Mastering the Basics: Aperture in Digital Photography


 
In optics, an aperture is a hole or an opening through which light travels. In Digital photography, this light is guided through to the sensor, which translates photons into a fixed image. However, aperture does a lot more than simply allowing light into the camera.


Like countless photographic pioneers, photographers today predominantly rely on shutter speed, aperture and ISO to control the outcome of an image in-camera. And while shooting in Auto mode is a useful option, harnessing the basic tools of exposure broadens the scope for creative photography. Here, we'll cover aperture, exposure, depth of field and bokeh. You'll find an in-depth look at shutter speed here.


Contents

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What is Aperture in Photography?

How it Works: the Aperture Mechanism

How is Aperture Expressed?

How Does Aperture Affect an Image?

How to Adjust Aperture on a Digital Camera

Automatic Scene Modes

Aperture, Shutter Speed and ISO

Aperture, Overexposure and Underexposure

How to Create A Shallow Depth of Field with Aperture

How to Create a Deep Depth of Field with Aperture

Aperture and Action Photography

Bokeh and Aperture

ICM Photography and Aperture

Aperture Settings for Blurred Moving Water Effects

Light Painting, Car Trails and Aperture

Aperture with Flash

Aperture Priority or Manual Mode?

When to Change Aperture Values

Frequently Asked Questions About Aperture



What is Aperture in Photography?

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Aperture is the adjustable opening inside a lens that controls the amount of light allowed to reach the sensor. The aperture is useful in several ways, it can control the brightness and darkness of an image, help prevent overexposure and underexposure and control the depth of field. Aperture can also adjust the amount of vignetting that occurs in an image.



How it Works: the Aperture Mechanism

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Positioned inside the camera lens, a device called a diaphragm opens and closes with the inputs made by a photographer or camera system. Much like the iris of an eye, the diaphragm itself is a thin opaque structure with an opening in its centre. The diaphragm stops the passage of light, except for the light that passes through the central hole or aperture. The aperture hole widens or shrinks depending on the setting selection made by the photographer or automatic camera system.



How is Aperture Expressed?

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Aperture is usually expressed as an f-number or f-stop. The f-number is the value assigned to every standard aperture diameter. Aperture values like f/2.8, f/5.6 or f/22 are shown on the LCD screen, rear monitor and through the viewfinder of a digital camera.



A smaller f-number denotes a greater aperture opening which allows more light to reach the image sensor, and restricts depth of field. A bigger f-number denotes a smaller aperture opening, which permits less light to reach the image sensor and allows for a greater depth of field.


Aperture selection is often described in terms of stopping down. Stopping down means increasing the numerical f-stop value (eg. graduating from f/2 to f/4). This decreases the size or diameter of the aperture of a lens, permitting less light and allowing a greater depth of field.


Lenses are also sometimes described as fast in terms of aperture. A fast lens delivers a wider aperture, which allows for more light in dark conditions. Fast lenses are more expensive, but they are ideal for situations involving portraiture and event photography. The Canon EF 24mm f/1.4L II USM Wide Angle Lens or the Nikon AF-S FX NIKKOR 24mm f/1.4G ED Wide-Angle Prime are two examples of fast lenses.





How Does Aperture Affect an Image?

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From atmospheric blur to pin-sharp renderings, aperture plays a key role in the outcome of a photograph. A wide aperture like f/1.4 for example, permits plenty of light through to the sensor. This is useful when using a faster shutter speed that inevitably limits light, which can often result in underexposure. On the other hand, when using a slower shutter speed that risks overexposure, a narrow aperture like f/11 will restrict the light reaching the sensor, helping to avoid washed-out images.



Action photography, which often relies on rapid shutter speeds, requires wide apertures to allow enough light to meet the sensor. This results in a balanced expression of frozen motion and acceptable exposure. A wide aperture is also useful in low-light conditions where gathering enough light is a priority. At the other end of the scale, smaller apertures often see use in ICM photography and other situations where a slow shutter speed is required, avoiding overexposure.


In addition to regulating light, aperture selection also dictates the depth of field (DOF) - the range of distance in a photographic image that appears acceptably sharp. A shallow depth of field means that only a small amount of subject matter appears in focus in an image while a large depth of field describes a broader field of sharpness. In other words, more aspects of an image will be sharp with a numerically larger f-number.


