What is Aperture? Introduction Lesson

Aperture in photography is a diaphragm in lenses that controls the amount of light that can enter the camera. This function works in a similar way to how the iris in the human eye opens and closes to let more or less light in. Aperture affects the depth of field also. Lenses are measured by their focal length and the widest aperture. The set of numbers used to measure the aperture setting are called f numbers or f stops. These f stop numbers seem to be a rather random collection of numbers used to measure the aperture opening size. This is because the f-stop is a ratio of the lens’s focal length to the size of the aperture opening.

In our lesson on understanding the exposure triangle, we talked about the importance of light in photography. We also looked at controlling how much light reaches the digital image sensor in your camera to produce a well-exposed image. You learned how the ISO, along with the aperture setting and the shutter speed, control how much light enters the camera to make your image. These three pillars, the exposure triangle, work together to control the lightness or darkness of a photograph. Today we’re going to talk specifically about aperture.

Table of Contents

• Introduction to Aperture
  • Understanding Aperture in Photography
  • The Basics of Aperture
  • How Aperture Affects Depth of Field?
  • How Aperture Affects Shutter Speed?
• How to Change Aperture with your Camera?
  • Auto Mode
  • Aperture Priority Mode
  • Manual Mode
• The Best Lens for the Best Aperture?
• Aperture for Landscape Photography
  • The Aperture Sweet Spot
  • Narrow Aperture – High F Number
• Aperture for Portrait Photography
  • Control your background
  • Ensure the face is sharp
• Creative Techniques that Use Aperture

Introduction to Aperture

Aperture definition: It is the opening in the lens through which light passes to the camera and is measured in f-stops (or stops), which usually ranges from f/1.2 to f/32. Inside the camera lens is a mechanical iris diaphragm that controls the amount of light transmitted to the imaging sensor in the camera. The diaphragm stops the passage of light, except for the light that passes through the hole (or the aperture). It’s a lot like the shades on a window control the light.

Charles Bryant created a great video clip that will teach you the basic principles of aperture.

Understanding Aperture in Photography

We love this quirky 36-second video from Canon Australia that briefly describes aperture and how it affects depth of field.

Aperture plays two important roles in photography. First, it controls the amount of light that passes through the lens, to get a properly exposed image. When you change the f-stop value, you change the opening of the iris. The lower the f-stop, the larger the size of the opening (just the opposite of what you might expect).

Second, it helps control the depth of field (which is the range in an image that is in acceptably sharp focus). Another way to explain the depth of field is the area of sharpness in front of and behind the subject you’re focused on.

Changing apertures from one f-stop to the next (up or down) doubles or cuts in half the amount of light passing through the lens. A smaller f-stop number like f/2.8 means a larger opening of the iris when you change the aperture from f/2.8 to f/4, it’s called stopping down.

Lenses have a range of apertures. All lenses do not have every aperture available. When we say a lens is a 2.8 lens, that means the lowest aperture available is f/2.8. In the diagram above you can see f-stops of; f/1.4, f/2, f/2.8,f/ 4, f/5.6,f/ 8, f/11, f/16, f/22, and f/32.

Changing the aperture is usually a setting inside your camera. On older lenses, each f-stop number is etched into the aperture ring and is changed by turning the ring.

The Basics of Aperture

Here’s an entertaining 6-minute video on The Basics of Aperture by Larry Becker at B&H Photo. It goes into a little more detail on the mechanics of the function of the aperture in photography.

How Aperture Affects Depth of Field?

A wide-open aperture results in a shallow depth of field, whereas a narrower aperture results in a deeper depth of field. If you want to know why this is, see our lesson on the physics of depth of field. If you’re interested in knowing what the “f” is about in all the aperture settings, see our lesson on aperture f-number.

How Aperture Affects Shutter Speed?

In a lot of instances, your ISO is going to be set to a fixed point. In fact, if you’re photographing with film, this is certainly the case. That means the relationship between aperture and shutter speed is a bit like balancing some scales. The larger the size of the aperture hole is, the faster the shutter speed needs to be to maintain a good exposure. The narrower the opening (a small aperture), the slower the shutter speed. This means you can use something like aperture priority mode to also adjust the shutter speed. You do so indirectly by changing the aperture, which will also affect the shutter speed.

How to Change Aperture with your Camera?

Now you know more about what aperture is, it’s time to look at how you can change it on your camera. This is easier on some cameras than on others. If you’re using a smartphone, your aperture may be fixed, and iPhone for instance has a fixed aperture of f/1.8. However, using a DSLR or mirrorless camera will give you control over the aperture. Take a look at different ways you can manage the f-numbers through your camera settings.

Auto Mode

In fully auto mode, you have no control over the exposure triangle. Your camera will choose the aperture for you, along with an ISO and shutter speed. It will manage the amount of light and give you a balanced exposure. Some cameras have automatic modes for portrait, macro, and landscape photography. The aperture will be set according to the mode. In portrait mode, a wide aperture would be used. Whereas for landscape mode, the camera is likely to choose apertures like f/11 or f/16 (a narrow/small aperture.) These modes will vary between Nikon, Canon, Sony, and other camera brands.

