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How to Learn Photography: Understanding Aperture

Understanding aperture is a cornerstone of learning photography. Part of the exposure triangle, it’s one of the most essential concepts in photography. Choosing to learn the technical side of photography will allow you to control and command your camera, no matter what kind you use or for what purpose. What does aperture do? The short answer is: it controls light entering the camera and how much of the image is in focus.

close up of lens aperture to help understanding aperture in photography

This post is a deep-dive, so if you’re short on time or have the attention span of a goldfish (like me), use the table of contents to jump around and save this for later. The most essential information about aperture begins with What is Aperture through What Aperture Does When Taking a Photo. The sections after that have info that is still important as you learn photography but can save for later.

What’s the TLDR of aperture and its relationship to exposure?

Aperture is set by the camera’s lens, and determines how much light comes through and how fast. A large aperture size = more light & less depth of field. A small aperture size = less light & more depth of field.

If you’re brand new to photography beyond point and pray, take a minute to go through the Aperture Glossary before reading on.

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What is Aperture?

Aperture is a function of the camera lens – a circular opening (diaphragm) made of “blades” that determines how much & how quickly light reaches the sensor when the shutter opens. 

The blades vary in number –  most commonly 5 – 9 and may be straight or curved. More blades and curved will typically result in a smoother out of focus area.  The visual quality of the out of focus area is called bokeh. The aperture setting of a lens is indicated as the f/stop, such as f/2 or f/16. 

Your camera has a shutter (mechanical or electronic), which opens in order to expose the sensor to light when taking a photo. This controls shutter speed, and is measured by fractions of a second: 1/500th (a fast shutter speed) for example, or 20 seconds in the case of a long exposure. 

Shutter speed is a function of the camera body, independent from the lens. From smartphones to top of the line professional photography equipment, these two functions remain separate.

close up of a camera shutter
A mechanical camera shutter; many cameras use an electronic shutter which has no moving parts. Both have advantages and disadvantages but don’t affect aperture or depth of field.

This is part one of a 4-part photography basics series: Aperture, Shutter Speed, ISO, and The Exposure Triangle. Be sure to subscribe to receive notifications as each part is published.

What Do the Numbers Mean in Aperture?

Almost all lenses (whether a separate detachable lens or one fixed to the camera) have an aperture range. For example, you may have seen this designated in the description or on the lens as “f/2 : f/16”.  This means the lens aperture can be changed from f/2 all the way through to f/16.

A fixed aperture means the lens has just the one aperture setting and it cannot be changed – this is the case on some smartphones and vintage lenses. But just what do the numbers mean in aperture?

A small aperture size is represented by a larger number, whereas a large aperture size is represented by a smaller number. Setting your aperture to a larger size is called opening up. Setting your aperture to a smaller size is called stopping down. A large aperture size is also referred to as wide, whereas a small aperture size is referred to as narrow.

infographic demonstrating aperture in photography

Two common photography phrases you’ll hear refer to changing the aperture: stopping down or opening up. “I stopped down my lens from f/4 to f/8” or “I opened up my lens from f/16 to f/2”

How Does Aperture Affect a Photo?

Aperture size affects two elements in photography: light gathering and depth of field (DOF). Aperture is the only photography setting that affects your depth of field – shutter speed and ISO do not affect DOF. 

When taking the photo light gathering is the key function of aperture and affects exposure. Depth of field is part of the result but affects the look of the actual photo. It does not impact exposure.  

comparison photos of shallow depth of field and deep depth of field
On the left a small aperture creates greater depth of field. On the right a large aperture results in very shallow depth of field.

As mentioned above, setting the aperture size affects the quantity & speed of light hitting the sensor when the shutter opens. When choosing an aperture setting, you’ll need to consider whether more or less DOF is desirable as well as the ideal shutter speed and ISO settings for a successful photo.

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What Aperture Does When Taking A Photo

Aperture and Exposure

Think of it as a two lane road versus an eight lane highway. With a wide aperture, more light can get through vs with a narrow aperture letting less light through. An eight lane highway allows more cars to arrive at a destination than a two lane road would in the same amount of time. A narrower aperture has less light coming through, much like a narrow country lane only allows one vehicle at a time so more time is needed to reach the destination.

Aperture is one of the three elements of the exposure triangle, one of the most important concepts to understand in photography. Changing your aperture changes how much light is able to reach the sensor. If you change an aperture setting, and don’t want your photo’s exposure to change, you will also have to change at least one of the exposure triangle elements.

This can be done manually (called shooting in full manual) or using Aperture Priority mode on your camera, allowing the camera to adjust shutter speed and ISO automatically.