How to Adjust the Aperture on a Digital Camera

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Just like shutter speed, there are two main modes that allow for the manual manipulation of aperture in-camera. Aperture Priority is a semi-automatic shooting mode - it permits the photographer to select an aperture setting while the camera detects and sets an adequate shutter speed. In this mode, ISO sensitivity can be set to automatic or manual. Aperture Priority is usually abbreviated as A or AV on the mode dial.


The second way to manually control the aperture is to work in Manual mode. Manual Mode allows a photographer to take full control over shutter speed and aperture at the same time. Manual mode is typically signified by an M on the mode dial.



Changing Aperture on a Canon Camera


AV mode (Aperture Priority) and M (Manual mode) are activated via the mode dial. Switch the mode dial to AV and the aperture value can be adjusted by turning the main dial while the shutter speed adjusts automatically for an acceptable exposure.


For manual mode, switch the mode dial to M. Different Canon cameras can have different exposure mechanisms. On a 5D MKIV for example, in manual mode, scrolling the main dial changes shutter speed and the quick control dial changes aperture. Other Canon models may require a user to select Manual exposure mode and press and hold the asterisk button while scrolling the main dial simultaneously to adjust the aperture. On many Canon cameras, the aperture can also be adjusted on the rear touch screen. The active aperture appears on the LCD panel, through the viewfinder and on the rear screen.



Changing Aperture on a Nikon Camera


To adjust the aperture in Manual mode on a Nikon camera, first rotate the mode dial to M. Shutter speed is selected by rotating the command dial. To adjust the aperture value, keep the Adjusting Aperture button depressed while rotating the command dial. To activate Aperture Priority Auto, switch the mode dial to A. Then, rotate the command dial left or right to select an aperture.


Changing Aperture on a Sony Camera


To put a Sony camera into Manual or Aperture Priority, turn the mode dial to M or A respectively. Then, turn the main dial left or right to increase or decrease the aperture value.




Automatic Scene Modes

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In addition to Manual and Aperture Priority Modes, many cameras also offer scenario-specific camera settings. These automatic scene modes typically include presets designed for action, portraiture, night portraiture, landscapes and/or macro photography. For example, in Portrait Mode, the camera aims to select an aperture setting that pushes the background out of focus while keeping the main subject sharp. However, although these presets are handy, they can often fall short in unique situations where Manual and Aperture Priority modes are more flexible.


Aperture, Shutter speed and ISO

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Besides aperture, shutter speed and ISO are the other two staples of any exposure. ISO defines the amplification of data received when light reaches the sensor. A higher ISO value contributes to a brighter image. However, the higher the ISO value, the noisier or grainer the digital photograph.


The shutter speed controls the duration a shutter mechanism is open in the camera, dictating how much light meets the sensor. The longer the shutter speed, the more light is allowed to impact the sensor, creating a brighter image. In addition, the shutter speed controls the manifestation of movement in a photograph - a longer exposure captures more motion blur, while a fast shutter speed results in frozen motion.

When manually adjusted, ISO, aperture and shutter speed all work together to capture images with more authority than in Auto mode. This can be ideal if a photographer needs to manipulate different aspects of an exposure to achieve a specific effect. For example, in ICM photography in daylight, a photographer may shrink the diameter of the aperture and decrease the ISO value to help minimise overexposure in bright conditions.


Aperture, Overexposure and Underexposure

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Overexposure occurs when an excessive amount of light makes contact with the sensor, creating overly bright images. For example, in well-lit situations, a wide aperture can result in overexposure. However, boosting the shutter speed, closing the aperture down and/or reducing the ISO are three key ways to combat overexposure. In addition, using a Neutral Density (ND) filter is also useful for cutting down on light when a wide aperture and/or long exposure is required.



Underexposure, the opposite of overexposure, can occur if conditions are dark, when the aperture is too narrow and/or the shutter speed is too fast. This can create undesirably dark images. To fix underexposure, shoot at a slower shutter speed, boost the ISO value and/or open the aperture to capture more light. The addition of flash will also create illumination in dark conditions.


How to create A Shallow Depth of Field with Aperture


In photography, depth of field describes how much of the image is in focus. A very shallow depth of field creates isolation by surrounding a subject with blur in the foreground and/or background. This helps to guide the viewer's' eye and creates atmospherically dense renderings of a scene.



In photography, a shallow depth of field is achieved by taking photographs with a low f-number ranging from f/1.4 to about f/5.6. Depending on the subject matter, photographing subjects at these settings can blur the background and/or foreground of the image, highlighting a central subject. However, due to the nature of wide apertures, a faster shutter speed and low ISO value may be required to prevent overexposure.


