In the photo below, the person in focus is wonderfully isolated from the blurry background. This is an effect we refer to as bokeh, made possible by a small aperture. Because of the bokeh, our eyes are less distracted and drawn to the subject. We consider this effect beautiful because it comes very close to our own cognitive experiences. In fact, we can recreate it without a camera. Just focus with your eye on a nearby object and you will notice how everything in the background starts to blur.
In this guide, we explain–in simple terms and examples–aperture and how to creatively control it.
What is Aperture?
Aperture is a hole inside your lens through which light enters your image sensor. The size of the hole—which determines the amount of light passing through—is regulated by a series of aperture blades. Opening and closing the aperture blades can give you a wide or narrow aperture. A wide aperture lets more light into the image sensor. A narrow aperture lets less light into the image sensor.
Measuring Aperture: F-stop
f-stop is a measure of how wide or narrow the aperture is. It can be confusing to beginner photographers because the f-stop is inversely proportional to the aperture. For example, a smaller f-number such as f/1.8 indicates a large aperture (wider opening) which means more light will pass through the lens. And on the opposite, a large f-stop such as f/11 indicates a smaller aperture (narrow opening) and less light will arrive at the image sensor.
Aperture and Depth of Field
Controlling Depth of field (DoF) is one of the most useful creative tools in photography. The depth of field refers to the depth of the in-focus area in front and behind your focus point. A shallower depth of field allows you to isolate your subject and blur the rest. A deeper depth of field keeps everything from foreground to background elements in focus. While the depth of field depends on other factors (such as lens focal length and focus distance), aperture plays a major role.
A larger aperture gives you a smaller depth of field. For example, in the bird photo below, we use a larger aperture (such as f/2) to get a smaller depth of field. Doing so has isolated the focus on the bird while blurring the background to give us a wonderful bokeh effect.
There are times when you want to do the opposite and get more depth of field. For example, in the landscape photo below, we want to get both foreground wildflowers and the background mountains in focus. To do so, you need to use a smaller aperture (such as f/11) to get a larger depth of field. Here’s an example.
Illustrating Aperture’s Effect on Depth of Field
To further explain how the aperture affects your depth of field, I photographed this row of Matryoshkas while aiming the focus point on third last Matryoshka, I call her Babushka.
In the photo below, at aperture f22, we have a large depth of field that covers all 7 Matryoshkas.
For the next photo, I used a larger aperture at f/11 which gives us a shallower depth of field compared to f/22. As a result, details of the couch are starting to blur heavily compared to f/22. You will also notice that the first two Matryoshkas can’t hold up with the other six in terms of focus.
At f/1.8, the aperture is completely open and the depth of field has gotten very small. The only one holding up is Babushka. She is sharp and beautiful as ever. Objects that are in front and beyond her are melted in a sea of blur!
In conclusion, depth-of-field describes the distance between the nearest and farthest objects in a scene which appears acceptably sharp in an image. Everything inside the depth-of-field appears sharp, everything outside starts to blur! The smaller the f-number, the shallower the depth-of-field. As we mentioned earlier, the creamy areas outside the focus are referred to as bokeh. The figure below illustrates this further.
The figure below illustrates this further.
Aperture and Exposure
As we mentioned earlier, aperture refers to the size of the hole through which light passes through your lens. Following series of F-stop numbers are known as the F-stop scale. It is important because jumping up one full stop (for example from f/1.4 to f/2) means that half the light will pass through your lens. Jumping down one full stop (such as going from f8 to f5.6) means that double the light will pass through your lens!
Unlike ISO and shutter speed scales which are easy to learn using simple math, the F-stop scale is slightly more complicated to predict. Since these numbers are irregular, most people find it easiest to just memorize the sequence.
Let’s make a brief example. You want to shoot a portrait with ISO 400, aperture of f/4, and a shutter speed of 1/500. After you take the picture you decide you’d like a little more bokeh so you open up the aperture to f/2.8. According to the above f-stop scale, doing so would double the amount of light available to the image sensor. As a result, you need to increase your shutter speed one full stop (for example, from 1/500 sec. to 1/1000 sec.) in order to keep the same exposure.
Lens Speed and Aperture
If you look at the specifications of your lens, it will indicate the largest aperture (lowest f-stop number) it supports. This number is important because it indicates how much your lens can be opened up to let light in. The smaller the f-stop your lens can achieve, the bigger the amount of light it can pass through to your sensor.
Lenses with wide apertures (such as f1.8) are often referred to as fast lenses. This is because at wide apertures there is more light passing through the lens, allowing it faster shutter speeds. You might then wonder why all lenses don’t have wide apertures. This is due to the material cost of manufacturing large glass elements to afford a larger aperture. Prime lenses usually have wider apertures than zoom lenses and can be relatively cheaper as well. Learn more about how a prime lens can improve your photography.
Controlling Aperture Creatively
So far we explained how aperture controls the amount of light that passes through to the image sensor. We also covered how aperture affects the depth of field. But what does all this means to your photography? More importantly, how can you use this knowledge in your pursuit of taking better photos? Here are few ways you can use your knowledge of aperture creatively.
When you are photographing a sporting event or a kids’ birthday party, you might want to freeze action in your shots. To do this, you need a faster shutter speed. One way to get a faster shutter speed is to open up your aperture as much as possible (for example f/2). By opening the aperture wide open, we let more light into the image sensor. As a result, we are able to achieve the desired exposure faster and freeze action.
Create Motion Blur
If you want to capture motion blur, you would need a slow shutter speed. You can do this by lowering your aperture (large f-stop like f/11) to limit the amount of light that is reaching the image sensor. Since there is less light available to the sensor, it will need to keep the shutter open for a longer time (slow shutter speed). This can be a very useful creative tool when you want to give your viewers a sense of motion. For example, you might want to capture motion blur when capturing waterfalls, people, transportation, light trails…etc.
Shooting in Low Light
Opening up your aperture can let enough light in when you are shooting in low light conditions. For example, if you are shooting a party at night, you can still get a decent picture without using a flash if you have a faster lens. Remember, a faster lens means a lens that can have a large aperture (smaller f-stop such as f/1.8). Experiment in low light conditions using your lens to see how it performs at the widest aperture in low light situations.
Isolate Your Subject
As I mentioned earlier, using a larger aperture creates a shallow depth of field. Which results in blurring of areas that is not within the depth of field. You can use this effect to isolate your subject from background and foreground distractions. Doing so really helps to guide viewers to your subject. Learn more about isolating your subject to get better photos.
The takeaway of this fundamentals guide should primarily be that aperture values tell you how much light is passing through your lens and they determine depth-of-field. You can use aperture in order to get your exposure right and you can use it to isolate your subject from the background.
Do you have anything to add to this knowledge? Have you found it useful? Please leave a comment below and we would love to hear what you have to say.
Download FREE Photography Lighting Cheat Sheet
Subscribe and get a free downloadable photography lighting cheat sheet