What is Aperture in Photography? A Complete Guide

Understanding aperture in photography is understanding one of the fundamentals of how your camera works. It’s one of the three important points of the exposure triangle (along with shutter speed and ISO). By understanding aperture, you’ll be well on your way to shooting perfect exposures and having maximum creative control over your images.

The aperture is the hole in your lens that opens and closes to let light into the camera. It has a significant effect on both exposure and depth of field (DOF) in the image. However, it can be a little confusing at first and can often seem counterintuitive, particularly for new photographers.

What is aperture, and why is it important?

In basic terms, the aperture is the opening in the lens that lets in light. It works very similarly to the pupil of the eye – it can become bigger when it needs to let more light in and smaller when it needs to let less light in. By adjusting the amount of light hitting the camera sensor, you can control the exposure of your image.

The aperture also affects how much of the image is in focus front to back (depth of field), although without wanting to overcomplicate things, depth of field is also dependent on other factors. Some people might argue that this is the most important aspect of understanding aperture, and in a creative sense, it probably is. Having the ability to decide which aspects of your image are in focus is an important part of creating an intentional and engaging composition.

Aperture and F-stops

Aperture values are measured in stops, or F-stops, as they are known. It’s an abbreviation of focal ratio. To calculate, you just divide the focal length of the lens by the diameter of the aperture opening.

You might have noticed that on your lens, you have a series of numbers. Those numbers refer to the F-stops so that you know how large your aperture is when taking a photograph.

Now for the part that often seems confusing at first. The higher the F-stop number, the smaller the aperture. Conversely, the lower the F-stop, the wider the aperture. So, for example, an aperture of f/16 will let in a small amount of light through to your sensor. An aperture of f/1.8 is a wide aperture and will let through a lot of light to the sensor.

Light is also measured in stops, the same as the F-stops on your lens. The scale below is full stops of light:

You might notice some additional numbers, say f/1.8, for example. Many lens manufacturers will let you choose third stops, or half stops as options as well for even greater accuracy.

Fast and slow

The F-number of the lens corresponds to the widest aperture that the lens will open up to. So a 50mm f/1.4 lens has a maximum aperture of f/1.4, which is pretty wide. These lenses are referred to as ‘fast lenses’ because they let in a lot of light. A 24-105mm f/4 lens will only stop down to f/4, which obviously lets in considerably less light than the f/1.4 lens will.

You will find that some manufacturers make two versions of the same focal length of a lens: a fast version, and a slower version. The fast version will usually have a much wider aperture value and will be noticeably more expensive.

How does the aperture affect exposure?

As you can see, aperture is very important when you want to control how much light is entering the camera. It has a considerable effect on the overall exposure of the image. Alongside shutter speed and ISO, it makes up the three pillars of exposure, as seen in the exposure triangle.

So how does this work? It’s actually fairly simple. When you adjust one of the three values (shutter speed, aperture, or ISO), you vary the overall exposure of the image.

If you increase your f stop by one whole stop of light, you actually halve the amount of light getting into your camera. For example, if you increase your aperture value from f/11 to f/16, you are effectively letting in half the amount of light. Conversely, if you change your aperture from f/8 to f/4, you are increasing the amount of light by 2 whole stops, which essentially amounts to 4 times the amount of light let into your camera.

How aperture affects depth of field

Now, we said earlier that the aperture does two things: exposure and depth of field. Depth of field, in basic terms, is the amount of image that is in acceptable focus, from the foreground to the background. Being able to choose what is in focus can have a considerable effect on your creative process.

So how exactly does the aperture affect the depth of field? Generally, a wider aperture will give you much less depth of field. That means that less of the image will be in focus from front to back. For example, at f/1.4, very little of the image will be in focus. In a portrait, just the eyelashes could be in focus, for example.

Alternatively, if you wanted the entire image to be in focus as much as possible, you would want to shoot at f/11 or f/16, depending on which lens you were using.

Depth of field also depends on the focal length and how close your subject is to your lens. Generally, a wider angle lens will give you a greater depth of field than a telephoto lens. Shooting close to your subject will give a shallower depth of field than a subject further away. I know there are so many variables, but with practice, it gets more intuitive!

Examples

How does the aperture affect diffraction?

Diffraction happens when light bends to move around an object in its path. In the camera’s case, the object blocking the path is the lens. The amount of diffraction going on depends on the aperture that you’re shooting at. It can cause minor distortions that present as the image or parts of the image having a slightly softer focus.

Diffraction doesn’t really become obvious unless you’re shooting at the extreme apertures of either end of your lens, say at the widest or narrowest. The smaller the aperture, the more the light has to diffract through the opening of the lens to hit the sensor or film.

That means that if you’re shooting at f/22, the image actually won’t be as sharp as it could be at f/8. Generally speaking, shooting in the mid-range of your lens’ aperture range will yield the sharpest images.

How many aperture blades do you need?

To answer this, we need to look at the insides of a lens. The lens controls the opening and closing of the aperture hole by a series of blades. These blades, when looked at closely, don’t create a perfect circle. Usually, they form a hexagon, octagon, or decahedron. The more blades you have, the closer it will be to being circular. With that in mind, the more aperture blades there are, the better. Lenses with nine or more aperture blades are usually more expensive than lenses with fewer blades.

