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How to Master The Exposure Triangle


Jo Plumridge

This article is an extract from Issue 9 of Photography Masterclass Magazine
Black and white drawing of camera
PixBox77/ Shutterstock.com
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The world of photography has undergone huge changes in the last few decades. Digital technology is now at the forefront of most photographers’ lives, but the core of photography really hasn’t changed.

The most important step to becoming a skilled photographer still remains the ability to understand and use the exposure triangle. The exposure triangle refers to ISO, shutter speed and aperture.

I call these three functions the exposure ‘triangle’ because of the way they work together. If you change one function, it affects the next, which affects the next and so on; thus creating an eternal triangle.

If you understand these three functions, you’ll always be able to get correctly exposed images, which is, of course, the main point of photography. In this guide, we’ll look at each one separately as well as telling you how to use them all together.

The 3 Elements Of The Exposure Triangle You Need To Understand To Become A Better Photographer

Diagram showing different ISO values


ISO stands for International Standards Organisation and is known as ASA in America (American Standards Organisation).

Back in the days of film, rolls came with ISOs ranging from 25 up to 3200. The number referred to how sensitive the film was to light and the lower the number; the more light was needed to achieve the correct exposure. The trouble with a roll of film, of course, was that you were stuck with the same ISO for the number of exposures on the roll.

Nowadays, digital cameras come with a dedicated ISO button (or at least a way to access it in the menu). This means that you can alter your ISO from shot to shot. And modern cameras also come with a much larger ISO range than found in film. Although most can only start from a base of 50 or 100, they go up to 300,000 and above.

However, the catch with ISO is that the higher the ISO you use, the more ‘noise’ you get in your image. Noise is the term for digital grain, which can cause image deterioration and slight softness. Unfortunately, noise is not quite as flattering as old-style film grain!

As technology improves, noise is becoming less of an issue and you’ll find that you can use high ISOs without any discernible loss of quality. But do note that, whilst ISO is probably the easiest of the three facets of the exposure triangle to understand, it’s generally the last of them that you should alter.

Start with your ISO on its lowest setting (usually 100) and change it once you’ve exhausted the possibilities with your shutter speed and aperture.

Black and white drawing of a camera film box


Shutter speeds range from 1/8000th of a second (or 1/4000th of a second on mid to lower-end cameras) down to a ‘Bulb’ setting, which allows you to leave the shutter open for as long as you wish. Full seconds are denoted on the camera display with a double quote mark (e.g. 2”).

To shoot handheld and maintain absolute sharpness, you’ll need a shutter speed of 1/60th of a second or faster (unless you have very steady hands, in which case you might get away with 1/30th or even 1/15th).

Do remember though if you’re using a heavy telephoto lens it’s a good rule of thumb to shoot a shutter speed faster than the focal length of your lens (e.g. shoot at a shutter speed faster than 1/200th of a second for a 200mm lens).

The faster your shutter speed, the less time the shutter in your camera is open for as less light is let into your camera.

So, why do we have all these different shutter speeds?

Well, fast shutter speeds allow you to freeze action, so are useful for shooting things such as sports or wildlife. Long shutter speeds are used for a variety of situations. Nighttime photography, low light landscape or still life work and for giving water a misty, ethereal feel are examples of this.

Obviously, if you’re shooting with long exposures you will need to use either a tripod, monopod or conveniently placed wall or bench! Also, bear in mind that if you’re shooting without a tripod outside on a dull day, you are likely to need to use a shutter speed of 1/60th of a second or faster to get as much light into the image as possible, whilst still being able to handhold.

Diagram of different shutter speeds demonstrating how motion blur increases with slow shutter speeds
Shutter Speed Chart Alhovik/Shutterstock.com


Of the three parts of the exposure triangle, aperture is probably the hardest to understand. But it’s also usually the setting you will go to first out of the three!

The reason aperture is more complex is because it controls two separate things – both the amount of light coming through the lens’ iris and the depth of field of the image. Let’s start by looking at depth of field.

