Every image begins with light. When you take a picture with your camera, you’re capturing light particles on a digital sensor to paint the image.
Exposure is the amount of light that you let into your camera when you press the shutter button. You could have the greatest compositional ideas, but without good use of exposure, your ideas will be in vain.
In this post, we’ll go over the various components of exposure and how you can use them to create compelling images.
What is Exposure?
Exposure refers to the amount of light that a camera picks up when taking a photo. When you capture images, you expose a photosensitive digital sensor inside your camera to light.
Once you hit the shutter button, your image can take on one of the three states:
i. Overexposure – This happens when too much light reaches your camera’s sensor. In this case, the photo will be too bright.
ii. Underexposure – This occurs when too little light enters your camera’s sensor. In this case, the photo will be too dark.
iii. Proper exposure – This is the ideal outcome. It occurs when just the right amount of light reaches your camera’s sensor.
Properly exposed images have tonalities, textures, and colors that appear just the way they are in reality.
Photographers can choose to deliberately underexpose or overexpose their images to create a certain aesthetic. However, often, this will only be effective if the photographer knows what the proper exposure is. They typically start with the knowledge of the correct exposure; from there, they adjust their way towards their preferred exposure.
These kinds of decisions can result in the most breathtaking photographs. But, to break the rules effectively, you’ll first need to understand them. To do this, you’ll need to learn the three basic components of exposure: Aperture, Shutter speed, and ISO.
Aperture, Shutter Speed and ISO
Suppose we follow the path of light through the lens and into the camera. The light will first pass through the lens aperture, then the camera’s shutter, and finally into the sensor.
As the light travels through this path, each element (lens aperture, shutter, sensor) will determine the overall exposure of your image.
These components are controlled by three settings: Aperture, Shutter speed, and ISO. These three settings have a cause-effect relationship. That is, to register the same exposure, a change in one of the settings must be followed by a proportional change in at least one of the other settings.
Understanding the workings of these three settings is essential to controlling the outcome of your images. To take better photos, you must be able to adjust the Aperture, Shutter speed and ISO settings in a way to suit any lighting condition.
Embed This Infographic: How a DSLR Camera Works
Aperture is the diameter of the hole inside the lens of a camera. This hole can increase or decrease to let in more or less light into your lens respectively.The aperture is the equivalent of the pupil in our eyes. The eyes act as the lens for our bodies, capturing and recording information that is within our line of sight.
Our pupils are holes in our eyes, responsible for adjusting the amount of light that reaches our retinas.
Just like the pupil, the aperture inside the camera’s lens regulates the amount of light that reaches the camera’s sensor.
Besides regulating brightness, the aperture is also responsible for the amount of area in focus within images. A small aperture will keep a large area within a frame to be in sharp focus, while a large aperture will result in a smaller area within the frame to be in focus.
Aperture and Light
Similar to how our pupils adjust to the changes in light to create correctly exposed scenes, adjusting the aperture helps allow the right amount of light to enter the camera and create the proper exposure.
The only difference is that the changes in our pupils are instantaneous and automatic. Walk into a dark room, and your pupils will automatically dilate to let more light into your eyes. Or enter a brighter location, and your pupils will automatically constrict to allow less light into the eyes.
The aperture, on the other hand, is adjusted by you, the photographer. To get the proper exposure, you must know how small or big to set it.
Making the aperture smaller or larger will let in less or more light into the camera respectively once you hit the shutter button.
Let’s look at the two images below. These images were shot with two different apertures while holding the other settings (shutter speed and ISO) constant.
For the left image, I used a small aperture (f/13). In this setting, less light was allowed in the camera resulting in a dark image. For the right image, I used a larger aperture ( f/2.8). In this setting, more light was let into the camera resulting in a brighter picture.
What is an F-stop?
Aperture is measured in F-stops. F-stops measure how much light can reach the sensor. You’ll find aperture and F-stop sometimes used interchangeably.
The example images above demonstrate how decreasing your f-stop (increasing aperture) will result in brighter images.
To calculate the F-stop, take the focal length of the lens and divide it by the aperture diameter. Here’s the formula:
F-Stop = f/n
Where f is the effective focal length; n is the aperture diameter.
Suppose you have a 70mm lens at F/2, the aperture diameter will be 35mm, arrived at as follows:
70 / 2 = 35
Taking the same focal length of the lens (70mm) at F/16, the new aperture diameter becomes a smaller 4.375mm. Again, here’s how to arrive at the figure:
70 /16 = 4.375
From the calculations, it’s apparent that the larger the aperture diameter, the smaller the F-stop. Conversely, the smaller the aperture diameter, the larger, the F-stop.