How to Create a Deep Depth of Field with Aperture



A deep depth of field is created with narrower apertures (or big f-numbers) to exhibit a greater rendering of sharpness, meaning most or all of a photograph will be in focus. This is often exploited in landscape photography and group portraiture situations where the foreground and background must be consistently sharp. However, a narrower aperture can also be handy in macro photography - maintaining a greater degree of sharpness in small subjects.


Apertures ranging from f/16 are generally considered to render a deeper depth of field, but due to their narrowed diaphragm, they also cut down on the light reaching the sensor. Because of this, numerically higher f-stop settings and are often paired with a slower shutter speed and a higher ISO value to compensate for the restricted amount of light. In addition, tripods or monopods are sometimes used with narrow apertures, steadying the camera for longer shutter speeds.




Aperture and Action Photography

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Active subject matter often demands rapid shutter speeds. But to capture or freeze a fast-moving subject with as little blur as possible, shutter speeds of up to 1/8000s may be necessary. Because a rapid shutter speed cuts down on the amount of light that reaches the sensor, a wide aperture selection will help maintain a suitable exposure. Wide apertures like f/2.8 also separate the subject from a background, creating a more dramatic rendering of motion.




Bokeh and Aperture

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Bokeh is a Japanese word that translates to English as haze or blur. Bokeh is defined as the way a lens renders unfocused points of light in an image. Depending on the subject matter, equipment and camera settings, this effect ranges from illuminated dots to dreamily unfocused backgrounds.



When it comes to capturing bokeh, a fast lens is ideal – that is, a lens with an aperture of f/2.8 or wider. The AF-S NIKKOR 70-200mm f/2.8E, the AF NIKKOR 50mm f/1.8D, the Canon RF 50mm F1.8 STM or the Sony FE 135mm f/1.8 GM are a few popular lenses for achieving silky bokeh effects. Smooth bokeh is particularly sought after by users of macro lenses and long telephoto lenses because they are typically used in scenarios that require a shallow depth of field.



To maximize the bokeh effect, shoot in Aperture Priority or Manual mode with an aperture set to f/2.8 or wider. Depending on ambient light conditions, a faster shutter speed and a minimal ISO value may be required for an adequate exposure. If possible, use a long focal length and increase the distance between subject and background to exaggerate the bokeh effect, seeking out specular highlights like lights and reflections. Some filters can also be fitted to the camera lens to create bokeh in the shape of hearts, crosses or swirls etc.





ICM Photography and Aperture

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ICM stands for Intentional Camera Movement. By selecting a slower shutter speed and physically moving the camera during exposure, ICM photographers create intricate abstract renderings of both moving and static subject matter. A shutter speed above 1/125 will reduce blurred motion, so ICM photographers often maintain a shutter speed below 1/15. Depending on the surrounding conditions, a narrower aperture setting may be necessary to reduce overexposure.


Aperture Settings for Blurred Water Effects

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Blurred water effects are popular in landscape photography. However, although the blurred rendering of water is generated through the application of a longer shutter speed, a narrow aperture serves as the mechanism to maintain a broader depth of field throughout the image and regulates the amount of light reaching the sensor.



For a blurred water effect, set the shutter speed to around 1/15 in Manual mode. Next, adjust the aperture to around f/11. From there, make a few test shots and incrementally adjust the balance of aperture and shutter speed. The longer the exposure, the more blurred the moving water will appear. However, for very prolonged exposures in bright conditions, an ND (Neutral Density) filter may be necessary.


Light Painting, Car Trails and Aperture

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Light painting and car trail photography are two ways to make creative use of bright lights in dark settings. Light painting involves recording a moving light source over the duration of a long exposure. Sparklers, flaming steel wool, torches, glow sticks, fire poi and LED lights are all good sources of illumination for light painting.


Car trails are captured as cars pass through a landscape at night. A photographer sets up a camera near a roadway and uses a long exposure to record the glowing headlights and tail lights of travelling cars and trucks. Aircraft lights or bike lights can also be photographed at night to a similar effect. In both light painting and car trail photography, a combination of a long shutter speed and an aperture of around f/8 or f/11 is ideal.




Aperture with Flash

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A flash provides a burst of light that lasts for a fraction of a second. The light emitted from a flash can be used to compensate for the lack of brightness when shooting in dim environments, enabling the use of narrow apertures and the ability to freeze motion.


In flash photography, the shutter speed affects the amount of ambient light captured in an image, while the aperture is the main mechanism that controls the brightness of the flash. The narrower the aperture diaphragm, the less pronounced the flash effect with be. The wider the aperture, the brighter the flash.




