ISO in photography is one of the three key elements of the exposure triangle, together with aperture and shutter speed. Understanding how these work together is essential for properly managing exposure (EV).
Learning how ISO works is crucial to gaining control over your photography and capturing well-exposed, impactful images.
Dive into this simple ISO photography guide, which will help you gain a better understanding of how ISO works in photographic exposure. I’ll explain everything you need to know about ISO, including what ISO means in photography, how it affects your photos, how it works, when to use higher ISO values and when to stick with lower ones. You’ll also learn how to balance the exposure triangle and how to choose the right ISO value based on your camera’s sensor.
What is ISO in Photography ?
The term ISO stands for “International Standards Organization” and represents the numerical value assigned to the sensitivity level of your camera’s sensor.
The ISO value indicates how well the sensor can capture light and convert it into an image. A low ISO setting, like 100 or 200, means the sensor is less sensitive to light, while a higher value, such as 800 or 1600, means greater sensitivity.
In photography, ISO is a tool used to brighten your image in low-light conditions or when you need a faster shutter speed. However, there’s one thing to be cautious about: digital noise. Using a high ISO sensitivity introduces digital noise, which reduces the quality of your photo. That’s why we can say that ISO plays a critical role in determining the final quality of your image.
Photographers have the option to adjust the ISO sensitivity, which directly affects image exposure. Shooting at ISO 50 delivers the highest image quality with no digital noise, but this setting requires a lot of light for proper exposure or a slower shutter speed. In low-light conditions, higher ISO values like 3200, 5000, or 6400 are used to increase sensor sensitivity and achieve a well-exposed photo. Essentially, increasing the ISO value reduces the amount of light needed to achieve proper photographic exposure.
How ISO is measured in digital cameras?
ISO is measured using numbers such as ISO 100, ISO 200, ISO 400, ISO 800, etc.
As you may notice, each ISO stop in photography doubles the previous number, effectively doubling the amount of light captured in the image with each step increase.
A lower ISO number means the sensor is less sensitive to light, requiring more light to achieve a proper exposure. On the other hand, higher ISO numbers increase the sensor’s sensitivity, making it easier to shoot in low-light conditions, though at the cost of introducing more digital noise.
The ISO scale uses an arithmetic progression to adjust the sensitivity of the digital sensor, starting from the lowest achievable ISO setting. Each time the ISO value doubles, the sensor’s sensitivity also doubles.
Most modern digital cameras offer ISO ranges from as low as 50 up to 126,000 or more. However, the most commonly used ISO values typically fall between 50 and 10,000, providing a wide range of options for different lighting conditions.
How to choose the right ISO setting
Just like aperture and shutter speed, there is no a “best” ISO value to set on your camera. The ideal ISO depends on the lighting conditions, the subject you’re photographing, and how you want to capture it.
That said, the best ISO value for achieving maximum image quality is the camera’s lowest native ISO, typically between ISO 50 and ISO 100. However, this is only suitable when lighting conditions allow and when the scene is stationary, without any fast-moving subjects.
Photography Tips and Tricks:
- When using a tripod, always set your camera to the lowest ISO value available. This helps reduce digital noise and improves the overall quality of your photo. With a tripod, you don’t need to worry about maintaining a minimum shutter speed (like 1/60) to avoid blurry shots, which is usually required when shooting handheld.
- However, for night photography, the situation is different. Even with a tripod, you may need to increase the ISO, especially in very dark locations, to achieve a properly exposed image, even if you extend the shutter speed for several minutes.
Understanding ISO might seem complicated, but I’ll simplify the reasoning for you: The ISO value in photography is chosen based on two factors: shutter speed and digital noise.
Choosing ISO based on shutter speed: If you’re shooting handheld without a tripod and the scene doesn’t provide enough light, you’ll need to increase the ISO to maintain a shutter speed of at least 1/60 of a second for a sharp image. Or, if you need to freeze a fast-moving subject in low light conditions, such as in wildlife photography, you must raise the ISO to keep a fast enough shutter speed.
Choosing ISO based on digital noise: In low-light conditions, like night photography when capturing the Milky Way, you need to increase the ISO to get a properly exposed image. However, there’s a limit, as increasing the ISO too much will introduce digital noise. As the ISO value rises, digital noise increases exponentially, reducing the overall quality of the photo.
Photography Tips and Tricks
So, my advice when shooting in low-light conditions is to find the highest ISO value your sensor allows to achieve a photo that is properly exposed with acceptable digital noise. This can usually be easily corrected during editing with software like TopazLabs DeNoise or through a proper workflow. Always remember that it’s better to have an image with more digital noise than one that is completely underexposed.