What’s important is not to be able to make this calculation, but rather, to understand the theory behind it. Thus:
Large F-Stop = Smaller Aperture = Less Light
Small F-Stop = Larger Aperture = More Light
Other than letting in light to the camera, adjusting the aperture also controls another aspect of the image: Depth of Field (DoF).
What is Depth of Field?
The depth of field determines how much of your image will be in focus. That is, it determines the area between the nearest and farthest part of the image that appears sharp and in detail.
Images that are in focus are sharp with clear details. Those that are out of focus are generally blurry, with soft edges.
Aperture and Depth of Field (DoF)
The DoF varies as you change the aperture of your lens. Increasing the aperture will decrease your depth of field, often referred to as shallow depth of field. Conversely, decreasing your aperture will increase your depth of field, also referred to as deep depth of field.
Deep depth of field means that a greater area of the image will appear sharp and in focus. Shallow depth of field means that less area of the image will be sharp and in focus.
Let’s look at the images below.
The image on the left has a small aperture (f/13) and has a deep depth of field. For our purposes, I boosted the shadows of this image in photoshop. Though this image initially came out dark, notice that most of it are in focus and sharp. Also, notice the presence of grain (noise) in this image. Noise is visible because the image is underexposed. Because I increased the image’s exposure in Photoshop the presence of noise was amplified (more on this later).
The image on the right, on the other hand, has a large aperture and a shallow depth of field. Though it came out brighter than the left image, observe that most of it are out-of-focus and blurry. Also, notice that unlike the image on the left, noise is not visible in this image.
I mentioned earlier that Depth of field is the area between the nearest and farthest part of the image that appears sharp. To understand this better, I have cropped the image to where I have placed my focus when taking these photos (the middle of the frame).
Notice, while the area where I placed my focus (circled in blue) has remained sharp in both images, the foreground of the images have different levels of focus. While the foreground rocks on the left image are sharp, the foreground rocks on the right are blurry. The foreground is blurrier on the right image because it has a smaller area of focus (f/2.8) than the left image.
To simplify this relationship between the aperture and depth of field, think of it this way:
Small f-number = Small area focus or Shallow DoF
Big f-number = Large area Focus or Deep DoF
That said, choosing your aperture settings all comes down to two reasons:
1. To control the exposure of your images, or;
2. To set your depth of field.
Increasing the aperture of your camera’s lens increases your exposure while simultaneously creating a shallower depth of field. Meaning, you cannot capture maximum light and have a deep depth of field by only adjusting the aperture.
To capture a deeper depth of field without sacrificing exposure, you’ll have to use the other settings that control exposure – shutter speed and ISO.
The camera’s shutter is a barrier that opens and closes for a given amount of time. This barrier controls the amount of light that reaches the sensor. Shutter speed is a measure of how long the camera’s shutter will stay open.
The longer the shutter stays open, the more light that will hit the camera’s sensor, resulting in a brighter picture. The shorter the amount of time the shutter stays open, the less light will hit the sensor, resulting in a darker image.
Let’s examine the images below. The photos below were taken with two different shutter speeds while holding the other settings constant.
I shot the image on the left with a shutter speed of 2 seconds, while I shot the image on the right with a shutter speed of only 10 seconds. Notice that the picture where the shutter remained open longer is brighter than the one where it did not.
Shutter Speed Settings
In general, shutter speeds have a range of shutter speeds, from 1/4000th of a second to 30 seconds. After 30 seconds your camera’s shutter setting will turn into bulb mode. In this setting, your camera allows you to leave the shutter open for as long as you want.
Camera shutter speeds below one second are measured in fractions.
For example, if you set your shutter speed to 500 the shutter in your camera will be open for 1/500 of a second, or 0.002 seconds. Similarly, if you set your shutter speed to 30, the shutter will be open for 1/30 of a second, or 0.033 seconds.
The choice of shutter speed will often depend on your subject and the lighting conditions around you.
For instance, shooting at night, with reduced ambient lighting, requires slower shutter speeds to capture more light. While shooting wildlife requires fast shutter speeds to freeze motion and eliminate blur.
You can adjust your shutter speeds to be fast or slow depending on the visual story you’re trying to tell.
