The Exposure Triangle — Clearly Explained

Taking photos has never been easier, especially with the convenience of our smartphones. For a long time, I too believed capturing stunning images was as simple as pressing a button on the screen. However, my perspective shifted dramatically after purchasing my first camera for a trip to Italy. I snapped over 1,000 photos of majestic architecture and breathtaking natural landscapes, only to discover that nearly all of them turned out excessively dark.

This frustrating experience motivated me to get into the field of photography, I know very well how confusing it can be for an absolute beginner to navigate through the camera user manual and try to figure out which button to press. So I decided to create this guide in plain English (NOT in photographer language) to help you take photos with desired brightness.

This article is organized in the structure below:

section 1. What is exposure?

section 2. Path of light and exposure triangle

section 3. Using F-stop/shutter speed

section 4. How to choose the right shooting mode

I will try my best to keep things simple and intuitive but we will still need to learn a few technical terms, which will be marked in bold and Italics.

This is a hands-on guide, so I recommend you have your camera on standby while you read this article.

1. What is exposure?

A camera is a device that allows light into the lens, and the sensor inside translates the incoming light into an image, this process is called exposure. Exposure directly impacts the brightness of the photo.

When a photo appears too dark, it is described as under-exposed, indicating that insufficient light has reached the camera’s sensor. Conversely, a photo that is excessively bright is termed over-exposed, a result of too much light hitting the sensor. The ideal scenario is a properly exposed photo, where the brightness levels are just right, capturing the scene effectively.

Consider the examples below: both the under-exposed and over-exposed images fail to preserve essential details and colors. In contrast, the central image, with proper exposure, clearly outshines the others in terms of detail and overall visual appeal.

Now the question is how do we know if a photo is properly exposed? Often, the simplest method is just to use your eyes. Since everyone has different preferences, a photo that looks bright enough to you may well be perfectly exposed for your needs.

Besides this subjective approach, cameras offer a more objective way to gauge exposure through the Exposure Value (EV benchmark). You don’t need to understand the math behind it right away, but knowing how to read this can be incredibly useful.

On Sony cameras, for example, the EV scale typically appears at the bottom middle of the screen, marked by a specific icon. The user interface (UI) might vary across different brands, but the underlying concept remains consistent — providing a clear, numeric indication of exposure levels.

EV benchmark on Sony cameras

Now how to read EV benchmark? Reading the EV benchmark is quite straightforward. The value next to the M.M. icon represents the exposure level, which typically ranges from -2 to +2:

• Zero (0) indicates that the photo is properly exposed.
• Positive Values (+0.1 to +2) suggest that the exposure level is increasing; the higher the number, the more over-exposed the photo is. For example, +0.3 means there is a slight excess brightness, while +1.8 indicates significant over-exposure.
• Negative Values (-0.1 to -2) indicate decreasing exposure levels; the lower the number, the more under-exposed the photo is. For instance, -0.3 suggests a slight lack of brightness, and -1.8 implies the photo is quite under-exposed.

This system helps photographers quickly adjust their settings to achieve the desired brightness for their images.

Consider the set of three photos displayed below, each capturing the same subject. By now, you might recognize that one is under-exposed, one is over-exposed, and another is properly exposed. Let’s use the EV benchmark to understand why.

EV benchmark highlighted in red box

• The first photo has an EV benchmark of -1.3; it’s under-exposed.
• The second photo shows an EV of 0.0; it’s properly exposed.
• The third photo is marked with an EV of +1.7; it’s over-exposed.

A helpful analogy is to think of the EV benchmark as a thermometer measured in Celsius:

• Values below 0, like sub-zero temperatures, indicate a lack of warmth from the sun, resulting in darker, “colder” photos.
• Values above 0 resemble higher, “hotter” temperatures where too much sun results in blinding, over-bright images.

Just as temperatures dictate our perception of cold and hot, the EV scale helps us gauge the “thermal” condition of our photos in terms of exposure.

Remember, the EV benchmark is merely a tool for guidance. If you are satisfied with how your photo looks, there’s no need to strictly adhere to what the EV reading suggests. Often, photographers intentionally over-expose or under-expose their images to convey specific moods or artistic expressions.

Hands-on Exercise: Locate the EV benchmark display on your camera’s screen. Take some time to familiarize yourself with the icon used for EV and the values associated with it. This will help you effectively interpret and utilize these readings in your photography.

2. Path of light and exposure triangle

Now that we’re familiar with the concept of exposure and how to measure it, let’s explore how light travels inside a camera. Mastering this will enhance our ability to adjust exposure settings with precision.

Key Components Influencing Light Capture: aperture, shutter and CMOS/CCD Sensor.