Depth of Field

Depth of field is, in my opinion, the single thing that turns an amateur ‘snapper’ into a proper photographer.

Understanding and using it properly is crucial to getting great images and, once you get the hang of it, you’ll see an immediate improvement to your work.

Put simply, depth of field is a range of distances around your subject (known as the focal plane) that are in acceptable sharpness. There’s no abrupt change from sharp to unsharp – depth of field occurs as a gradual transition.

So, how do we tell whether our shot is going to have a small depth of field (very little behind the subject sharp), or a large depth of field (all of the photograph is sharp)?

Diagram showing different f-stop depth of field values and different levels of background blur for each

Depth of field is controlled by f-stops. A small f-stop number, such as f2, will give a small depth of field, whereas as a large f-stop number, such as f22, will give a large depth of field.

Applications for Depth of Field

A large depth of field is used for photographing things such as landscapes, where you want the whole image to be sharp.

Really small depths of field are generally used for jewellery and macro work. Portraits also benefit from smaller depths of field, such as f4 or f5.6 for head and shoulders shots. This allows you to keep your subject sharp, whilst throwing the background out of focus thus allowing your subject to really stand out and ‘pop’.

When you see really eye-catching portraits where the subject is sharp and the background is beautifully blurry, the way this is achieved is by using a small depth of field (small f stop number).

It’s also worth noting the ‘effect’ of focal length on depth of field. Focal length doesn’t actually influence depth of field although it can sometimes look as if it does.

A telephoto lens may appear to create a much shallower depth of field, but this is because they are generally used to magnify a subject. So, if your subject occupies the same fraction of the image with a telephoto and wide-angle lens, the total depth of field will be virtually constant with focal length.

Obviously you’d need to get much closer with a wide-angle lens to achieve the same effect as with a telephoto. However, there are some cases where this doesn’t hold true. For focal distances resulting in high magnification, wide-angle lenses can give a greater depth of field than telephoto lenses!

It’s a somewhat complicated concept and shows a limitation in the concept of depth of field. Whilst the total depth of field is taken into consideration, its distribution around the focal plane isn’t – and this may be a factor in overall sharpness perception.

The best way to think of it is thus. Wide-angle lenses give a gradually fading depth of field behind the focal point, rather than in front. Whereas telephoto lenses enlarge the background with a narrower angle of view. This increases the ‘look’ of a shallow depth of field, making the background look even blurrier.

Controlling the Amount of Light

The other function of apertures is to control the amount of light coming through your lens’ iris. This is where it gets slightly more complicated.

A large aperture is represented by a f-stop small number (e.g. f/2) and lets the most amount of light into your lens, with the iris being wide-open. A small aperture is represented by a large f-stop number (e.g. f/22) and lets less light into your lens, with the iris closed down and small. The phrase ‘opening up a stop’ refers to making the aperture larger and letting more light in, whereas ‘stopping down’ refers to making the aperture smaller and letting less light in.

So, when using your f-stops you need to balance out the depth of field you want with the amount of light being let into your camera.

Images of camera apertures. Top Left: Small Aperture / Large f-stop number (e.g. f/22) Bottom Right: Large Aperture / Small f-stop number (e.g f/2.8)
Top Left: Small Aperture / Large f-stop number (e.g. f/22)
Bottom Right: Large Aperture / Small f-stop number (e.g f/2.8)

How To Bring The Exposure Triangle Together To Create Beautifully Exposed Images

Once you’ve mastered the three elements of the exposure triangle, you need to bring them all together to get the correct overall exposure for each shot you take.

First, we’ll look at doing this when shooting in manual mode, and then we’ll look at some of the semi-automatic modes available on most DSLRs and mirrorless cameras.

Firstly when shooting in manual mode, how do you tell if your image will be correctly exposed? Just take a look at your camera’s exposure compensation line. This runs from either -3 or -2 up to +3 or +2.

