What is Aperture in Photography?

What is Aperture in Photography?

Aperture is the size of the opening of your lens that light travels through to hit your camera sensor. If you’re a new photographer learning to take your camera out of auto, aperture is a setting you should master to learn how to correctly expose your photos.

Aperture controls exposure, how light or dark your photo is, and depth of field, how much of your photograph is in focus. Mastering it can help elevate your photography from good to great. Let’s take the mystery out of how to use the aperture setting on your camera so you can control the outcome of each shot, every time!

What is Aperture?

Aperture works a lot like the pupil of your eye–expanding and shrinking to allow more or less light through to your camera’s sensor. 

Like an eye, your camera lens has an iris that controls the aperture. Inside each lens is a set of blades that open or close to make the aperture wider or smaller.

Example of an aperture inside a lens. Many lenses have a maximum aperture opening of f/1.2-2.8 but some lenses have ultrawide maximum apertures, such as the Voigtlander f/0.95 lenses for Micro Four Thirds.

Aperture numbers (f/2.8, f/4, f/8, f/16, etc) are called f-stops. F-stops describe the size of the aperture, or how open or closed the iris of your lens is.

Now, this is the trickiest thing you’re going to read. It’s important to understand that the larger the f-stop number, the smaller the aperture. For example, an f-stop of f/32 results in a very small aperture, with a narrow lens, allowing very little light to enter.

In contrast, an f-stop of f/1.2 is a very large aperture, with a wide lens, allowing a lot of light to enter. This can be a confusing concept if you are a beginning photographer.

This chart shows how large an aperture opening is compared to its f-stop number. 

How Does Aperture Affect Depth of Field?

Have you ever framed up the perfect landscape shot, only to find that the trees were in focus, but the mountains and clouds were not? Or, have you wondered how to get sharp focus on the subject of a portrait, while achieving a beautifully blurred background? Depth of field is an important concept in photography and you control it with aperture.

Aperture numbers (f/2.8, f/4, f/8, f/16, etc) are called f-stops. F-stops describe the size of the aperture, or how open or closed the iris of your lens is.

By selecting your aperture, you can control how much of your scene is in focus. A large aperture (remember, this means a small f-stop) causes your lens to have a shallow depth of field. This means less of the scene is in focus. A small aperture (a large f-stop) will have a large depth of field. This means more of the scene is in focus at the same time.

An easy way to remember this is:

  • A small f-stop means a small amount of the scene is in focus.
  • large f-stop means a large amount is in focus.

The best way to understand this concept is to look at photographic examples:

girl-with-binoculars

Some lenses are designed specifically to enhance the effects of out-of-focus elements in a photo. The Sony FE 100mm f/2.8 GM STF OSS lens has an apodization element for extra smooth bokeh while Nikon’s 105mm f/2D and 135mm f/2D lenses have Defocus-Image Control Technology for better control of both background and foreground blur.

The above photo demonstrates an f-stop of f/2. The depth of field is so shallow, that even the woman’s face is out of focus. Shallow depth of field is useful for photos like this one, where the background would have been far too distracting if it were in focus (35mm, 1/100, ISO 100, f/2).

driftwood-beach

Depth of field is controlled not only by your aperture. The size of your sensor will also affect your final image. Learn more in How Crop Sensors Affect Depth of Field.

The above photo demonstrates an f-stop of f/16. This high f-stop resulted in a large depth of field, allowing both the subject in the foreground and the rocks in the distance to appear sharp (20mm, 1/45, ISO50, f/16).

How Does Aperture Affect Shutter Speed?

Your shutter speed is what freezes any motion in your picture. If you’re shooting a fast-moving subject, you may want to increase your shutter speed. This could, however, result in a photo that’s too dark or underexposed, since the shutter speed controls the amount of light that enters your camera.  

A slow shutter speed allows the waves to blur into a smooth haze. Learn more in Shutter Speed Chart and Tips on How to Master It.

On the other hand, you may need to decrease your aperture (remember, that’s a larger f-stop number) if you want to shoot a subject with a long exposure, or the photo might otherwise be overexposed.

rocks-with-sunset

Showing motion in water is essential and typically requires slower shutter speeds, which can overexpose your image. A smaller aperture increases depth of field and lets in less light to compensate when using slow shutter speeds.

