia), it’s the only current phone that can. Since it’s not just mimicking the effects with software and actually using a physical blade like the W2018, this is going to be a huge selling point for Samsung because, again, they’re probably going to be the only manufacturer this year capable of doing it. Why are you so convinced that it’s going to be all “synthetic” or “software-based” when Samsung already did it with A FLIP PHONE?
  • it’s physically changing it, look at the W2018 - there’s a gif showing the actual camera lens changing when the aperture is switched
  • Way to comment twice and rant about something you're completely wrong about.
  • This is all digital, they would not have a mechanical variable aperture...that's only been done that once with the super expensive folder phone the W2018, and even that is not a variable aperture, it's 2 set values. There's an iris that goes from one aperture size to another (1.5 to 2.4) but the S9 would have a single camera so would use purely synthetic aperture changes, using the dual pixels just like the Pixel 2 XL. On the Huawei, the interface gives you a default value and there's a slider that lets you change the aperture. Not sure what the S9 will do, but regardless, none of this is new. I think Samsung is just trying to use their marketing genius into making people think it's new.
  • That's still variable compared to everything else on the market and what makes you believe they can't do it on the S9 if they've actually done it with the flip phone?
  • All I'm saying is that none of this is new and/or should be considered as such. They need to do more than aperture to make this a worthwhile upgrade.
  • That's for customers to decide. Like I said, it doesn't matter to me, but it might be enough to attract someone.
  • "That's for customers to decide" +1 If the photos look noticeably better, then this is definitely a selling point for me.
  • The s9 more likely to have the same mechanical aperture as the flip phone. Probably on the cheaper one. This way both the regular and the plus can switch. The plus doesn't need it because it has 2 cameras on the back . each one with a different aperture. There was a leak of the s9 box that kinda proved my theory.
  • Dude, you're dead wrong.
  • Aperture is very misleading without specifying the sensor size. That is why reviews of serious cameras always list the sensor size before they talking about any other camera specification (eg full-frame, 4/3, APS-C sensor sizes). The cell phone companies have apparently fooled the bloggers into thinking sensor size is irrelevant.
  • You also need to mention the focal length in relation to the sensor size. Note that smaller sensors will tend to have a crop factor, which gets bigger and bigger the smaller the sensor gets. To achieve the equivalent focal length FoV on a 35mm full-frame camera, the focal length would have to be smaller depending on the side of the sensor to achieve the desired FoV. For instance, your phone with a 1/2.6” sensor may have an equivalent focal length of 26/27mm on a 35mm full-frame sensor but its actual focal length is somewhere around 4.3mm. Hence, an f-stop of f/1.7 is actually smaller than the same f-stop on a larger sensor camera.
  • It should be more about pixel size in the sensor not the size of the sensor itself. Arent the sensors in samsungs s7 and above bigger then most smart phone sensors? They are bigger because they have more pixels . half of the pixels dedicated for focusing.
  • I Never owned a point and shoot camera past my Blackberry 9650. I didnt need one, I had a camera phone. The best camera I had was the one I had on me. As "camera phones" progressed, I progressed. I upgraded to the galaxy s2 then to the LG OG. Now owning through the LG series to the G6, I was wanting more out of the camera phone that I have always kept with me. I learned a little how to tweak images in manual mode but it only took me so far. I always wanted an interchangeable lens camera but the size and "all of those settings" scared me. I very recently ran across a Sony a5000 for a steal of a price, and took the plunge. I still have a lot to learn but this article helped explain some of the details I was looking for and in a way I could understand. Thanks Jerry for all the photography wisdom you impart so newbies like myself can grow in this amazing hobby
  • Technical article: Yay!
    From Jerry: Double Yay! Thanks Jerry, this was good. I wasted a lot of film playing with shutter speed and aperture when I was a kid, but it was fun. You had to choose ISO carefully back then because it could not be changed once you loaded the camera, lol. I remember the fun in moving from a full wet darkroom to a vintage Polaroid 95A, and that crushing day when the local supply store stopped carrying the film. C'est la vie... I also cast my vote for an article on sensor size!
  • Interestingly, no mention of HTC who had portrait mode before Apple and post capture adjustability before Samsung. I hang onto my old M8 for two reasons other than it's a nice phone: It still has THE best audio quality of any smartphone, bar none, and the portrait mode and 3D photos are still fun.
  • well HTC’s cameras were so bad back then that even with bokeh, they couldn’t sell it. apple was among the first companies to introduce some sort of bokeh effect while still having good camera quality
  • I appreciate the variety of topics the staff at Android Central cover on a daily basis, but I particularly pay attention to Jerry articles. Extremely helpful in understanding important aspects of photography.
  • Due to the sensor size this is more marketing than anything else.
  • Great topic as usual Jerry, thank you. I enjoyed every word of it and now I know better. Sometimes we get carried away and tricked by all the marketing, it’s always more important to understand what is really being sold to you. With that you can then appreciate what has been achieved or scoff at it what you are being told has been achieved, with the correct information you know which one to do than being just a fanboy.
  • Understanding these principles is key to taking the picture you want to take. The most important element remains the eyeball behind the viewfinder and the brain behind the eyeball. Composition is a learned skill and the technology is merely a tool to effect the composition desired. I stood in the same place Ansel Adams did to take his iconic picture of the Grand Tetons and the Snake River, but could never match the incredible skill in his eyeball and brain. I still prefer my Nikon D7100 over my phone, but the phone can be awfully handy. Thanks Jerry for a good article.
  • Don't forget it's also the post-processing photo editing skill... even with Adams.