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What is aperture in photography?

Beyond the technical aspect of controlling light that passes through a lens during an exposure, aperture also has a number of aesthetic consequence

What is aperture in photography?

The photographer’s eye is often what lies at the heart of a photograph, and lenses are the medium that translate vision. In that respect, it’s no surprise that the lenses on our cameras share quite a bit in common with the very eyes that guide them. Just as our pupils open wide as we navigate a dark room and contract in bright afternoon sun, so do lenses as we photograph. In photography this mechanism is known as aperture – it’s the ‘pupil’ inside your lens that controls how much light passes through. If you think about the light that creates a photo as a constant flow of water, shutter speed is how long you have the spigot open, and aperture the width of the hose.

Beyond the technical aspect of controlling the volume of light that passes through a lens during an exposure, aperture also has a number of aesthetic consequences that photographers can creatively leverage or manipulate in tricky lighting conditions. Whether creating a softly blurred background in a tightly composed portrait, or maintaining sharp detail that expands from the foreground to the background of a landscape photograph, aperture is a critical consideration when matching your mind’s eye to a photographic composition. The best way to learn about aperture is to adjust it yourself and see how you can use it to match your own personal style and vision.

Adjusting aperture

The easiest way to play with aperture without getting lost in other exposure settings is with aperture priority mode. Most cameras, from point-and-shoot to advanced DSLRs, will have aperture priority mode on their primary mode dial or menu – look for the ‘A’ or ‘Av’ label, just don’t confuse it with your camera’s ‘auto’ mode. Once set on aperture priority, you should be able easily change aperture with your main adjustment dial. What makes this mode ideal for learning about aperture is that once you select your f-stop (the number that represents a specific aperture setting), your camera will automatically set an appropriate shutter speed.

When experimenting with aperture priority mode, it is helpful to see how adjusting aperture interacts with exposure – so even though you don’t have to adjust the shutter speed, it’s a good practice to look through your viewfinder or display to see how it shifts. For example, if you take a picture with your aperture set to its widest setting (the lowest f-stop number), and another at a higher f-stop, you’ll notice your camera automatically slows its shutter speed for the higher f-stop image. Higher f-stops let in less light (creating a darker exposure), so a slower shutter speed compensates for this by increasing the amount of time that light passes through. This balancing act between aperture and shutter speed is critical to understanding how exposure works. Admittedly, aperture can be a little counterintuitive at first because the lower the f-stop, the more light the lens lets in. 

Getting to know your lens

The range of f-stops available for you to use depends on your specific lens. Many standard kit lenses have a low aperture of f/3.5 or so, while higher end lenses may go as wide as f/1.4 or wider. Prime lenses (lenses that don’t zoom) make wide apertures more accessible by nature of their design, so if you want an affordable DSLR or interchangeable lens that also has a wide aperture, consider something like a 50mm f/1.8 – if you want to go wider you’ll usually end up paying significantly more for f/1.4 models. The wide end of the aperture range is often what is advertised and labeled on lens listings, as low light can be a limiting factor in many shooting scenarios and that extra f-stop or two on the low end can often make a big difference. Most lenses on the market today have a maximum standard aperture of f/22. A ‘standard’ or ‘normal’ prime lens in the 35mm to 50mm range is a great place to start when experimenting with aperture, and because they don’t zoom you’ll often become more aware of your composition (and its limitations) – zoom with your feet!

Depth of field

In line with exposure, the other prominent effect of aperture is known as depth of field. The best way to think about depth of field is to imagine an adjustable slice of ‘in focus’ space parallel to your lens. A shallow depth of field makes this slice very narrow, keeping only a small sliver of space in focus. A deep depth of field equates with a larger area of in focus space. The wider your aperture, the shallower your depth of field becomes. For example, if you want to isolate your subject against a blurred background, use an aperture setting of f/2.8 or wider for this shallow depth of field effect. In contrast, if you want your composition to maintain focus from the foreground to the background, use an f-stop of f/8 or higher.