Aperture and Depth of Field

The other aspect of your photo affected by the aperture is the depth of field. Depth of field is the amount of the scene that is in focus. A wide aperture has a shallow depth of field whereas a narrow aperture has much greater depth of field. An example of shallow DOF is a close-up portrait, where just the face is in focus but the background is softly blurred. A deeper/wider depth of field is most often used in landscape photography, where it’s desirable to have as much of the scene in focus and sharp as possible.

portrait of a woman using wide aperture to create shallow depth of field compared to landscape image using a narrow aperture to create greater depth of field
L: a wide aperture of f/1.8 creates appealing blur in the portrait. R: a narrow aperture of f/16 was used to achieve the greatest DOF possible, keeping both the foreground and distant rock formation in focus


How Focal Length Impacts DOF

Understanding how lens focal length impacts DOF is a bit more advanced. This is the part of aperture that impacts the look of your image rather than the exposure of it. Pause here if you’re starting to experience information overload.

The focal length of a lens does not change the brightness of an aperture setting. F/4 has the same brightness on a 35mm lens and a 135mm lens. Focal length is not part of the exposure triangle, so don’t worry about different focal lengths impacting your exposure.

However, depth of field is also affected by the lens focal length. When referring to length, it’s not the literal length of the lens. The millimeter measurement is the distance from the camera sensor to the optical center of the lens.

So two different 35mm lenses may have different overall length but that distance is still 35mm in both. Lenses can be super wide, wide, normal, telephoto, or super telephoto. A lens’s focal length is indicated in millimeters.

***Sensor Size & Focal Length***

An important note about focal length and sensor size: all focal lengths here (and in photography generally) refer to a focal length on a “full-frame” or 35mm size sensor. This means that a 35mm lens on a full-frame sensor (like the Canon EOS R6 or Sony A7C) will become 53mm on a crop sensor (like the Fuji XT-5 or Sony A6400).

On a full-frame camera 16mm is super wide but on a crop sensor (like my Fuji XT-4) it’s 24mm and just a plain old wide angle. To get the full frame’s 16mm angle of view, I’d need a 10mm lens. This is called the effective focal length: my 16mm lens has an effective focal length of 24mm.

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Wide Angle, Super Wide, and Fish-Eye Lenses

A wide angle lens is a “short lens”, and has the largest angle of view. Examples of common wide lens scenes are sweeping landscapes or architectural photos that take in a whole room or building from close up. Lenses from about 16-25mm are considered wide; anything less falls in the super wide or fisheye category.

L: a fish-eye lens creates distinctive distortions with its extreme wide angle of view. R: a more natural image with minimal distortion using a regular wide angle lens

Normal Lenses

Normal lenses from about 35mm to 70mm fall in the normal category. These are good all-purpose focal lengths for many types of photography. 35mm and 50mm are the most commonly used normal focal lengths, partly because they most closely replicate our normal field of vision (not including peripheral).

historic center of rome, people at a cafe outside, photographed using a 23mm fujinon lens
Using a 23mm lens on the Fuji X-T4 results in a 35mm effective focal length, the wider end of the normal focal length range
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Telephoto and Super-Telephoto Lenses

Telephoto and super telephoto lenses allows taking a close up photo of a distant objects, such as the moon or very small detail on a far away building. Telephoto lenses (sometimes also called medium telephoto) go from about 85mm to 300mm. Beyond that is the super telephoto category – these are quite large in size and often very expensive. A top of the line super telephoto of 800mm can cost upwards of $10,000!

budapest skyline at dawn in shades of pink
Using a focal length of 240mm (effective length of 360mm) allowed me to get a close-up image of far-off buildings in Budapest

Zoom Lenses vs Prime Lenses

Many people use the term zoom lens when they mean long or telephoto lens – which of course refers to the angle of view. Zoom means a lens that changes focal lengths – you can have a wide angle zoom, a telephoto zoom, or a standard zoom. A lens that does not change focal length (no zoom) is called a prime lens. One is not inherently better than the other and both have pros and cons depending on your needs, experience level, and budget.

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Advanced Aperture and DOF: Focus Distance + Focal Length

So how do lens focal length and focus distance affect depth of field? Well, there’s a physics explanation for this but you don’t need to understand physics to grasp the relationship between aperture, focal length, and depth of field. There are resources that explain the physics behind focal length and aperture that can be helpful if you understand those topics well.

DOF is affected by both the focus distance and the focal length of the lens. Again, this is explained by physics but understanding physics isn’t needed to understand the result. Know that the closer your subject of focus is, the shallower the DOF of a given aperture. A longer lens will make it easier to create shallow DOF but harder to create a deeper DOF. Inversely, a wider lens makes deep DOF easier but shallow DOF harder.