This landscape was taken using f/16. Since that is a high f-number, it resulted in a large depth of field. The rocks are all in focus, even those off in the distance. The small aperture also allowed for a longer shutter speed, capturing the motion blur of the water without overexposing the scene (14mm, 3sec, ISO 100, f/16).

The Difference Between F-Stop and T-Stop

Now that you understand f-stop (higher number means smaller aperture and less light, lower number means larger aperture and more light, got it!), you’re probably wondering what a t-stop is.

Basically, if an f-stop is a measurement of how much light the lens is letting pass to your camera’s sensor, the t-stop is the measurement of how much light actually gets there. Wait, what?

Light has to pass through glass and is reflected before it gets to your camera’s sensor. Along the way, some of that light is lost. While it’s a small amount, knowing the t-stop is important. Matching the exposure from one scene to the next is essential–especially in cinematography.

T-Stops are an actual measurement of the light throughput of the lens since a small amount of light is lost as it passes through the glass elements. Put another way, F-Stop measuring relies on the size of the opening at the front of the lens whereas T-Stop is measuring the light that actually hits the sensor (the lens’ transmission).

Top cinema lenses will guarantee accurate real-world t-stop measurements. However, for a beginner photographer who is not shooting video, you will only need to focus on your f-stop number. The difference between an f-stop and the actual transmission (t-stop) is barely noticeable and you can easily correct any small differences between your photos by adjusting the exposure in post-processing.

Learn more in Photography vs Cinema Lenses: What New Videographers Need to Know.

Choosing Aperture

f/2, f/8, f/22, oh my! With so many f-stops to choose from, you’re probably asking yourself, where should I start? Don’t worry, there’s a method to knowing how and why to choose a particular aperture for your situation.

Before you press your finger on the shutter, you should know how important depth of field is in your shot. Once you make that decision, you’ll be able to decide which f-stop to choose. We’ve broken down general rules of thumb.

If you prefer a shallow depth of field with a soft, blurred background, you’ll need a large aperture. Then, you’ll only have a few f-stops to choose from, typically f/1.2 to f/5.6. An example of this is a portrait or a close up of a small object. Be aware that not all lenses go down to f/1.2 and may start at f/5.6 at their widest aperture. Longer lenses show this effect more dramatically. Part of that is because of subject distance, which is best explained in its own post.

aperture-girl-with-paint

This photo was shot with f/2.

If you need a large amount of your photo in focus, you’ll have a different set of f-stops to choose from–usually f/16 to f/32 and higher. An example of is this a landscape photo with greenery in the foreground and a mountain range in the distance.

aperture-flower-field

This photo was shot with f/20.

If the depth of field in your photo isn’t important, choose an f-stop between f/8 and f/11. Unless you’re trying to isolate your subject from the background, you won’t need to worry about depth of field. For example, if your subject is close to the background, like a person leaning against a wall, or if everything in the photo is in the same plane of view.

aperture-icy-doorway

This photo was shot with f/9.

How to Set Your Aperture

Typically, aperture is set with the dial on the top of your camera. Sometimes it’s controlled by a ring on the lens. Refer to your camera’s manual to set it.

Depending on what camera you use, you may also have the option of using Aperture Priority. This is a setting that allows you to choose your aperture and the camera will automatically determine the best shutter speed to give you a perfectly exposed photograph. This is a great stepping stone for beginners who don’t want to use auto but aren’t completely comfortable with going 100% manual yet!

Aperture is arguably the most important setting you’ll use. It controls both the depth of field of your photos and contributes to how well your images are exposed. While it may seem like a foreign language at first, master this setting and select lenses that offer the widest range of settings, to achieve the most creative control over your photography.

Shallow Depth of Field CC image courtesy of Chase Elliott Clark on Flickr
Large Depth of Field CC image courtesy of Steve Banfield on Flickr
Small Aperture and Slow Shutter Speed CC image courtesy of Azrul Nahar Zailah on Flickr
Aperture of f/20 CC image courtesy of Erika Gilraen Loss on Flickr

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1 Comment

  1. Great article!

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