What is Camera Aperture in Photography and What Does it Do?

August 21

21 min. to read

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Camera aperture is one of a photographer's most important creative tools. Find out everything you need to know about it in this article.

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If you haven't figured out perfectly what is aperture in photography, this article is for you. A beginning photographer has a lot of new terms to work into his or her vocabulary. Some of them can be difficult to grasp, especially when they're associated with other, more technical terms like “f-stop”. One of those words is “aperture” and we're about to explore it thoroughly. When you're done reading this post, you should know exactly what it means, why it's important and how to use it effectively. So, what is the aperture of a camera?

An aperture is an opening

Like most photographic terminology, the basic camera aperture definition of this word is simple. If you look it up in the Oxford English Dictionary to explain aperture, you'll find the first definition is “An opening, hole, or gap.” We can even learn from that same page that, to a photographer, it means “A space through which light passes in an optical or photographic instrument, especially the variable opening by which light passes to enter the camera.”

What is an aperture? To help you navigate the setting, all you need to know about the technical construction of the aperture is that it is the opening in the lens that lets light into the sensor. The iris works much like the human eye: when we look at something in the dark, our pupils dilate, but in the light, they contract. The aperture in a lens is almost like its pupil, which can be adjusted manually based on the situation at hand. The values of this parameter can throw a novice photographer into a stupor, because the lower the number, the wider the open aperture. Now we understand a little bit about aperture definition in photography.

Where is it?

This is the next important question after we have dealt with the aperture photography definition. In modern SLR, DSLR and mirrorless cameras, the aperture is located between the elements of the lens. It's created by a mechanism called a diaphragm that controls the size of the lens opening, much like the iris of your eye. That's what you're controlling when you make an aperture adjustment in mirrorless cameras. Most lens diaphragms consist of several overlapping “leaves” that rotate to adjust the size of the opening. As you have already realized, the meaning of aperture in photography is very weighty.

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What does it do?

Coincidentally, the diaphragm also performs the same function as the iris of the human eye – it limits the amount of light that's allowed to pass to the film or sensor in the camera while the shutter is open.  This comparison to the human eye is a very easy way to explain to newcomers what does aperture mean.

The size of the aperture, combined with the length of time the shutter is open, determines the effective amount of light that's allowed to strike the image recording medium. Aperture size and shutter speed are two of the three factors in the “Exposure Triangle”,  a formula that can be used to the exposure of an image. You may decrease or increase the shutter speed for changing the brightness of your photo and creating dramatic effects by either freezing action or blurring motion. Sometimes you will only have to use a faster shutter speed.

There's another important function of the adjustable aperture effect, and we'll cover that in a moment. First, let's make sure you understand aperture size. Once you understand what is aperture on a camera, you need to deal with other important issues.

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F-Stops and F-Numbers

You've probably heard a photographer say something like, “decrease the exposure a stop” or “push it a half-stop.” A “stop” in terms of exposure is the adjustment needed to double or halve the total exposure value (Ev). Modern digital cameras can be adjusted in much smaller increments, but we still use the f-stop as the basis for exposure settings.

Aperture sizes are expressed in f-numbers. Each number represents the reciprocal of its face value multiplied by the focal length of the lens. In other words, an aperture setting of 4 (f/4) on a 50mm lens represents:

¼ x 50 = 12.5mm (the actual size of the aperture)

An aperture setting of f/16  on the same lens represents:

1/16 x 50 = 3.215mm

So, the higher the f-number, the narrower the aperture is and vice-versa.

Calculating actual aperture sizes can get much more complicated, since modern cameras allow you to adjust the aperture in ½ stop or 1/3 stop increments.

Here's a typical full-stop aperture scale:

1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11, 16, 22, 32

Here's a typical 1/3 stop scale:

1.0, 1.1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.5, 2.8, 3.2, 3.5, 4.0, 4.5. 5.0, 5.6, 6.3, 7.1, 8.0, 9.0, 10, 11, 13, 14, 16, 18, 20, 22, 25, 29, 32

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Now we have the aperture settings figured out. Crazy, huh? Fortunately, you don’t have to know the actual aperture size to use this element of exposure effectively. It is important to know the concept, to understand exposure as well as the next term we're going to explore:

Depth of Field

The aperture size also controls the depth of field and sharpness of an image. That's the range of acceptable sharpness in a photo, measured in distances from the focal plane of the camera. The range changes with the aperture photography setting, and shifts with your focus setting. Think of it as an area of sharpness that moves back and forth between your camera and infinity as you focus.

We also talk about wide apertures. Depth of field (DoF) is inversely proportional to aperture size. That means that you can use a wide aperture (f/2.4, for instance) to isolate a sharp subject against a blurred background. On the other side of the scale, you can use narrow apertures like f/16 or f/22 to maximize the sharpness from front to back in a landscape photo (depending on your camera).

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Calculating depth of field is a complex operation based on several factors, starting with the focal length of the lens and the effective aperture size. It also depends on the size of your camera's sensor.

Fortunately, there are a few tools for aperture photography available. You can use an online calculator like this one. You may even have a valuable aid right on your lens. Many lenses have a DoF scale that looks something like this:

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In this photo, the DoF scale is the numbers 4, 8, 11 and 16 located on either side of the focusing mark. Notice how the numbers on this scale align with the distance numbers of the focusing ring (the upper ring). For instance, the 4's are approximately aligned with 3.7ft (0.8m) and 9ft (2.2m). That's where the area of maximum sharpness will begin and end at this focus setting if you select an aperture of f/4. Selecting f/8 will give you a range of about 2.5ft (0.75m) to infinity, and so on.