Aperture Priority or Manual Mode?

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Aperture priority and Manual mode are two critical exposure modes available in-camera. In Aperture Priority, the shutter speed is automatically adjusted for adequate exposure depending on an elected aperture setting, which is often useful for capturing fleeting subject matter. However, sometimes a greater degree of control over exposure is required. Manual mode provides a photographer with the ability to toggle both the aperture and shutter speed individually, allowing for greater command over the camera overall. Manual mode is more versatile in unique circumstances like high or low contrast scenarios, though it can be slower to set in a rapidly evolving environment. Put simply, Aperture Priority is faster to set and can ease the workload on a shoot.


When to Change Aperture Values

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The signal to change aperture lies in the desired outcome of a photograph, the surrounding environment and the technical constraints of the camera. If a test shot looks undesirably dark, it's a cue to either set a longer shutter speed or open up the aperture diaphragm. If a test shot looks overly bright, adjust to a shorter shutter speed and/or narrow the aperture diaphragm. If a greater depth of field (less blur) is desired, narrow the aperture a few stops. If a shallower depth of field is needed (more blur), open up the aperture by a couple of stops.


Frequently Asked Questions About Aperture

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Q: Why does Aperture matter?


From ICM to macro photography, aperture is important for both technical and creative reasons. Along with shutter speed, the aperture regulates the brightness/darkness of an image. Aperture also dictates the depth of field in an image, or how much of a scene is in focus. The larger the aperture diaphragm, the brighter the image and the less depth of field. The narrower the aperture diaphragm, the darker the image and the greater the depth of field. These parameters can be exploited for creative purposes -a large depth of field conveys grand vistas, while a narrow depth of field creates an effect that guides the viewer's eye.



Q: Why are my images too Bright/white/washed out?


When an image is too bright or washed out it means the picture is overexposed. Overexposure can often be caused by selecting an overly wide aperture or a lengthy shutter speed. To reduce the effects of overexposure, increase the shutter speed to cut down on the light that reaches the sensor and/or shrink the aperture to allow less light through during an exposure. In addition, you can reduce the ISO sensitivity, target more subtle lighting conditions or use an ND filter.



Q: Why are my images too dark/black?


A photograph that looks too dark or black is underexposed. This occurs when too little light reaches the sensor during an exposure. Working in dark conditions, selecting a narrow aperture setting and/or a fast shutter speed cuts down on the light entering the camera, causing darker images. To combat this, open the aperture to permit more light (eg. f/5.6 to f/2.8) and/or increase the duration of the shutter speed (eg. 1/250s to 1/125s). Using flash or increasing the ISO value can also help brighten an image.


Shutter speed article on IRIS28 - an example of exposure, underexposure and overexposure on a mandarin


Q: How does ISO affect Aperture?


In digital photography, the ISO value refers to the signal gain from a camera's sensor. A low ISO rating (eg. ISO 100) results in a darker image than a higher ISO rating (eg. 1000) This means that a higher ISO value can help contribute to brighter images, compensating for a narrower aperture selection. The trade-off is that higher ISO values create more noise or grain in an image, which can sometimes appear disruptive.


Q: How does Aperture affect depth of field?


Aperture has a direct impact on depth of field. DoF is the zone within a photograph that is acceptably sharp and in focus. A shallow depth of field has a small depth of focus, whilst a deep depth of field exhibits a more uniform sharpness throughout the photograph. The degree of focus within a given image is dictated by the aperture. For example, a very narrow aperture like f/16 will maintain focus across a scene, while a larger aperture like f/2.8 will create a significant amount of blur around the focal point in an image.


Q: How does Aperture affect Motion blur?


Shutter speed dictates how subject movement and camera motion appear in a photograph. The slower or longer the shutter speed, the more motion blur manifests in an image. Aperture affects the depth of field in an image, leaving shutter speed to render motion. However, the longer shutter speeds required for pronounced motion blur can flood a camera sensor with excessive amounts of light, leading to overexposure. To help alleviate this issue, a narrow aperture can be selected to restrict the amount of light reaching the sensor.




Q: What should I set my Aperture to?


Aperture is determined by many variables. It's impossible to choose the one setting to cover every individual event or scene. That said, there are some settings to use as a reference point in some scenarios. For example, many landscape photographers initially select a narrower aperture like f/16 to photograph landscapes, making use of a larger depth of field to maintain focus.