Shutter Speed and Motion
Using fast shutter speeds can completely immobilize a subject. When using fast shutter speed, the camera’s shutter closes before any movement is recorded by the sensor. This allows you to capture your subjects in crisp detail that would otherwise be impossible to see with the naked eye.
Slowing down your shutter speed, on the other hand, serve to record motion and leave blurred lines across the photo. Slow shutter speed means your camera’s shutter is open longer. Leaving the shutter open longer enables the camera to capture a moving object in multiple positions across the frame.
It’s important to remember that when shooting handheld (that is, without the use of a tripod), a shutter speed setting below 1/60 seconds will often result in motion blur. Slow shutter speeds also result in a blur if your subject(s) are moving such as the example image above.
The choice of shutter speed is about balancing between the amount of light and the motion you’ll see in your photo.
Slower shutter speeds will let you capture more light, though, by doing so, it will also register more motion blur. Faster shutter speeds will let you freeze motion, but will also reduce the amount of light that reaches your sensor.
To freeze motion without compromising exposure and focus, you’ll need to use one of the other elements of exposure – ISO.
Camera sensors have a natural sensitivity level referred to as Native ISO. Changing the ISO level will prompt the amplifier in the camera sensor to adjust the information gathered at the native ISO.
Higher ISOs enhance the data gathered by the camera’s sensor, resulting in brighter images. Lower ISOs, on the other hand, reduce the data collected by the camera’s sensor producing photos with less exposure and brightness.
Let’s look at the images below.
I took the left image with an ISO of 800 and the right image with an ISO of 3200. Noticeably, The higher ISO used the brighter the image will be.
So, naturally you think you would want to photograph at higher ISO numbers, but this is not always the case. Here’s why:
As you increase the ISO, you not only increase the exposure but also increase the appearance of digital noise. This increase in noise decreases image quality by introducing visible grain in the photo.
ISO and Light
Unlike aperture and shutter speed, ISO does not control the amount of light that enters the camera. It simply determines the brightness of a photo by altering the information that the sensor is gathering.
Increasing your ISO will reduce the amount of time required to reach a proper exposure. Let’s look at some examples. The images below were taken at night.
To get a good exposure without compromising sharpness, I had to use a small aperture and a slow shutter speed. To prevent motion blur, I also had to use a tripod (Recall: handheld shots get blurry at shutter speeds below 1/60 of a second). The resulting image is the one on the left.
However, say you don’t have a tripod. To reach the same exposure with the same level of detail, you will have to reduce your shutter speed. You can only do this by increasing your ISO as I did with the image on the right. Notice, however, that by doing so I also amplified the noise in the picture.
Understanding ISO and Digital Noise
I mentioned earlier that noise increases as you increase the ISO. So it’s advisable to use a lower ISO when possible to limit the noise in your photos.
By noise, what we are referring to are the visual distortions (grain or discolorations) sometimes found in photos.
To increase exposure without amplifying noise, consider using higher aperture or slower shutter speeds. If you prefer to avoid motion from slower shutter speeds, consider using a tripod.
The choice of ISO is about balancing exposure with the amount of noise in your photos. The perfect ISO level is one where the image has proper exposure with minimal digital noise.
What is the Exposure Triangle?
You may have heard of the exposure triangle. In case you are wondering what it is and how it works, I’ll briefly explain.
The Exposure Triangle is a visual representation of the three settings that determine exposure: aperture, shutter speed, and ISO.
The triangle is mainly helpful to remind you of the three camera settings that determine exposure. The shape is irrelevant and doesn’t tell you how to adjust your settings to reach a proper exposure. If you find the exposure triangle confusing, don’t worry. Understanding the Exposure Triangle is not necessary for understanding exposure; most people only use it as a memorization tool.
Putting It All Together:
Even though this model is often referred to as the exposure triangle, its components affect more than just exposure. The Aperture, Shutter Speed, and ISO also have an impact on the depth of field, digital noise and motion blur.
Understanding the inadvertent effects of changing each setting will help you create an image with desirable exposure and quality.
As a beginner, this all may seem overwhelming. Don’t worry. Your camera has built-in tools to help you determine the appropriate settings for the best exposure.
One of my favorite built-in camera tools is the camera light meter.
The Light Meter
The camera has a built-in light meter that reads the exposure of a scene. It offers an interpretation of what the appropriate aperture, shutter speed, and ISO setting will be.
To do this, the camera light meter measures the amount of light reflecting from the objects in the scene. These measurements are called exposure values.
