The sacred trinity of photography: What you need to know about aperture, shutter speed, and ISO

A solid understanding of aperture, shutter speed, and ISO differentiates the seasoned photographer from the casual photographer.

This trio of camera functions is responsible for image exposure (the level of light and dark tones in your photo), allows you to manipulate other artistic aspects of your photograph, and consequently plays a large role in the overall look of your image.

The first step to mastering aperture, shutter speed, and ISO and becoming a better photographer, is to switch from taking photos in Automatic mode (in which the camera takes care of all the settings) to shooting in full Manual mode. Setting your own exposure does take longer in Manual, however the mastery you’ll gain from the process is invaluable.

To get you started, let’s look at the three exposure settings in detail, how each of these settings can influence artistic image properties, and how they all work together in what we call the ‘exposure triangle’.

The Exposure Triangle

The Exposure Triangle

At a glance: the three sides of the exposure triangle

Aperture is the opening in the lens that allows light to reach the sensor.

Shutter speed is the speed with which the camera’s shutter opens and closes.

ISO is how sensitive the sensor is to light.

Aperture, shutter speed, and ISO are collectively referred to as the exposure triangle because in order to achieve optimal exposure, all three must remain well-balanced. When the exposure triangle is well-balanced, yielding optimal image exposure, the combination of settings is represented by an exposure value (EV) of 0.

The Exposure Meter

The exposure meter (also called the light meter) showing ‘optimal’ exposure with an EV of 0.

When you first start shooting in Manual mode, you’ll notice that as you adjust each setting, the exposure value shifts, telling you that your image is going to be either underexposed (<0), overexposed (>0) or well-exposed (=0).

Yet while different levels of aperture, shutter speed, and ISO can give one and the same EV value, the ‘look’ of the images you take will differ slightly.

Why? Because while these tools allow us to control the brightness of the image, they also give the photographer creative control over how the final image looks. Let’s take a closer look at each of these settings.

Same scene, same exposure value (EV = 0); different combination of aperture, shutter speed and ISO. Notice the slight differences between both images.

01. Aperture

Aperture is most simply described as the opening within your camera’s lens controlling the amount of light that enters the camera. When the aperture is wide open, lots of light can enter the lens, and when it’s small very little light can enter.

The size of the aperture is measured in focal stops, or f-stops, and is based on the diameter of the hole through which light enters the camera.

Aperture Photography

When the aperture is small and more closed, it’s represented by a high f-stop number (e.g. f/16) and results in a darker image. Conversely, when the aperture is large, lots of light can enter the camera resulting in a brighter image. The wider the aperture the lower the f-stop number (e.g. f/1.4).

In addition to controlling image brightness, aperture is the tool used to determine the depth of field of our photo.

What is Depth of Field?

Depth of field (or DOF) is the amount of area that is in focus around your subject.

Depth of field

Small (or shallow) DOF blurs the area around the subject. Large DOF keeps more of the area behind the subject in focus.


Photo by Joe Gardner

To create an image in which the subject is in sharp focus and the area around it is blurred, you’ll need to shoot with a wide aperture (a low f-stop number). This shallow DOF works particularly well in portrait, wildlife and sports photography, where you want the subject to stand out against the background.


Photo by Alex Blăjan

Shooting with a very wide aperture also allows you to achieve a ‘bokeh’ effect, a popular aesthetic quality of the blur that occurs for parts of the scene that lie outside the depth of field.


Photo by Liam Pozz

To bring more of the area around the subject into focus, you’ll need to decrease the size of the aperture (change your setting to a higher f-stop number) which will broaden the DOF. This large DOF is great when photographing landscapes or situations in which the background matters.


Photo by Garrett Parker

Hint: Try setting your camera to Aperture Priority mode (usually an A or Av, depending on the camera) which allows you to control the aperture while the camera automatically configures the other two.

02. Shutter Speed

This refers to the length of time the shutter is lifted to expose the sensor to light. Measured in fractions of a second (e.g. 1/125), shutter speed allows you to control the definition quality of your image much the same way aperture does, but is best observed when there’s something moving in the scene.

Shutter Speed

Fast shutter speeds allow us to freeze motion whereas slower shutter speeds allow us to blur motion. As with aperture, we have to adjust the other two exposure settings to keep the triangle balanced.


Photo by Mike Lewis

Slow shutter speed exposes the sensor to your scene for a longer period of time and as a result any moving object will appear to be in motion — or blurred — in your image. This isn’t necessarily a bad thing. On the contrary, many photographers use a slower shutter speed to capture situations that involve movement such as a speeding train, the gradual shifting of the stars in the night sky, or flowing water.


Photo by Benjamin Voros

Inversely, fast shutter speed means the sensor is only exposed to the image and light for a very short amount of time, capturing the scene for a split second and therefore freezing a movement in time.

Avoiding Unwanted Blur

One thing to consider when adjusting the shutter speed settings is that below a certain speed a tripod or stabilizer may be necessary to maintain a sharp image. This is because for handheld shots, the photographer’s movements (no matter how minimal) can cause the image to blur.

The minimum setting for taking sharp handheld photos varies depending on the focal length of your lens (unless your lens has built in stabilization): the larger the focal length, the greater the risk of camera-shake. The general guideline is that if you’re shooting with a 200mm focal lens, choose a shutter speed faster than 1/200 of a second. Generally, the slowest shutter speed for any lens is around 1/60 of a second.