Aperture and Focus Distance 

The distance from the camera sensor to subject is your focus distance. No matter the lens focal length, a closer focus distance at a given aperture will have less DOF than a farther focus distance. In the example below, you can see that a 50mm lens set to f/4 and focused on a subject 2 feet away has a DOF of 0.92 inches. But change the focus distance to 6 feet and the DOF is now 8.28 inches.

DOFC photography app screenshots demonstrating how focus distance affects DOF at a given aperture and lens length

Aperture and Lens Focal Length

Now let’s look at two different focal lengths: 35mm and 85mm using the same aperture (f/4) and same focus distance of 4 feet. With the 35mm lens, the DOF will be 7.53 inches. But with the 85mm lens, the DOF will be 1.27 inches. Of course the framing will be different. The wider 35mm lens will include more of the scene in front of the camera, while the 85mm lens will include less of the scene.

screenshot of DoFC app showing how depth of field differs with lens length

This can seem overwhelming, and you will eventually gain the experience to account for these factors without thinking about it. While you learn, you can use a depth of field photography app that allows you to enter the focal length, aperture, camera sensor type, and focus distance. 

It will then show the resulting depth of field, and you can make adjustments from there. It will also provide the hyperlocal distance, which is the focus distance that achieves the greatest possible depth of field from that point towards infinity.

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Which Camera Mode to Use

More advanced cameras will have the option of modes to choose from. Some are completely pre-programmed for specific situations. Common modes are Portrait, Landscape, Night, and Sport. This is when the camera selects all the exposure triangle settings for you – shutter speed, aperture, and ISO.

close up of digital camera mode dial
Av = Aperture Tv = Shutter M = Manual P = Program. Depending on the camera manufacturer, other mode settings will vary. Here are common scenes like Portrait, Landscape, Sport, and Night.

However, when aperture is your most important setting you’ll want to choose Aperture Priority Mode – usually marked on the mode dial as A or Av. This means that you choose the desired aperture, allowing the camera to adjust the shutter speed. You can also choose auto ISO to fully automate these two elements. Some of these settings may or may not be available on all cameras, but they are on most.

Personally, I do not like to use auto ISO, and will also adjust that manually as needed. The only setting adjusted by my camera is the shutter speed. If it drops too low, I can adjust my ISO or aperture accordingly. 

Shooting in full manual is a more advanced option requiring more experience and attention. Full manual means you choose all three exposure triangle settings: aperture, shutter speed, and ISO. If nothing about the scene you’re shooting is changing – like in a studio with artificial lighting – manual would be the best choice. Out in the real world, especially in travel photography when conditions can change rapidly, choosing aperture priority or shutter priority will almost always be the better fit.

If you are shooting with a phone camera, the native camera app may allow changing these settings or you will need to choose a photography app that allows you to make those adjustments yourself instead.

How to Choose the Right Aperture

Once you understand how aperture works, the next step is learning how to choose the right aperture for your photo. There are three main considerations in this decision process. The right aperture is the one that allows you to achieve your creative goals within the technical needs of the situation.

  1. How much DOF do you need? This will depend on your subject. If you want a landscape with as much DOF as possible, you’ll need a very narrow aperture (a deep DOF) such as f/16 to achieve that. Or, if you want a nice blurred background to drive the attention to your subject (a flower, a person), you’ll want a wide aperture (create shallow DOF) such as f/2.
  2. What lens are you using? If you’re using a very wide lens, such as a 16mm with a maximum aperture of f/4 it will be much harder to get a shallow DOF than with an 85mm lens with a maximum aperture of f/1.8. Understanding the relationship between focal length, subject distance, and aperture is critical here. It’s how you know whether you can achieve the desired result with the equipment at hand.
  3. How does the aperture setting affect the exposure triangle? As mentioned above, your aperture is one of the 3 exposure triangle elements. If you need a fast shutter speed AND lots of DOF, you’ll need to raise the ISO maintain correct exposure. If you are shooting in aperture priority mode, most cameras will let you set auto ISO as well. This means the camera will adjust the shutter speed and ISO accordingly. You can also shoot full manual mode – you choose all 3 settings – which is a more advanced and nuanced technique.
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What Aperture Setting is Best for Travel Photography?

Because travel photography involves many genres, there is not one single “best” aperture for travel photography. There are common situations and scenes though, with an ideal starting aperture. You can then adjust the aperture based on the exact situation or your personal preference. Of course there are exceptions, so take these as a starting point in your travel photography journey.

What Aperture is Best For Street Photography

For street scenes f/5.6 – f/8 is broadly considered the ideal aperture range to work with. When using wide to normal focal lengths – 24mm to 50mm – this allows for a moderate depth of field. This allows the photographer to work quickly and be responsive to the moment.