2.1 Aperture

This is the circular opening within the lens that can vary in size. When the aperture is wide open, it allows more light to pass through; when it’s narrow, less light enters. The aperture size is controlled through the F-stop value, denoted as f/xx (e.g., f/2, f/3, f/8). Crucially, the F-stop number is inversely related to the aperture’s size — a smaller F-stop number means a larger aperture, allowing more light to reach the sensor, and vice versa.

Hands-on Exercise: Adjust the F-stop setting on your camera’s control panel from the lowest to the highest value. As you make these changes, carefully observe how the brightness of your image and the EV (Exposure Value) benchmark are affected.

2.2 Shutter

The shutter is a crucial component located just behind the camera lens. If you detach the lens from your camera, you can see the shutter on the main body. It resembles a small gate or curtain and plays a vital role in exposure by controlling the duration that light hits the camera sensor.

Use DSLR Cameras as an example, How does the Shutter Work?

• Default Position: When your camera is on and you’re composing your shot, the shutter remains closed. This prevents light from reaching the sensor prematurely.
• Action Upon Release: Upon pressing the shutter button, the shutter quickly opens and then closes. The period during which the shutter is open is known as the shutter speed, which is measured in seconds.
• Speed Range: Shutter speeds can range from as fast as 1/4000th of a second to as long as 30 seconds. This setting is adjustable via the camera’s control panel.

how does shutter speed impact exposure?

• Longer Shutter Speeds (e.g., 1 second): The shutter stays open longer, allowing more light to enter. This is ideal for low-light conditions or for creating effects like motion blur in flowing water.
• Shorter Shutter Speeds (e.g., 1/1000th of a second): The shutter stays open for a brief moment, letting in less light. This is perfect for freezing motion, such as capturing a fast-moving athlete without blur.

Hands-on Exercise: Navigate to the shutter speed settings on your camera’s control panel. Gradually adjust the shutter speed from the shortest to the longest duration available. As you alter the settings, pay close attention to the changes in the brightness of your image and the readings on the EV (Exposure Value) benchmark.

2.3 CMOS/CCD Sensor

The CMOS or CCD sensor is the heart of a digital camera, responsible for converting light into an image. These sensors are pivotal in determining image quality.

• Full Frame vs. Half Frame: When we refer to full frame and half frame cameras, we’re discussing the size of the CMOS/CCD sensor. Full frame sensors are larger and capture more light, which generally allows for better image quality with greater detail and less noise compared to half frame (APS-C) sensors.
• ISO Settings: The sensitivity of the CMOS/CCD sensor to light is adjusted through the ISO setting, accessible from the camera’s control panel. Increasing the ISO value heightens the sensor’s sensitivity, making the photo appear brighter, which is particularly useful in low-light conditions. However, higher ISO settings can also lead to more image noise, which appears as graininess in the photo.

Hands-on Exercise: Locate ISO setting on your camera’s control panel, and slowly adjust ISO from lowest to highest available. As you alter the settings, observe the changes in the brightness of your image, and the readings on the EV (Exposure Value) benchmark. Pay special attention to the appearance of noise in the image as the ISO level rises. This will help you understand the trade-off between brightness and image quality.

2.4 how light travels inside the camera

Let’s explore how light navigates through a camera to produce an image. Refer to the illustration below for a visual guide. Imagine there are 1000 units of light available in the external environment:

Through the Lens and Aperture:

• As light enters through the lens, it encounters the aperture. If the aperture is not fully open, a significant portion of the light might be blocked. For instance, assume the aperture allows only 400 out of the initial 1000 units of light to pass through, blocking the remaining 600 units.

The Role of the Shutter:

• The light then reaches the shutter, which controls the duration that light is allowed to hit the sensor. Suppose the shutter opens for 1/1000 of a second. During this brief moment, it might only permit 200 of the 400 units of light to pass through to the sensor.

Capture by the CMOS/CCD Sensor:

• The 200 units of light that pass the shutter finally reach the CMOS or CCD sensor. The sensor captures these light units and converts them into an electronic image that you see on your camera or download onto your computer.

Summary: Achieving Proper Exposure

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To capture a well-exposed photo, it’s crucial to manage the amount of light that reaches the camera’s sensor. Since external light conditions are beyond our control, we must adjust our camera settings accordingly.

Key Elements of Exposure Control:

• Aperture (F-Stop): Adjusts the size of the lens’ opening, controlling the volume of light that enters.
• Shutter Speed: Dictates how long the shutter stays open to expose the sensor to light.
• ISO: Regulates the sensor’s sensitivity to light.

Together, these settings form the Exposure Triangle, a fundamental concept that allows photographers to balance the light dynamically according to varying conditions. By manipulating aperture, shutter speed, and ISO, you can freely fine-tune your camera’s exposure to match your artistic vision.

3. Fine-Tune Exposure

As discussed in the previous section, F-stop, shutter speed, and ISO significantly influence exposure. But how do we decide which setting to adjust when we need to modify the amount of light captured? Should we select F-stop, shutter speed, or ISO randomly, or adjust all three simultaneously?