Other factors that influence depth of field include your lens’ focus length (the ‘zoom’ of your lens) and your physical proximity to your subject. Higher focal length lenses that magnify the world around you will inherently have a shallower depth of field, as will getting in close to your subject. The best example that often combines both of these is macro photography. Along with a wide aperture, a close up composition with a macro lens will often have a tiny depth of field measured in millimeters. Conversely, a wide angle lens set at f/16 can keep a sweeping landscape in focus with a usable depth of field measured in miles. If you’re using a camera with an optical viewfinder, you will not be able to see the effects of depth of field in real time unless you’re able to switch to a live view mode using your rear display. Electronic viewfinders, common on point and shoots and rangefinder style digital cameras, will show depth of field changes as you shoot.

Maximizing sharpness

Even the most expensive lenses aren’t perfect, and if your goal is maximizing detail and sharpness, you’ll need to find the sweet spot in your lens’ aperture range. When you shoot ‘wide open’ on your lens’ lowest f-stop, you’ll probably notice a certain softness known as aberration, even if you’re in perfect focus. At the opposite end of the aperture range at around f/16 and f/22, you’ll also run into less than ideal optics through a similar effect called diffraction. Aberration and diffraction decrease and effectively disappear through your lens’ mid range aperture settings. If you want to optimize for sharpness and clarity, try keeping your f-stop between f/5.6 and f/8 – you may also want to consider keeping your subject in a more central position, as the edges of your frame are the most prone to optical distortions.

When to use a wide aperture

From a technical perspective, it makes sense to use wide apertures in the f/1.4 to f/3.5 range in low light conditions. Indoor lighting, concerts, and twilight are all scenarios where lighting can be limited. By opening up your aperture, you can hopefully use a shutter speed fast enough to keep your shot stable and sharp. Additionally, you may also want to boost your camera’s ISO to increase the overall exposure, but this will often come at the expense of a ‘noisy’ or grainy look. If your camera or lens has an image stabilization mode, you can use it in combination with a wide aperture and slower shutter speed to maximize your ability to shoot low light.

Creatively, wide aperture shots leverage shallow depth of field as described earlier. The blurred, round orb effect that appears in the background is known as bokeh, and can vary quite widely in appearance from lens to lens. However, no matter what lens you use, the wider your aperture, the larger and more blurry your bokeh becomes. Placing a subject against this blurred background will intuitively draw viewers into them, as the sharp details appear in such stark contrast to the softness that surrounds them. Portraiture is a common use-case for creative wide aperture shooting, but you can expand the same principle into other compositions and genres. If you find yourself composing a shot and you’re particularly drawn to a smaller detail or area of the frame, you can use a wide aperture to emphasize it and make it stand out against a ‘busy’ background.

When to use a narrow aperture

Because of the smaller opening inside your lens, narrower apertures of about f/8 and higher require lots of light to create a good exposure. Unless you’re making use of a tripod or flash, you’ll almost always use the high end of your aperture range in outdoor, natural light. When using aperture priority mode with a higher f-stop, keep an eye on your shutter speed to make sure it’s not so slow (1/60 or longer) that it causes motion blur. If it does, try opening up your aperture to a lower f-stop number for a more well balanced exposure.

The expanded depth of field created by narrower apertures opens up unique compositional opportunities. Rather than focusing on one area or detail within your frame, you can expand into the entirety of your frame, creating complexly layered compositions with multiple points of interest. Additionally, because the area of focus is so wide, you can often set it in advance and not have to worry too much about an out of focus image – this can be hugely helpful when tackling more spontaneous styles of shooting like street photography, as you can instantaneously click the shutter while keeping your autofocus off.

To make the most of a deep depth of field, it is helpful to think about your composition in terms of layers – foreground, middleground, and background. The classic ‘rule of thirds’ can help guide your composition in the right direction using these same principles. Try placing a significant subject or detail in each layer or area of your composition. By creating a tension, contrast, or flow between them, you can hold your viewers attention and force them to think about the visual relationships built within your frame. Landscapes are a great genre to experiment with in this regard, but don’t shy away from incorporating it into your own personal style – practice makes perfect.

Hitting all the notes

Aperture is a fundamental aspect of photography, and lies at the center of both the technical and creative sides of the medium. Being able to work your full range of f-stops is a lot like mastering the full range of notes and scales on a musical instrument. They can be manipulated, placed in contrast to one another, or work together to create compositions that are greater than the simple sum of their parts. Put your creativity to work – we’d love to see what you make along the way.

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