But why is this important, you ask? Why would I want the opening of the lens to appear circular? Well, the answer to this lies in how the aperture affects bokeh.

How does the aperture affect bokeh?

First, let’s remind ourselves what bokeh actually is! Bokeh gets rather more publicity than it deserves, honestly. It’s basically the quality of the blurry parts of the image when you shoot at wider apertures. This can range from creamy gradients to little discs of light. Better lenses, that is, ones with more aperture blades, will produce smoother, more circular bokeh balls than lenses with fewer aperture blades.

In these images, you can clearly see the difference:

You only really get bokeh when shooting at wide apertures (or, of course, shooting with telephoto lenses, but that’s a whole other subject!). At f/16, all of the image should be in focus, so you won’t see any visible bokeh. At f/2.8, it’s a whole other story, however, and you will see a lot of bokeh.

What is the best aperture to use?

To answer this, we first need to know what you’re shooting. The subject matter determines the optimum aperture to use. Of course, these are merely a guide to get you started, and there is no hard and fast rule.

Best aperture for landscape photography

Generally, when shooting landscapes, you want to have the maximum depth of field possible. Think wide sweeping scenery, perhaps with mountains in the background and some nice foreground detail with leading lines drawing the eye around the image. We want it all in focus.

Now it depends on which lens you’re using, but let’s choose a nice ordinary 24-70mm lens. There are two options here: you can either choose f/11 or f/16 and be pretty happy with most of the image being in acceptable focus. Or you can use the hyperfocal distance rule and use f/8, setting your focus point to roughly one-third of the way into the scene. It’s a gross oversimplification, and we will go more in-depth into hyperfocal distance in another article. But that should get you within the right ballpark.

Best aperture for portrait photography

For portraits, it varies wildly depending on a number of things. Are you shooting natural light or with strobe? Is it an indoor or outdoor shoot? Are you going for a soft dreamy aesthetic or a hard fashion look? How many people are there?

All of these variations need to be taken into account. Now I like to shoot portraits with a 50mm lens, so we will use that as an example. If I want a softer natural light image with one person, then I might choose to shoot with an aperture of f/2.8. Any wider than this means that important parts of the image will be out of focus (like the eyes). I find f/2.8 creates enough bokeh while still having the entire eye in focus.

If I add a person and shoot a couple, I will increase my aperture to f/4 to make sure that both people are in focus. Similarly, a group or family, I will probably choose f/5.6 or f/8.

If I’m shooting in a studio with a strobe, I will generally start the shoot at f/8. Fashion images are usually shot with smaller apertures in this way, but of course, every general rule is there to be challenged, and you will always find exceptions.

Concert and performance photography

For music or concert photography, I would try to shoot as wide open as possible to let in the maximum amount of light. These are usually low-light conditions where you can’t use flash, and you’re often shooting handheld. This means a fast lens is a must. You’re usually shooting from a greater distance from your subject, which makes depth of field less of an issue. As always, it’s a trade-off.

Best aperture for macro photography

For macro photography, you are very close to the subject matter, which affects the depth of field. In order to give yourself the maximum depth of field, shoot with a tripod and a very small aperture. A minimum of f/16, but even f/22 if your lens will allow it.

Depending on your subject matter, you may even want to try focus stacking. If you’re focus stacking, then you want to take advantage of the sharpest aperture of your lens. For most lenses, this is around f/5.6 to f/8.

Best aperture for still-life photography

For still-life photography, it really depends on what effect you’re going for. However, most of the time, you will be shooting with artificial lighting, and certainly, for commercial product shoots or food photography, you will want the subject at least to be in full focus. You will again want to take advantage of the sharpest aperture for your lens, so choosing an aperture of f/8 is usually a good starting place. From there, you could try f/11 if conditions require.

How to change the aperture on your camera

To take advantage of the creative power of being able to choose your aperture, you have two main modes that you can use on your camera.

Av mode

The first one is the aperture priority mode (also called aperture value mode). You’ll see it labeled as Av or Ap on your camera. This is a great mode to start with if you’re just beginning to understand aperture because it is a sort of semi-auto mode.

Your camera will make all the shutter speed decisions and select the most appropriate ISO depending on the aperture setting you select. Care should be taken, however, if you choose a small aperture, the camera may choose a long shutter speed too long for hand holding.

Manual mode

Alternatively, you can select manual mode, which is usually labeled M. This gives you the most control over your aperture, ISO, and shutter speed settings. Depending on what your subject matter is, I would choose my settings in the following order:

1. ISO – select the most appropriate ISO for the conditions, similar to selecting a film speed in the old days of film.

2. Aperture – it makes the most sense to choose this next because it usually has more of a creative effect. The exception to this would be if you’re shooting fast-moving subjects or want intentional motion blur. In that case, shutter speed would be the second choice.

3. Shutter speed – it’s helpful to know how slow you can handhold each lens as a rough guide, and then if your settings fall slower than that, you have options. You can either open up the aperture to let in more light and keep your shutter speed higher, increase your ISO, or place the camera on a tripod.

So now you know all about aperture in photography. Aperture is important for determining both the depth of field in an image and the exposure.

Keep following along for the rest of the series.

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