Exposure – Everything You Need to Know About it

Today, I will tell you everything you need to know about exposure. The three most important pillars of photography – aperture, shutter speed and ISO. Whether you are a beginner or one who has been into cameras for a while now, but have not been able to get a hang of manual mode yet, I am hoping this post will make it easier for you to comprehend all that.

What exactly is exposure? When you take a picture, you allow light to enter your camera, and that exposes your camera’s sensor to light. Now, if more light enters than is required, the photograph will become too bright, or overexposed. And if less light enters than is required, then the photograph will be too dark and underexposed. So, we have to make sure that the right amount of light enters the camera, and results in a correctly exposed photograph.

The Camera's Viewfinder - You can see Aperture, Shutter Speed and ISO at the bottom.
The Camera’s Viewfinder – You can see the Exposure Meter at the bottom.

The light meter you see in the viewfinder of your camera, helps you determine the correct exposure for every photo you want to take. If your meter is on the plus side, then that means that you are getting more light than required and your photograph will be overexposed and if on the negative side, that means that you are not getting as much light as is required and the photo will be underexposed. Now, how exactly is this measured? How we measure this light is in “stops”. So, if your meter is at +1, then that means that your photograph is overexposed by 1 stop. If it’s at -2, that means your photograph is under exposed by two stops. How much is a stop? Well, to put it simply, if you take a given amount of light and double it, you are moving up one stop. If you cut the light in half, you are going down one stop. So, if we go from 0 to +1, we are doubling the light. If we then go to +2, we now have 4 times the light we had at 0. Similarly, if we go from 0 to -1, we cut the amount of light in half. If we then go to -2, then we now have 1/4th the amount of light.

To settle the meter on this 0 point, or in other words, to achieve the correct exposure, the correct combination of aperture, shutter speed and ISO is required.

The Exposure Triangle - ISO, Shutter Speed, Aperture
The Exposure Triangle – ISO, Shutter Speed, Aperture

No matter how excellent of an approach a person has with the artistic stuff in photography, not having good knowledge about some of the essential mechanics will always prove to be a barrier for him. So, what exactly are these mechanics of the camera that we need to understand? Let’s take a look:



Aperture diaphragm blades – Diaphragm refers to the blades in the lens which control the diameter of the aperture.

Simply put, aperture is the size of the opening found inside each lens through which light enters into the camera and reaches the sensor.

The amount of light that reaches the sensor is dependent on the span of this opening which is our aperture. Hence, The wider the opening / aperture, the greater flood of light passes through to the sensor, whereas the smaller this opening is, it leaves lesser physical room for light to get in.

This way, with the aperture as wide as it can go, you get a lot of light reaching the sensor, so it naturally results in a brighter exposure and as you can now expect with a small aperture, the exposure is darker.

Aperture is also referred to as the “f-stop” and is denoted as “f/1.4”. You would notice that these numbers are inversely proportional to the size of the aperture. What that means is that the smaller number means a bigger opening. And a bigger number means a smaller opening. It can get a little confusing, but as you’ll practice more and more, you’ll get the hang of it.

Every f-stop opens double the amount of area of the aperture / hole than its previous f-stop, which means that each f-stop lets in twice as much light as the previous one.

Aperture’s Role in Depth of Field

Aperture plays an extremely important role in bringing dimension to any image. When you increase or decrease your aperture, it affects the depth of field of your photograph. What exactly is depth of field? Depth of Field (DOF) is that amount or area in your shot that will be in focus. Large depth of field means that most of your image will be in focus, while shallow depth of field means that only part of the image will be in focus and the rest will be blurred.

Relation of aperture with depth of field.

With a small aperture or a small opening, the rays of light that enter, are greatly collimated. Which is a term used for light when the rays are smoothly parallel to each other and are accurately aligned. This gives you a sharp focus. The more you constrict the diaphragm of the aperture, the more crisp focus you get.