Aperture Priority Mode

In this mode, your camera is essentially semi-automatic. You choose the aperture, while your camera chooses the shutter speed and sometimes the ISO as well. You control the f/stop, the aperture size, and the camera controls the exposure with the shutter speed. This is the mode you’ll want if the lens aperture setting will affect your photo in a specific way. The camera aperture you choose could be used to blur out the background. Or you may wish to have a greater depth of field for a landscape photo, so choose a narrow/small aperture. One advantage of aperture priority mode is speed. You only have one setting to change, which can be done quickly, making it much easier to get shots.

Manual Mode

In manual mode, you have total control of all your exposure triangle settings, allowing you to get the right amount of light for your image. In this mode, you have control of the three controls of the exposure triangle. These settings are ISO, shutter speed, and of course, the aperture. These in turn affect the exposure value of your photo.

The advantage of this is you’ll be able to set your camera up for the exact type of exposure you want. The drawback is, before you’re used to it, it takes a little longer to adjust all three settings to produce the level of brightness you want in the photo. Learning to use manual mode is not so difficult and gives you more creative freedom as a photographer.

Are you interested in learning to control your aperture in photography, along with the shutter speed, ISO, and other aspects? Check out our 365 Photography Course.

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The Best Lens for the Best Aperture?

Now you know what aperture is, it’s time to talk about equipment. There are many different types of camera lenses, and the main choice is between a zoom lens and a prime lens. The distinction is important because of what they’ll mean for your aperture.

Prime Lenses

The prime lens has a fixed focal length, and these are known for their wider aperture. With the fixed focal length, a larger piece of glass can be used, and your lens will still be relatively lightweight. Let’s look at some of the common prime lenses you could opt for. The maximum aperture for a primes lens can be an aperture of f/0.95, but these lenses are rare and very expensive.

• 35mm – A wide angle lens for a full frame, and a mid-range focal length on a crop sensor. Most manufacturers offer a 35mm f/1.4 or f/1.8 lens, which is a good option.
• 50mm – This lens is a favorite among many photographers. The most affordable has an aperture of f/1.8 but there are variants that have apertures like f/1.4, f/1.2 or even lower.
• 85mm – A great portrait lens typically with a nice wide aperture of f/1.4 which you can blur the background with.
• 135mm – On the telephoto end of the scale, but still a great street or portrait lens. Lenses at this focal length can have a wide/large aperture of f/2.

Zoom Lenses

The zoom lens offers you variable focal lengths with the same lens. This is great, but there is a downside. The widest lens aperture for this type of lens is narrower than you can get on a prime, so this is an area you’ll have to compromise on. At the cheaper end of this market segment, you’ll get zoom lenses with a maximum aperture of f/4-f/5.6. This type of lens is sometimes only useful during the daytime, with a high ISO, or in low light with a tripod. Are you willing to spend more money? If so, you can buy a zoom lens with a wide/large aperture of f/2.8 or in a limited number of cases, f/2. In fact, some photographers go with the f/2.8 trilogy of lenses, the 16-35mm, 28-70mm, and the 70-200mm lenses. These three lenses have a combined zoom range of 16mm to 200mm.

Aperture for Landscape Photography

The best aperture for landscape photography often comes down to the sweet spot of the lens you’re using for your photo. There will be times you will use a narrower, small aperture though, when you need a deeper depth of field.

The Aperture Sweet Spot

The sharpest focus your lens can achieve will be determined by your lenses’ sweet spot. What that sweet spot is will depend on your lens, though there is a simple way of working this out. Take your lenses maximum aperture, and your sweet spot will be 2-3 stops down from this. That means your f/2.8 lens will have its sweet spot between f/5.6 and f/8. A lens with a maximum f-number of f/4 will have the sharpest performance between f/8 and f/11. Why don’t smaller apertures offer sharpness since they offer greater depth of field? A process called lens diffraction starts to affect performance when you use narrower apertures. This does not affect the depth of field but results in distortion and lack of sharpness in images.

Narrow Aperture – High F Number

A narrower aperture usually means an aperture/f number like f/16 or higher. This means a deeper depth of field. Given what you’ve learned about the lens sweet spot, why use these apertures? Well, there can be many scenarios for a landscape image.

• Foreground element. – Landscape photos that have foreground elements close to the lens, can benefit from the deep depth of field a narrow aperture will offer.
• Long exposure. – There could be times when using higher f numbers aperture allows you to make a long exposure photo, especially if you don’t have a strong ND filter. You will also have a deep depth of field.
• The starburst effect. – This effect is produced by using a high f number, it can be great for street lights, or the sun, or some other small source of brightness.

Aperture for Portrait Photography

In portrait photography, aperture is also important. In this area of photography, it’s often desirable to use background blur to give the portrait image more impact. It also has an impact on the face, and it can lead to some undesirable focus issues.