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In the photo above, the focus has been shifted to slightly over 3ft. Note that f/4 now covers about 2.6ft (0.8m) to about 4.6ft (1.4m) and so on.

There's no substitute for getting the DoF right in an image. Post-processing tools like Luminar Neo can help somewhat, but getting it right in-camera is much more effective.

In the case of modern optics, the drop in sharpness at an open aperture can be almost imperceptible. They all have excellent sharpness at an open aperture but are still sharper when they are closed if you look closely. But old and inexpensive lenses may be outright blurred in such situations. Also, a lot depends on the camera model. The right thing to do is to change such a lens for something more advanced, but if there is no such possibility, try just closing the aperture by several notches.

Large vs Small Camera Aperture

The aperture photography has a major effect on the depth of field. A large aperture (smaller number) will decrease the depth of field, while a small aperture (larger number) will give you a greater depth of field. This can be a little confusing at first. But just remember, a small aperture number means a small depth of field. And larger aperture numbers, mean larger DoF values.

For example, if you take one shot with an aperture of f/22 and the other with f/2.8, you will notice an obvious difference. In a picture with an aperture of f/22, the main subject will be in focus and the background is perfectly distinguishable. In the picture taken at f/2.8, the main subject will be in focus (or part of it), but the depth of field is very shallow and the background is out of focus. Some parts of the main subject may also be less in focus because, at the time of the shooting, they were a little farther away from the camera.

The best way to understand this subject of aperture in photography is to take your camera and experiment. Go outside and find a place where there are objects close to you and move away. Take a series of shots with different settings from the smallest setting to the largest setting with maximum aperture. You will quickly see the difference between pictures taken with a large aperture and a small aperture.

How to Choose Aperture

So, if you open the aperture on the camera wide enough, optical distortion will become noticeable, but if you close the aperture to a certain value, the picture will start to blur due to diffraction. Because of these peculiarities of optics, a legitimate question arises: how to determine the optimal aperture value? 

You need to be very clear about the aperture meaning in the camera. A suitable aperture value will have to be selected for each model of optics. In most cases, the optimal aperture value is about two steps from the maximum value, which is somewhere between f/5.6 and f/11. Lenses differ most in image quality at the maximum open aperture, and vice versa, at f/11 to f/16, the difference between lenses is less noticeable. That's why lenses with the best design and construction are best at fully open apertures.

When choosing the appropriate aperture camera settings, you have to find a certain balance between the risk of distortion or blur and the desired depth of field. It's best to set the aperture in aperture priority mode (Av) or in full manual mode (M). There are some simple practical tips for the photographer. Trying different values of aperture during shooting you need to find the one that gives the best image sharpness. It is advisable to find that value through experimentation and use it in most shooting situations. 

There may be several exceptions. For instance, you might need much light or focus on the main subject - then open the aperture, but be careful not to set the aperture as low as possible (f/1.2 - f/1.8). But if you need a greater depth of field, so that as many objects in the frame as possible are in focus, then you'll have to close the aperture a bit.

For wide-angle optics, it's better to close the aperture down to f/11, while with long lenses you can close it more - down to f/16 - f/22. Keep in mind that you really shouldn't set the aperture too tight, because in that case, you will have to pay for the depth of field with a blurred image due to diffraction.

Aperture for Portraits

When working with a posing model in portrait photography, you can safely play around with the adjustments, thereby selecting the best ones for an aesthetically pleasing shot. To get a beautiful portrait, separate your subject from the background with a shallow depth of field and blurred background. For that, with your kit lens, we open the aperture to the maximum f/3.5. If you have a fast fx lens it is even possible to slightly shut the aperture. For example, if it lets you set it to f/1.4, even f/1.8 might be enough. That way you'll improve detail and get rid of chromatic aberration.

If you want all participants to be in sharpness, ask them to stand at about the same distance from the camera and close the aperture to f/5.6-f/11 so that there is enough depth of field for all faces.

When there is movement in the frame, it's not the aperture settings on the camera that matters, but the shutter speed. Set the aperture to a value that doesn't blur your subjects from their own movements. If you want to strictly control the aperture, you should, first of all, get a sufficient depth of field to place the main characters and insure against small focus errors. In such situations, it's better not to use apertures in the f/1.4-f/1.8 range on fast lenses without the necessary experience.

Aperture for Landscape Photography

In these situations, we start with the depth of field. If you need both foreground and background, select a sufficient DoF so that it covers all the key elements. In that case, we shut the aperture down to f/11 - f/16. If you set it even lower, the sharpness may deteriorate. When there is no foreground, and the subject is far away from you, it is better not to use the widest aperture. Instead, adjust the exposure by lowering the ISO sensitivity. ISO and shutter speed also matters here. A tripod can also help you get better results. 

Aperture in Night photography

When shooting in low light conditions, being able to open the aperture wide can be very useful. For example, if you're photographing actors during a performance in a theater or shooting in a room with low light, you'll need to set the aperture lower. 

For those situations, fast lenses from f/2.8 and below are good. They literally help your camera see in darkness almost better than the human eye. This effect cannot be achieved with budget-priced photographic equipment. For example, Nikon or Canon camera aperture in kit lenses does not go below f/3.5, so it is harder to shoot in darker conditions than light fixes.

That's it for the basics!

So, try photographing the same scene with different apertures. Determine the optimum value for your lens that gives you the sharpest, highest-quality picture. If you want to blur the background more or to make all the objects in the frame sharper, just make sure you increase or decrease the shutter speed value by a couple of notches from the optimal value.

There are other things associated with aperture, such as diffraction, bokeh and hyperfocal distance, but those are separate lessons. By now you should have a good working knowledge of the aperture and how it affects your photos. Go practice!

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