Aperture F/13

Similarly, with a wider aperture, the light rays tend to disperse and spread all around, except, only the rays that go closely with the focus point are collimated. This results in the point of focus to be sharp only and the rest of the area around it will become blurry.

Aperture F/5.6

Hence, a wide aperture, that is: low f-number will give you a shallow depth of field. While a small aperture, that is: high f-number will give you a greater depth of field.

Relation With Other Two Pillars of Exposure

As the light coming in and reaching the sensor depends on the diameter of the aperture, and how blurry or focused you want your photograph to be depends on aperture also, varying it according to your need will require for you to balance the exposure by adjusting the shutter speed or ISO or ambient light or a combination of them.


Since when the aperture is very large and wide open, a lot of light reaches the sensor, this allows you to set a faster shutter speed. Which means you will be able to capture images faster. When your aperture is small, the amount of light will be lesser too, so this will require slower shutter speed.

While buying a lens, make sure to check what maximum aperture it offers. As the bigger the aperture opens, the better it is considering all the things we went through in this post.

A lens with a good small number / wider opening ability is known as a fast lens. Minimum aperture is not that important to worry about as almost all lenses come with at least f-16 as their minimum aperture and that is more than enough in most situations.

Shutter Speed:

Shutter is a screen that opens and closes over the sensor of the camera in a fraction of a second that allows the sensor to see the light. As the aperture controls the amount of light entering the camera, shutter speed controls how long the light enters the camera – the duration for which the shutter remains open.

Shutter speeds are usually expressed as: 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60 and so on. Each one in this series is approximately the half of its previous one and are a fraction of a second.

Just as aperture plays a part in the depth of field, shutter speed has some really useful qualities too, besides its main job. It has a strong connection with movement.

Displaying the “haze” with slower shutter speed.

If you want to show speed and motion in your moving subject, you use a slower shutter speed (for example, 1/10). It blurs the action and displays it as a haze, usually used in shooting waterfalls and car light trails. Shooting at slower shutter speeds require a strong stance and a steady hand as the shutter will be open for a longer time and will take in every single movement, even as slight as a jerk of a hand, and this usually can ruin any picture.

If you’re holding the camera in your hand while shooting at slow shutter speeds, camera shake is inevitable. So, upto what shutter speed is it that you can hold the camera in your hand? Some people say that 1/60th of a second is that point, but the correct value is actually 1/focal length of your lens. So, if you’re shooting on a wide angle lens at 10mm, you can take your shutter speed up to 1/10th of a second. If you’re shooting a telephoto lens of 200mm, it’d mean that you can’t hand hold the camera and go slower than 1/200th of a second as that might result in camera shake. Because at those focal lengths, even the camera shake is multiplied. If you go below this, the best option would be to use a tripod or take a firm support with something to steady your arms.

“Frozen” action

In order to freeze the motion as it is, a general rule of thumb is to keep the shutter speed as fast as you can. The higher the number, the faster the shutter speed and the faster the shutter speed the sharper the image, that is: no motion blur.

Shutter speed depends on a number of things such as the source of light and it’s direction, the amount of light, how fast your subject is moving, distance between the subject and your lens, the position and angle you went for, etc.

Slower shutter speeds allow the camera to take in more light, therefore it can help to brighten up an image if it is dark otherwise. Similarly, fast shutter speed will quickly roll over the sensor and close, as a result it won’t let the sensor register the light for long enough so if an image is too bright you can balance the exposure by shooting up your shutter speed.


Whenever you’re shooting, the first thing you check in your camera should be your ISO. In traditional (film) photography ISO was the indication of how sensitive a film was to light. It was measured in numbers (you’ve probably seen them on films – 100, 200, 400, 800 etc). The lower the number, the lower will be the sensitivity of the film.