What is the Best Aperture for Landscape Photography

Landscape photography is the realm of expansive depth of field. Typically f/11 – f/16 will be an ideal range. Most lenses are at their sharpest when stopped down, but going beyond f/16 can result in a effect called diffraction, which reduces sharpness in the image. Because landscape photography often takes place in lower light with a narrow aperture , a tripod is needed to obtain the sharpest image. This allows for the lowest ISO setting (the least amount of “noise” or grain), a long enough shutter speed for correct exposure, and the narrowest aperture setting.

What Aperture is Best for Travel Portraits

Classic portraits typically use a longer lens, from about 70mm to 135mm and often use a shallow depth of field to keep attention on the subject. At those focal lengths the aperture will be set as low as f/1.4 to about f/5.6, depending on how close up the portrait is. 

Travel portraits are a little different, because it often adds to the image to have the background just a bit more in focus to provide context or a sense of place. A slightly shorter lens range may also be used, from about 35mm to around 85mm. In this situation an aperture of about f/2.8 to f/5.6 will blur the background enough to create good separation of the subject from the surroundings, but not so much background blur that there’s no sense of place.

What Aperture is Best for Food Photography?

Food photography is a little bit like portrait photography – a shallow depth of field and flattering lighting are reliable choices for appealing food images. 

Photographing the food from your travels often means less than ideal surroundings. If you want all the attention on the food, use a wide aperture, f/2.8 to f/4 – this will blur out distracting or unattractive backgrounds but keep most of the food in focus.

If you would like to capture the environment around the food, stop down a bit more. Choosing an aperture of f/4 to f/6.3 will typically show off the environment while still highlighting the food.

What Aperture is Best for Travel Photography at Night?

For overall street scenes where you want to avoid too much motion blur, an aperture of about f/2.8 – f/5.6 will work in many situations. If you have a tripod and don’t mind a lot of motion blur from moving pedestrians or vehicles, you can stop down to f/8 – f/11.

You can also take creative portraits at night, using shop lights, neon signs, and other nighttime illumination to great effect. Careful attention to focus will be necessary, but using the shallowest possible aperture of f/1.2 – f/4 will render the background lights as blurs of color.

What Aperture is Best for Night Skies?

Night sky photography is a challenging but rewarding niche of landscape photography. True astro photography requires patience, careful planning, and proper equipment and post-processing technique. It also often does not include much of the landscape at all.

Night sky landscape photography is still possible with good quality camera equipment – and a tripod. Star trails are a little bit easier, and can be captured with a wider lens set to an aperture of about f/7.1 to f/11

To achieve a night sky photo without start trails – rendering the stars as points – you’ll need a wide angle lens, high ISO, and an aperture of about f/2. Because star trails begin to occur in as little as 20 seconds of exposure, a wide angle lens, bright aperture, and high ISO are all needed.

Understanding Aperture Glossary


The visual quality (not quantity) of the out-of-focus part of an image. Typically a very smooth, graduated bokeh is most desirable, and some photographers get a bit obsessed with this. Vintage or specialty lenses may have very distinctive bokeh. You may hear the term “nervous” bokeh. This means the the blurred area may have odd rings, striations, or swirls and is generally not desirable.


Refers to either the aperture setting (a wide aperture like f/2) or the maximum aperture of a lens. Lenses with a very wide maximum aperture (usually 2.8 or wider) are called “bright” lenses.


Depth of Field – the portion of the image that is in sharp focus. Shallow or narrow depth of field = a small “slice” in focus. Wide or deep depth of field = a large portion of the image is in focus.


The aperture setting: f/2, f/5.6, etc. On the front of a lens the f/stop range will usually be shown as 2.8/22 – or whatever the maximum and minimum apertures are on that lens.

Focal Length

Focal length refers to the lens only. Measured from the optical center of the lens to the camera’s sensor in millimeters. The total length of the lens will vary some based on other factors. So, a 50mm lens from 3 different brands may have different lengths, but the distance from the optical center to the camera sensor will be 50mm in all three.

Lenses may be referred to as short, medium, or long (such as a 16mm, 50mm, or 200mm) or wide/normal/narrow because of the field of view.

Opening Up

This term refers to changing the aperture to a wider one. Going from f/8 to f/4 would be “opening up” the lens

Stopping Down

Simply the opposite of opening up, stopping down a lens would be going from f/4 to f/8

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  1. Ryan R Richter

    Very well put together! It’s a lot to take in but I hope I can utilize it to get some great shots on my Euro trip this summer! Memories are great but framing one would be even better.

    Thank you for the great article and info!

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