An image is correctly exposed when the needle is on 0. To see if your image is correctly exposed, half-press your shutter button. The white needle will flash below your exposure compensation line to give you a reading. If the needle is flashing at a minus number, it means your shot will be underexposed, and if it’s flashing at a plus number, your shot will be overexposed.

Photography always boils down to light and its availability. Whether you’re using natural or artificial light, your exposure is all about controlling said light to produce the image you want. But, whilst you should always be thinking about light, there are other factors to consider when choosing what settings to use.

In many photographic situations, your depth of field is going to be the first thing you consider. As previously mentioned, for example, if you’re shooting a landscape you will need a large depth of field of around f/22. This means that you’ll be using a small aperture that won’t be letting much light into the camera through the iris of your lens.

Conversely, if you’re shooting a portrait you’ll be using a small depth of field of around f4/f5.6, which means that you’ll be using a large aperture that will be letting a lot of light into your lens.

Exposure compensation camera setting

So, once you’ve decided what depth of field you need and set your aperture accordingly, you’ll need to adjust the other settings of your exposure triangle to compensate.

If you’re shooting a portrait with a small depth of field and large aperture, you’ll want to use a low ISO to keep any noise out of your image (noise is particularly unattractive in portraits). But, as you’ll be letting a lot of light in through your lens you will be able to use a faster shutter speed so that your exposure is correct.

When shooting a landscape you won’t be letting much light in through your lens due to the large depth of field and small aperture. This means you have to compensate with either your shutter speed or ISO. Ideally, if you’re using a tripod you will use a longer shutter speed to allow enough light into your shot.

However, if you’re using your camera handheld you will have to up your ISO instead, as you will be tied into a shutter speed of at least 1/60th of a second to avoid camera shake.

Sometimes, of course, your shutter speed will be of more importance than your depth of field (although depth of field always needs to be considered).
If you want to use a long exposure for situations such as night time photography or to give water an ethereal misty look, then this ties in well with using a large depth of field and a small aperture. The small aperture will allow you to use long exposures without the risk of overexposure.

If you are photographing action such as sports or wildlife, your first thought will obviously be to choose a fast shutter speed. This is so that you can freeze the action. This will mean that the shutter in your camera is open for far less time, thus not allowing much light into your camera.

This leaves you with several options to get more light into your camera. You can use a large aperture, which will give you a smaller depth of field and help isolate your subject from the background. This can also help to give a sense of movement to your shot.

If you want a larger depth of field to get more of the action sharp, you can either shoot on a day when there is a lot of natural light, or you can up the ISO if you’re working in dull conditions.

Remember – a very fast shutter speed will freeze everything so if you want to keep a little bit of movement in your shot go for a slightly slower shutter speed of around 1/250th – 1/500th of a second combined with tracking focus.

Our Quick Start Checklist For Mastering the Exposure Triangle:

Here’s a quick checklist to help you remember things:

✔️ ISO

The lower your ISO, the more light you’ll need to get your shot. Start with your base ISO (usually 100) and raise your ISO after you’ve exhausted the possibilities with your shutter speed and aperture.

✔️ Shutter Speed

Use fast shutter speeds to freeze action, such as sports and wildlife.

Use slow shutter speeds for night time photography, lowlight landscapes or to give water a misty ethereal look.

Shoot at 1/60th of a second or faster if you’re using your camera handheld to avoid camera shake.

✔️ Aperture

Use a small depth of field (which is a large aperture / small f-stop number) for small still life and portraiture where you’d like a sharp subject and a beautifully blurred background.

Use a large depth of field (which is a small aperture / large f-stop number) for landscapes where you’d like most of the image in focus.

Aperture, Shutter Speed, ISO, & Light Explained – Understanding Exposure & Camera Settings

Exposure Triangle – In Conclusion

Mastering the exposure triangle is a crucial step in becoming a better photographer. It can be a little complicated to get your head around, but with a bit of practice you’ll get there, and you’ll see the quality of your photos improve dramatically as a result.

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