The meter is a small series of bullets or blocks of lines accompanied by numbers located on the Live View display or the LCD screen on top of your camera.
Interpreting the Light Meter
The light meter’s exposure values can range from negative three (-3) to positive three (+3). Negative exposure values mean that a photo is underexposed, while positive exposure values mean that a photo is overexposed. A properly exposed photo will have an exposure value of zero.
For negative or positive exposure values, adjust the amount of light you are letting into your camera by using ISO, Aperture and Shutter speed.
The goal is to have the pointer on the light meter at or near zero when adjusting your exposure settings.
When to Override Your Light Meter
There are times when your camera’s light meter will give you an incorrect indication of how to set your exposure.
The camera’s light meter is programmed to interpret light as if it were reflecting off a neutral grey surface. That is, when taking a photo, your camera turns colors into tones of grey.
It then measures the amount of reflected light as a percentage. The camera meter’s baseline for proper exposure is 18% reflectance in visible light (mid-tone grey).
But our world is not grey; it is full of colors. Thus, there will be instances when the camera will provide an incorrect interpretation of reflectance.
If you take a photo of the snow, for example, your camera is likely to interpret your image as overexposed, even when its properly exposed. The misinterpretation is because snow is twice as bright as grey. But your camera’s light meter doesn’t intrinsically know that.
Conversely, images with a lot of shadows are bound to be interpreted by the light meter to be underexposed. If you take a photo of a black dog, for example, the light meter is likely to read your image as underexposed, even when it is properly exposed.
It’s important to understand that your camera’s built-in light meter does not see the world the same way as you do. Though it is built to assist you, it can never be you. It’s a useful tool, but it can only be as good as its user.
A Histogram is another built-in-tool within your camera to help guide you in measuring the exposure of your images. You can find the histogram for an image by selecting the playback button and then pressing either the up or down arrow until the histogram appears. Keep in mind that each camera is different and may require different steps to display the histogram.
A camera’s histogram is a graphical representation of how bright the pixels in your image are.
The x-axis measures the different values of brightness in a photo. The range of brightness can take on any value from 0 to 255; 0 being black and 255 being white. Generally, brightness values between 0 and 85 are considered shadows; values between 85 and 170 represent mid-tones, and values between 170 and 255 represent highlights.
The y-axis measures the total count of pixels at each brightness value. There is no set range on the y-axis. This is because determining the total number of pixels present in a photo is complex and difficult to measure. What’s important to know is that the higher you are on the y-axis, the more pixels that are present at that brightness value.
The tonal range of a photo is where the majority of your brightness values fall. For instance, in the histogram above the tonal range falls primarily in the mid-tones.
The tonal range can be found anywhere between two categories: high-key and low-key.
High-key images consist of mostly highlights; they are brighter and often overexposed. Low-key images consist of primary shadows; they are darker and often underexposed. The images that are neither high-key nor low-key consist mostly of mid-tones; these images are often properly exposed.
You can use the tonal range as a baseline for determining the exposure in your image.
Why You Should Use Histogram
A histogram is an important tool in determining the exposure and detail in your images.
Underexposed images have the majority of their pixels near or at the 0 value on the x-axis. When this happens, the curve in the histogram peaks to the far left. At brightness values near zero, pixels will have little to no detail.
Conversely, overexposed images have the majority of their pixels near or at 255 on the x-axis. When this happens, the curve in the histogram peaks to the far right. At brightness values near 255 or pure, pixels will also have little to no detail.
Properly exposed images have the majority of their pixels located in the mid-tones. When this happens, the histogram’s curve is often bell-shaped. These images will contain sufficient brightness and detail.
I want to point out that properly exposed images do not always take on a bell curve. The overall shape of the histogram will depend on the elements within a photo. Consider the following scenarios:
If you take a picture of a black wall, the histogram is likely to be shifted to the left. It is shifted to the left because the scene consists of primarily dark objects.
Conversely, if you take a photo of a white wall, the histogram is likely to be shifted to the right. It is shifted to the right because the scene consists of primarily bright objects.
When analyzing your histogram for the exposure, it is important to take into consideration what elements are present in your scene.
You’re probably here because you have recently decided to explore the world of photography. If so, I am glad that you have. Photography has changed my life in many amazing ways. And if you feel overwhelmed by all the information above, don’t worry. They look more complicated than they are. If you stick through this learning process, I promise you, it will be worth it.