Control your background

As a photographer is always good to control your background, this is especially true with portrait photographers. Aperture is not as much an issue in the studio, or if you’re photographing against a plain wall, where there is not perceived depth.

However, in outdoor locations where the background is layered, then using a shallow depth of field to control this is a popular option. To get the best results, make sure there is some distance between your model and the background. Then use a wide aperture to create a shallow depth of field. An aperture/f number of f/2.8 will often achieve this result. This does depend somewhat on the focal length and how far aware your point of focus is. You’ll have to take into account the brightness and the other exposure controls.

Ensure the face is sharp

It’s often tempting to use the widest f stop possible, especially one that blurs the background of the image producing bokeh. However, your subject is the model; you don’t want your shots to have a blurry face. You need more depth of field in your portrait images.

With portrait photos, the focus point is on the human eye. But what happens when you have a shallow depth of field produced by a wide aperture? The result is the eye of the subject is in focus, but the nose in the foreground and the ears in the background are out of focus. This is something you’ll usually want to avoid, so using an aperture/f number f/2.8 or narrower will give you better results.

Creative Techniques that Use Aperture

You can use a camera aperture for some photography techniques to produce a particular style of photography. Apertures in the mid-range will give the sharpest results. Effects such as bokeh are easier to achieve with the aperture range on the wider end. This is just one of many techniques you can try, so read on to discover more. With each technique, where you focus is relative to how effective the results are.

Starburst effect

This is a great technique for landscape photographers to use and will add interest to your photo. The effect is produced when you use a narrow camera aperture. Any f-number higher than f/11 will usually be enough. You’ll be somewhere photographing a great deal of brightness coming from a small source.

How is the starburst produced?

This effect is produced by the light escaping onto the image sensor through small gaps in the aperture blades. It’s only noticeable when the aperture is very narrow, and the aperture blades act to block out most of the light. Your point of focus will be in the light source or close to it. Another thing to note is that the lens you have will have a direct impact on the number of spikes for your sunburst.

• Even numbers of blades. – When you lens has an even number of aperture blades the number of spikes on your star will equal the number of blades in your lens. That means six blades will produce a six spike star.
• Uneven numbers of blades. – Those lenses that have an uneven number of aperture blades will produce a star that has double the number of spikes than there are blades in the lens. This means your seven aperture blade lens will produce a fourteen spike star.

Which subject will work?

To produce this effect, you’re looking for things that produce one point of light. The following are the two main options when practicing this technique.

• Street lights – At night time these are excellent an subject. They can form lines of star lights that run along the edge of a road in your cityscape image.
• The sun – A little trickier to get right, but it’s possible to produce the starburst effect with an f number of f/16 and narrower. The aim here is to block part of the sun so it appears as a point of light, and not a round disc. To achieve this use tree branches, clouds, or horizon lines to semi block the sun.

Blur the background

The use of depth of field to control the background of your image is one of the ways you can use aperture. In fact, this is one of the most common examples of how to use aperture. The technical name of this out-of-focus part of your photo is bokeh.

Now bokeh can be applied in different ways in your image. The following are examples of how to use bokeh in your images.

• Portraits – In this example the aim is to create a nice smooth background for your images. To do this use a wide/large aperture of perhaps f/2. Focus on the eyes. The image will now have more focus on the model, as your background is blurred. The closer your point of focus is, the more background blur you will see.
• Tell the story – You can use background blur to give your photograph more narrative, an aim for every photographer. To do this you’ll need to select an aperture that uses depth of field to blur the background, but perhaps not too much. To do this use an f number like f/4, or f/5.6. This will also depend in the focal length you’re using and how far you are from your subject. Then your aim is to allow your main subject to interact with the background, to give your photo that story.

Bokeh lights

Another example of aperture in photography is when it’s used to create bokeh light balls. This takes the idea of background blur and applies it to out-of-focus single points of light. Unlike the starburst effect, this time aperture is used to make these into bright orbs across your image. Also, opposite to the starburst effect, you will not focus on the lights. The lights will be as out of focus as possible.

To create this effect, point your camera towards single point light sources, use a wide f number of say f/1.8. Focus on your subject. Ensure the background lights are blurred behind your main subject. There are three typical ways you can get this effect in your image.

• Urban lights – Street lights that come on at night are an example of the type of lights you need to be aiming at.
• Fairy lights – Another example great for indoor photography. Illumination from these fairy lights can hit the image sensor as bokeh light balls.
• Sunlight – The final example you can use is sunlight, but this needs to be a specific kind of reflected sunlight. Look for sunlight shining on rippling water, or off individual leaves to get those points of light.

Creative bokeh

Bokeh light doesn’t just have to be spherical. In fact, you can get quite creative with the shapes produced. This is another way to use aperture in photography and provide a narrative element. In this example, you’ll need to get some black cards, scissors, and some tape to create a kind of lens filter.

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Master the Aperture Mode on your Digital SLR Camera

If you want to learn more about aperture, take a look at our article on adjusting aperture for extra information.