To address these questions, it’s essential to consider the specific impacts of each setting beyond just exposure. While we know that a high ISO can introduce noise and degrade image quality, let’s explore the unique effects of adjusting the F-stop and shutter speed.

3.1 F-stop

let’s start from F-stop. Beyond regulating the amount of light that passes through the lens, F-stop has its own special superpower on the clarity/sharpness/blurriness of the background (which is measured by depth of field) in the photo.

• Lower F-stop Numbers: These settings open the aperture wider, allowing more light to enter and causing the background to appear more blurred (creating a shallower depth of field). This effect is perfect for highlighting the subject against a soft, indistinct backdrop.
• Higher F-stop Numbers: These settings narrow the aperture, reducing the amount of light and producing a sharper background (resulting in a deeper depth of field). This is ideal for landscape photography where the goal is to keep everything in clear focus.

The main goal of these 2 photos is to show the impact of F-stop on depth of field, the reason why they have different shutter speed and ISO is that to obtain 2 properly exposed photos with different F-stops, shutter speed and ISO need to be adjusted too, otherwise the photo on the right side would be under-exposed had I used the same shutter speed and ISO from left photo

In the example above, the main subject of my photograph is the vase, while the elements in the background, including a green wooden cow toy (let’s call it “Moo”) and a cabinet, play a secondary role.

• Photo on the Left (F-stop at 4.5): By setting the F-stop to 4.5, the aperture widens, allowing more light and creating a very blurry background. This shallow depth of field makes it difficult to discern the details of “Moo” and the cabinet behind it. The background compression obscures the spatial relationships, challenging our perception of the distances between the cabinet, “Moo,” and the vase. However, this effect helps the vase to stand out prominently, drawing more attention to it as the focal point.
• Photo on the Right (F-stop at 11): With the F-stop increased to 11, the aperture narrows, lessening the light intake but capturing more background details. The increased depth of field clarifies the spatial distances between the cabinet, “Moo,” and the vase. Although this setting provides a clearer view of the background, “Moo” becomes slightly more distracting, potentially diverting attention away from the vase.

To summarize, F-stop does the following to our photos:

Hands-on Exercise: Find a small object (for example, a mug) and place it near your camera, keep your camera focused on the small object while adjusting the F-stop setting on your camera’s control panel from the lowest to the highest value. As you make these changes, observe the background’s blurriness. If you don't see a noticeable change in background blurriness, try to shorten the distance between your camera and the object, this should enhance the depth of field effect, making the variations more apparent.

3.2 Shutter Speed

Here comes shutter speed! There are only 2 things to note, safe shutter speed and Taking Time-Lapse Photos with Slow Shutter Speeds.

3.2.1 Safe Shutter Speed

When you hold a camera and press the shutter button, slight movements are inevitable. If the shutter speed is too slow — say, 5 seconds — the shutter stays open long enough that any minor hand tremors will blur the entire photo. While using a tripod can stabilize the camera and prevent this, carrying one at all times isn’t always practical.

Defining Safe Shutter Speed: Safe shutter speed is the slowest shutter speed at which you can hold the camera in your hands and still capture sharp, clear photos. This threshold varies among photographers depending on how steady you can hold the camera and the weight of the camera itself.

Personal Example

• For Light Cameras: With my lightweight Sony zv-1f, I’ve found my safe shutter speed to be around 1/60 of a second. Therefore, I ensure the shutter speed is faster than 1/60 second when I’m not using a tripod.
• For Heavier Cameras: When I use heavier cameras, the required safe shutter speed increases to about 1/100 second to compensate for the additional instability from the extra weight.

Hands-on Exercise: Determining Your Safe Shutter Speed. You can establish your own safe shutter speed through practice and experimentation. Try taking photos at various shutter speeds and note at which point your photos begin to show blur from hand movement. This trial-and-error process will help you find the optimal speed for stable, hand-held photography.

3.2.2 When to Use Slow Shutter Speed

When to use slow shutter speed? short answer: When we want to take time-lapse photos. To capture effective time-lapse images, utilize a very slow shutter speed and secure your camera on a tripod to prevent any movement.

Consider the examples below: the left image was taken with shutter speed of 5 seconds, and the right image was taken with shutter speed of 1/4 second, they show a different level of motion blur and time compression.

Hands-on Exercise: Use your creativity to experiment with various slow shutter speeds to discover unique creative effects. Adjusting the exposure time allows you to capture everything from smooth water movements to light trails and more.

3.3 F-stop/Shutter Speed/ISO Adjusting Sequence

Now back to the questions:

how do we decide which setting to adjust when we need to modify the amount of light captured? Should we select F-stop, shutter speed, or ISO randomly, or adjust all three simultaneously?

I hope you already know the answers.