How ISO and Exposure Triangle are related in photography
As we have seen, the relationship between ISO, aperture, and shutter speed forms the exposure triangle, which determines the overall exposure of your photographs. Adjusting one of these settings affects the others, and finding the right balance is crucial to creating well-exposed images.
By setting a higher ISO, we can use faster shutter speeds and smaller apertures, which makes it ideal for freezing motion and increasing depth of field. On the other hand, setting a lower ISO may require longer exposure times or wider apertures to achieve proper exposure.
Understanding this balance is essential to making better decisions in the field, depending on what you want to capture.
Balancing ISO with Aperture and Shutter Speed
We’ll go over a few practical examples of how to set the ISO based on the scene you want to photograph to achieve a proper exposure and balance the exposure triangle.
Wide Landscape in Low Light Conditions
Imagine you’re facing a landscape with flowers close to you and mountains in the background, under dramatic skies with low light. You want to focus on the flowers to emphasize them but also capture the entire scene from the foreground to the background in sharp focus. To achieve this, you need a lot of depth of field, which means setting a small aperture (f/16). This will reduce the amount of light hitting the sensor. Since you’re shooting handheld, you can’t use a slower shutter speed than 1/60, so you’ll need to raise the ISO to balance the exposure triangle, achieving a proper exposure (EV).
Fast-Moving Subject
In this case, the most important factor of the exposure triangle to consider is the shutter speed. We need a fast enough shutter speed to freeze the motion of the subject and capture it in sharp focus (whether it’s a person, an animal, etc.). By increasing the shutter speed, less light enters the camera, so we need to balance the exposure triangle to achieve a proper exposure by raising the ISO and/or opening the aperture.
Night Landscape
In low-light conditions, such as when photographing the Milky Way or the Northern Lights, it’s essential to use a higher ISO value and also a larger aperture to allow more light to reach the sensor. Let’s say we are photographing the Milky Way without using an astro tracker. We are limited to around 20 seconds of exposure when using a wide-angle lens like a 14mm. Suppose the maximum aperture of our lens is f/2.8. Now we have two values that determine the exposure triangle: a shutter speed of 20 seconds and an aperture of f/2.8. To achieve the correct exposure (EV), we need to balance the exposure triangle with the third value, ISO. By increasing the ISO, we’ll obtain a proper exposure.
Keep in mind that there’s a threshold for increasing ISO, beyond which the sensor generates too much digital noise, resulting in a low-quality image.
How ISO and digital noise are related
The ISO value and digital noise are closely related, and this is one of the most important factors to consider when increasing the ISO. As we raise the ISO value, the camera artificially increases the amount of light, which leads to digital noise in the photograph.
The amount of digital noise at higher ISO values also depends on the type of digital sensor being used. Full-frame sensors with fewer megapixels (meaning less pixel density) create less digital noise compared to sensors with more megapixels.
This is why, in night photography, cameras with sensors that have lower megapixel density are preferred. A 24MP full-frame sensor is a great compromise. With fewer megapixels, the sensor is better at handling digital noise when the ISO is increased. With better sensors, you can even take great photos at ISO 8000.
Read more about digital noise in photography: “What is Digital Noise in Photography?”
Tips to choose the best ISO in Photography
In daytime landscape photography, the most commonly used ISO value is ISO 100. This is because a tripod is often used and the scenes are typically still, with no fast-moving subjects like animals or people. When shooting handheld, you need to choose the ISO sensitivity while keeping in mind the minimum shutter speed (usually 1/60 sec) to ensure a sharp image. So, if you notice your shutter speed is 1/20 sec, you’ll need to increase the ISO value to 200, 400, or whatever is necessary to reach at least a 1/60 sec shutter speed.
ISO Setting Explained
When to use low ISO setting:
- Landscape Photography (wide scenes, daytime)
Benefits: no digital noise, sharpness, maximum image quality
When to use High ISO setting:
- Night Photography (low light conditions)
- Wild life Photography / Sport Photography (fast shutter speed)
Benefits: low light photography, fast shutter speed
Drawbacks: digital noise to manage both during shooting and in editing
Conclusion
At this point, I hope this simple ISO photography guide has been helpful in better understanding how ISO works in photographic exposure.
Always use the lowest possible ISO based on what you want to photograph and the lighting conditions. However, if needed, don’t be afraid to raise the ISO, it’s better to have an image with more digital noise than a completely underexposed or blurry photo because you shot handheld with too slow of a shutter speed.
You can experiment with different combinations of ISO, aperture, and shutter speed. This will help you better understand these compromises and develop your artistic style.Photography tip: Keep an eye on the histogram while shooting to ensure the image is properly exposed.