A high ISO results in a brighter photo in comparison to a low ISO. However, each of the elements in the exposure triangle has a side-effect, that affects the photograph in another way as well. When you increase the ISO, you end up getting small grain or noise, on your photographs. So, the higher the ISO value, the more noise you would have in your photographs. Here, we see two photographs shot on different ISOs and you can see that the one with 1600 ISO has a lot of noise on it.

Left: ISO 100 and Right: ISO 1600 – Photo by © HuttyMcphoo

As every camera is different, it is best to take a few test shots with your camera to see in what conditions and at what levels your ISO begins to produce these grains. The point at which this noise comes in the photo will be different for every camera, and that’s also one of the important considerations before buying a camera.

Things to determine what your ISO should be:

Light: How much light is available to you from your surroundings. If you have a lot of light available to you, you can make do with a fast shutter speed and an open aperture, and hence would not be needing to increase the ISO in order to get the correct exposure. But on the contrary, if there’s low-light, then you would be needing to compensate for it by increasing the ISO, as your aperture and shutter speed might reach their limits and you would still have an underexposed image.

Grain: Many a people like to get a vintage old-school look, which has grains on their photographs. So if you would like for grain to appear on your photograph, a higher ISO will help you achieve a grainy outcome, while with a low ISO you get a smooth even image.

Tripod: If you have a tripod handy, you wouldn’t need to increase the ISO as you can always balance the light with a slower shutter speed. As slower shutter speeds mean that there is a chance of camera-shake, it is vital that there be a tripod in those situations so that the camera is placed on a steady surface.

Moving Subject: If you have a moving subject, then even a tripod would not be able to stop the motion blur. Because while the camera might have a steady grip, the moving subject will appear to have a motion blur. In order to avoid that, I would need to bump up my ISO, so I can get a faster shutter speed.


Now that we have seen ISO, aperture and shutter speed individually; let’s take a look at how they are related to each other.

As we understood, the primary function of all these settings is to control the amount of light the picture gets. Or in other words, it controls the exposure. Changing any of these settings by one stop would result in our exposure moving one stop. So, now let’s take a look at a situation. Let’s say that you are getting the correct exposure (exposure meter at 0) at f2.8 and 1/500th of a second. Now, f2.8 means that the depth of field would be shallow and 1/500th of a second means that there will not be any motion blur. Now, let’s say that the picture you want to take requires that the depth of field not be shallow, but more things be in focus. Can I close down my aperture? Sure I can. So, let’s say, I close down my aperture one stop, taking it from f2.8 to f4. While that will affect the depth of field, it will also affect my exposure, making it underexposed by one stop. The change in aperture is taking my exposure meter to minus 1. Now, how can I get the correct exposure without altering the aperture? By changing the shutter speed to 1/250th. If my aperture caused the meter to go down one stop, I can use my shutter speed to bring my meter up by one stop. So, you will get the exact same exposure in both these settings.

Reciprocals - You can achieve the same exposure at different settings
Reciprocals – You can achieve the same exposure at different settings

The same exposure actually can be achieved on various different settings. If you close down the aperture by one more stop bringing it to f5.6, you’ll have to slow your shutter speed to 1/125th to get the same exposure. Similarly, if aperture goes to f/8, shutter speed will have to go to 1/60th of a second in order to get the same exposure.

This is dictated particularly by the result that you are trying to achieve. If you are trying to achieve a shallow depth of field, then you will first decide on your aperture that will help you achieve that and then set a shutter speed that brings the meter down to 0. If you are trying to get motion blur, then you will have to set your shutter speed first at a value which allows you to get motion blur and then set your aperture to a value that brings the meter down to 0.

This can sound confusing in the beginning, but you have to keep practicing it in order to get the hang of it.

If you are feeling confused, then Canon has an amazing tool to help you practice it. Just go to this link: Canon Explains Exposure and play with this tool until you get the hang of how exposure works and how the three elements in the exposure triangle are related to each other.

This is the very foundation of photography and if you are able to master this, then you will be able to take your photography to new heights.