Here is what I usually do in 3 different scenarios:

Scenario 1. Take a landscape photo on a gloomy day

First, I set ISO to 1500. Compared to using a low ISO (i.e. 300), ISO 1500 offers me more flexibility on F-stop and shutter speed without causing lots of noticeable noise points.

Second, I adjust F-stop to a large value, say F8.0, to achieve deeper depth of field for landscape photos.

Now if the photo looks under-exposed, I would slow down the shutter speed to allow more light to hit the sensor. If at my safe hand-held shutter speed (1/60th of a second), the image is still too dim, it’s time to reassess. I would consider increasing ISO or decreasing F-stop, or both.

The goal is to find the perfect balance among image quality, depth of field, and exposure to create the desired photographic outcome.

Scenario 2. Take a clear shot of a high speed moving car

First, I set ISO to 1500.

Second, I set shutter to a high speed, say 1/3200th of a second.

Now the photo may be too dark, so I decrease F-stop. In the case that with smaller F-stop we still cannot achieve good exposure, I would try to increase ISO or slow down shutter speed.

Scenario 3. No specific requirements, just want to take a nicely composed and well exposed photo

First, I set ISO to 1500.

Second, sequence of adjusting F-stop or shutter speed does not matter that much here, as long as the photo is properly exposed and shutter speed is faster than safe shutter speed if not using a tripod.

Hands-on Exercise: try taking photos of different scenes and practice adjusting F-stop, shutter speed and ISO in different order, observe how it impacts your photo.

4. How to choose the right shooting mode

Most cameras nowadays offer the following shooting modes:

Manual mode: As the name suggests, Manual mode requires you to adjust the ISO, F-stop, and shutter speed manually. This mode offers the highest level of flexibility, allowing you to tailor the exposure settings precisely to your vision. However, mastering the exposure triangle — balancing ISO, aperture (F-stop), and shutter speed — can be time-consuming, particularly for those new to photography.

Given its complexity, Manual mode may not be the best choice for capturing spontaneous moments, as adjusting the settings can be too slow to react quickly to unfolding events.

Shutter priority mode: it allows you to select the shutter speed manually, while the camera automatically adjusts the F-stop and ISO to maintain optimal exposure. This mode is particularly valuable when you need to quickly capture images at specific shutter speeds.

Practical Example: Imagine you’re at an F1 race, where conditions change rapidly from dark to bright as cars speed along the track. To capture crisp images of the high-speed action, you would need a very fast shutter speed. Shutter Priority mode is ideal in this scenario because it swiftly adapts the exposure when moving from darker to brighter areas of the track, unlike Manual mode, which may not adjust quickly enough.

A potential drawback of Shutter Priority mode is that the ISO might be automatically increased to compensate for fast shutter speeds, especially in lower light conditions. This can lead to increased noise in the images, which might affect image quality.

Aperture priority mode: similar to shutter priority mode, here we have the flexibility to set F-stop as we wish, the camera would automatically adjust shutter speed and ISO to achieve optimal exposure. This mode is particularly beneficial when you need quick shots with specific depth of field requirements.

For example, consider you’re hiking through picturesque mountain terrain and want to capture expansive landscape shots. By setting the F-stop to a higher number in Aperture Priority mode, you can achieve a greater depth of field, ensuring that both the foreground and background remain in sharp focus. This setup allows you to continuously take photos as you move along the trail without having to manually recalibrate exposure settings for each new scene, unlike in Manual mode, where constant adjustment could significantly slow you down.

Intelligent auto mode: while shutter priority and aperture priority modes can be considered as half auto half manual modes, intelligent auto mode is the full automatic mode. With intelligent auto mode, we don’t need to adjust anything, the camera will automatically adjust F-stop, shutter speed, and ISO to achieve optimal exposure.

Intelligent auto mode is useful if you don’t have specific requirements for shutter speed or F-stop, and when you want to take quick shots.

Potential issues for aperture priority mode and intelligent auto mode is that ISO may be automatically set too high and results in lots of noise points, or shutter speed may be automatically set too slow (slower than your safe shutter speed), which might end up giving you all blurry photos.

Summary:

Hands-on Exercise: experiment with different shooting modes and familiarize yourself with their use cases.

One thing to note, in shutter priority, aperture priority, and intelligent auto modes, camera would automatically adjust to optimal exposure. By default, optimal exposure is when EV benchmark is zero. Unless you use exposure compensation to set optimal exposure to a different value.

What exactly is exposure compensation, and why is it necessary? Can cameras automatically achieve optimal exposure under all conditions, and what are the implications if they don’t? Furthermore, how does the EV (Exposure Value) benchmark function in practice?

To address these questions, we need to explore several fundamental concepts about how cameras measure and adjust exposure. These topics, along with detailed explanations, will be covered thoroughly in my upcoming post.