Photography Basics: Understanding Camera ISO

In a previous article we have discussed the meaning of camera exposure and learnt that camera ISO is a very important factor in the exposure triangle. But what does camera ISO mean? And how is it different in a digital camera and a traditional analogue camera? I will try to discuss camera ISO in more detail and see how its setting can affect the final exposure value.

Film ISO

Actually, camera ISO is one of the old concepts in film photography that is utilized in digital photography. Film photography refers to the sensitivity of the film to light exposed by the camera lens. On old roll films, you can find the ISO number written on the film and you have to choose the ISO based on your needs.

Film camera ISO
Photography film sensitivity to light (ISO)

For example, low light photography requires a high ISO value to enable high sensitivity to light; however, it produces noise and grain on the final image. On the other hand, you can use low ISO films in high light photography, such as outdoor photos that do not require high film sensitivity. The produced images have fine grains and less noise than high ISO films.

Digital camera ISO

In digital cameras the ISO concept is still applied with different methodology, as the ISO in a digital camera refers to the camera sensor’s sensitivity to light. So, the camera sensor replaced the film in the old cameras, and the results of the digital camera ISO settings are the same as they were in old film cameras.

The figure below shows the noise amount produced by a low camera ISO setting on the left and a high ISO setting on the right.

Camera ISO noise
The right sample shows low ISO value (less noise) and the right sample shows high ISO value (high image noise)

Generally, a camera’s exposure range is between 100 and 3200, and the common range that helps preventing noisy images ranges between 100-400. Many digital cameras have an auto ISO mode, which lets the camera determine which is the suitable ISO setting for your shot.

How to choose the proper camera ISO value?

The tricky part here is how to use the best combination of ISO, shutter speed, and Aperture to get a well-exposed shot. For example, you can use a high ISO or low shutter speed to get more light into the camera and produce a bright image. However, in some situations, you will have to choose either of them to get the proper exposure.

Let’s say you are shooting a sports event at night where the players are moving around. In this situation, you will not be able to use a slow shutter speed as the elements in your scene are moving around. So, you will need to increase the camera’s ISO sensitivity, which subsequently produces a noisy shot. In this example, you can reduce the noise by decreasing the ISO and use a light source to apply more light to the scene, or decrease the shutter speed a little and use a tripod to reduce camera shake.

In another example of shooting a dark still life scene, you can use a combination of a slow shutter speed and high ISO to get a well-exposed shot with low noise.

camera ISO example
The left side shows high ISO value and the right side shows low ISO value

Generally, there are some situations where you have to use high camera ISO, such as at birthday parties, concerts, and art galleries. Camera ISO is one of the essential settings in your digital camera. Understanding it and how it affects the shot’s exposure helps you to create professional photos. Also, you might want to check the new Adobe Photoshop CC features and how you can use Camera Raw to modify photo exposure.

Next photography lessons:

Photography basics 1: Tips to Choose Your First DSLR Camera

Photography basics 2: Understanding Camera Exposure

Photography basics 4: How Does Your Camera Image Stabilizer Work?

Photography basics 5: Understanding White Balance

Photography basics 6: How Your Digital Camera Sensor Works