Usually, when people think about factors that contribute to great quality smartphone photos they think about the megapixels or sensor, and overlook one of smartphone photography’s unsung heroes– aperture.
But, what exactly is aperture?
Aperture is the opening in the camera lens through which light enters the camera. How dark or bright the photo that the camera produces will turn out is determined by the size of this opening, the size of which is expressed in f-stops.
The smaller the f-stop number, the wider the opening and, ultimately, the more light reaches the sensor. Aperture can be adjusted on traditional cameras but smartphone cameras commonly have a fixed aperture.
How does aperture work?
In order to fully understand how aperture works on smartphone cameras, you need to understand how it works on dedicated camera lenses. You also need to understand how it affects the image that is captured.
How aperture works on dedicated cameras
On digital cameras with bigger lenses, aperture works pretty much in the same way as the iris in our eyes, which expands and contracts to regulate how much light hits the photoreceptors in our eyes.
Similarly, a digital camera lens has a mechanical diaphragm that controls how much light enters the camera and hits the sensor. On the barrel of a typical DSLR camera lens, there’s a ring that you can turn to adjust the size of the aperture.
Altering the aperture allows you to creatively manipulate things like depth-of-field. For example, shooting with a wide aperture will give you a shallow depth of field, which is perfect for portraits.
If you’re shooting things like landscapes, the best thing to have is a deep depth-of-field, so that everything in the foreground and background can be in focus. This can be achieved by narrowing the aperture.
Illustration of how aperture affects images.
What does the “f” in f-stop mean?
Aperture is expressed in f-numbers also referred to as f-stops. These are alphanumeric figures (f/1.8, f/2.2, f/8, etc.) found on the lens that match specific aperture sizes. Each f-number is a fraction that tells you how big the diameter of the aperture is at any given f-stop.
The ‘F’ stands for focal ratio and is calculated as
where ‘f’ is the focal length of the lens, and ‘D’ is the diameter of the aperture.
Focal ratio= focal length of lens/diameter of the aperture
To calculate the f-stop numbers for a particular lens, the lens’s focal length in millimetres is divided by the size of the aperture in mm.
Aperture and depth-of-field
Aperture not only affects the brightness of an image, but it affects the depth-of-field as well. Depth-of-field refers to how much of the picture is in focus from the foreground to the background.
A deep depth-of-field means whatever is in the foreground and anything in the background will be in focus when you take a photo.
A shallow depth-of-field, on the other hand, has a more limited area of focus. This means that you can have a sharply focused subject in the foreground with a blurry background.
Simply put, the wider the aperture, the shallower the deep-of-field. The narrower the aperture, the deeper the depth-of-field.
Therefore, if you’re shooting portraits on a camera such as a DSLR, you’d use a low f-stop (wide aperture) like f/2.0 so that you have your subject in focus and the background nicely blurred.
For landscapes and wide shots, you’d use a high f-stop (narrow aperture) so that more of the detail in the background and foreground is in focus.
To make sure you don’t under- or overexpose when adjusting the aperture, you need to be familiar with the exposure triangle. You can learn about it here.
How does aperture work on smartphone cameras?
Unlike with traditional cameras, the vast majority of smartphone cameras have a fixed aperture. This means that if a smartphone is said to have an f/2.2 aperture, then that is that. You cannot change that to allow more light or less light in by adjusting the aperture.
This may sound limiting (and it is) but due to size, smartphone cameras need their aperture to be as wide open as possible in order to allow enough light to reach the tiny sensor.
But smartphones have wide apertures, why don’t they have shallow depth-of-field? It all boils down to size. Again.
Smartphone camera lenses have shorter focal lengths than any other type of camera lens. This is mainly because of the size limitations and design of the smartphone camera unit.
And with a short focal length, you get a much broader angle-of-view, and thus a wide-angle shot. Wide-angle shots don’t usually have blurry backgrounds.
So, despite having a wide aperture, smartphone cameras will mostly produce photos with a deep depth-of-field. However, thanks to computational photography, smartphone cameras can simulate the bokeh effect (blurry background) pretty well these days.
To understand focal length and field-of-view better, I recommend you read this article.
There are some phones that have implemented variable aperture in their cameras. Back in 2009, Nokia introduced the Nokia N86 8MP, which had many firsts including a variable aperture with three f-stops.
Variable aperture wasn’t seen again in a smartphone camera until nearly a decade later when Samsung added dual aperture to their devices, starting with the Galaxy S9 in 2018.
Samsung Galaxy S9 with variable aperture
Very few smartphone cameras have variable aperture because this is a somewhat new-ish technology, which sounds really good in theory.
The benefit of this is that if you’re taking photos in a dark environment, the camera will switch to a wide aperture in order to let in as much light as possible. This is great for night photography because your photos will come out brighter and less noisy.
On the other hand, if you’re shooting in daylight, the camera will use the narrower aperture to limit the amount of light coming in. This will improve the photo’s sharpness around the edges (where the lens is weaker) and prevent overexposing the shot.
As exciting as a variable aperture on smartphones sounds, it’s currently very limited. On the Samsung Galaxy S10, you can only select between f/1.5 and f/2.4 on only one of the three rear cameras.
Samsung excluded this feature in their Galaxy S20 series.
No matter the improvements in technology, smartphone cameras will never compare with DSLRs. An aperture as large as f/1.5 on a smartphone might be impressive but it won’t give you the same results as you would get on a larger camera.
In fact, f/1.5 on a smartphone camera could be equivalent to a much narrower aperture on a typical camera lens.
The aperture may be the last thing on your mind when considering what to look for in a good smartphone camera but it plays an important part, especially in low-light conditions.
Even though currently most smartphones only have a fixed aperture, it’s still good to know your phone’s aperture and how that limitation impacts your photography. That way, you can learn to get the most out of your smartphone camera despite its limitations and take amazing photos with it.
If you are new to mobile photography and would like to improve the quality of your smartphone photos, I recommend you download this free 22-page ebook that will teach you how you can do exactly that. It is simple and easy to understand, yet very informative. Best of all, it’s absolutely free! Download your free copy here.