Hint: Once again, cameras provide a partially automated mode — in this case Shutter Priority (S or Tv) — which allows you to adjust shutter speed alone, while it calculates the other two settings for you.

03. ISO

The third and final ‘side’ of the exposure triangle is ISO, which can most simply be described as the element that affects the sensitivity of the sensor to light.

ISO Photography

Increasing ISO increases the brightness/exposure of a photo, as you can see from the example above (EV -2, 0 and +2 respectively).


Photo by Dave Lastovskiy

If you’re shooting in a very low-light situation, a higher ISO will ensure that the sensor is able to absorb as much of the available light as possible and allows you to capture the ambience of a setting without having to use flash.


Photo by Kalen Emsley

When photographing a scene with lots of light, a low ISO of around 100 or 200 should be sufficient for the sensor to absorb the light it needs.


This photo was taken in a very dark setting with an ISO of 6400.

One thing to be aware of when using a high ISO to boost the exposure of your photo is that this heightened sensitivity to light can result in a noisy image. This ‘noise’ — a speckled, grainy appearance — can reduce the quality of the photo, so it’s recommended that you keep your ISO as low as possible for a crisper image.

So now you’ve got an idea of the elements that make up the exposure triangle, let’s delve a little deeper into the all-important concept of exposure in photography.

Managing Exposure

Photography is the art of light and how to manipulate this light to get the desired image. As we’ve just learned, the way we do this is through our exposure settings, which determine how much light is allowed into the camera’s sensor (or film) and ultimately the brightness of our image.

If we allow too much light to enter the camera, the photo will look washed out and overly bright, with predominantly white areas (overexposed). Not enough light results in an image that is too dark and lacking in detail (underexposed). The ‘correct’ level of exposure is one that balances the light and dark areas and makes the image look as natural as possible (typically represented by an exposure value or EV of 0).

Photo by Robert Bye

When shooting in Auto mode, our cameras are typically quite good at deciding the best exposure for any scenario. However, when the amount of available light is at the extreme ends of the spectrum (a snowfield, a windowless room, sun rays shining directly into the lens) the camera may miscalculate and produce an image that's not properly exposed. Hence the importance of knowing how to take control of the exposure for ourselves.

There are a few additional tools you can find in most digital cameras that help with exposure.

01. Exposure Meter (a.k.a. Light Meter)

As mentioned earlier, the exposure meter is a useful tool when shooting in Manual mode, to help you gauge your exposure value (EV) and maintain a well-balanced exposure triangle. Use by pointing the lens at the scene you’re shooting and observing how the exposure value changes as you adjust each setting. An EV of 0 suggests that the image is properly exposed.

02. Exposure Compensation

Exposure Compensation

This tool is a quick and easy way to alter any exposure when you are shooting in Manual, Aperture Priority or Shutter Speed Priority modes when you want an image that is intentionally lighter or darker than the default EV of 0. This is done by adjusting the marker on the scale – higher to make the subject appear lighter and lower to make the subject appear darker.

03. Histogram


The histogram is a visual tool that allows us to fine-tune a photo’s exposure. The way it works is by showing an image’s luminance on the horizontal axis of the graph, with pure black on the left edge and pure white on the right edge. The vertical axis shows the quantity of pixels that fall within this range. An image is ‘correctly’ exposed when the majority of the graph falls in the middle of the graph.

Correct Exposure

It’s important to note that ‘correct’ exposure really depends on the goal of the photo and can vary greatly. If your artistic vision is an image that is underexposed or overexposed, and you deliberately create that through adjusting your camera settings, then you have achieved the ‘correct’ exposure.


Photo by Sergi Bozhko

Overexposing your images can create a light, ethereal, impressionistic visual effect.

Selecting your exposure based on the dark parts of your image can create a glowing, overexposed photo in which the light background fades to white and the subject appears softened.


Photo by Kari Shea


Photo by Rowan Neal


Photo by Gilles Lambert

On the flipside, if you’re trying to create a dark, shadowy or moody image, try adjusting your settings to allow less light to reach the sensor and underexpose the photo. Dark or black backgrounds can add drama to an image.

Over to you!

Equipped with a greater understanding of how each of your camera’s exposure settings work, the best thing you can do now is pick up your camera and start practicing taking photos in full Manual mode.

Experiment with achieving an EV of 0 using different combinations of aperture, shutter speed, and ISO, and play around with over- and underexposing your images. By adjusting each of the three components you’ll intuitively become aware of what’s required to get the exposure right for your desired image and how they can be used to artistically enhance your photo.

Happy photographing!

A couple of things to try with your exposure settings…

01. Play around with depth of field

Photo by Kira auf der Heide

Set your camera to the widest aperture available (the lower the f-stop number, the wider the aperture). As you close the aperture, notice how the depth of field gets larger, bringing more of the scene into focus. Play around with your camera’s point of focus with the various depths of field to see what artistic effects your lens is capable of.

02. Freez or blur movement


Photo by Pana Vasquez

Experiment with shutter speed by photographing moving subjects (a fountain or flowing water is a great subject to practise with), freezing them in action or allowing them to blur and in doing so accentuating the motion. Try shooting a night scene with a really slow shutter speed and using a sturdy tripod – you can get some fantastic motion blur results!


Photo by Orlova Maria

Change your ISO for a range of situations with high and low light, to see to what degree it affects the brightness of your photo and if you notice any change in crispness of the image.

The more familiar you become with aperture, shutter speed and ISO, the more competent you’ll become at deciding for any given scene exactly which settings will get the very best image possible.

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