In Part 1 of Exposing The Triangle: The Exposure Triangle for Beginners, we went over the basics of the Exposure Triangle; what it is, the different elements and how they impact proper exposure. In this lesson, we are going to cover ISO and its impact on the overall process.
What is ISO?
ISO refers to the sensitivity of the camera's sensor to light. It is measured in numbers, with a higher ISO number indicating greater sensitivity to light and a lower ISO number indicating less sensitivity to light.
How does ISO impact exposure?
As stated in our overview of the Exposure Triangle, it is important to balance the relationship between all 3 elements of exposure: aperture, shutter speed and ISO. In certain environments, the photographer may encounter shooting situations that are less than ideal for proper exposure. A prime example would be a dimly lit room where aperture values are maxed out and too slow of a shutter speed will result in unwanted motion blur. If, in this situation, natural or artificial lighting was unavailable, the photographer could boost the camera's ISO to a point at which they are able to achieve the proper exposure or adequate shutter speed to reduce the likelihood of motion blur.
Another situation in which ISO impacts exposure would be in bright conditions where the photographer wants a shallow depth of field (wider aperture, more light). In this case, instead of increasing ISO, the photographer would decrease the ISO. When the aperture lets in too much light and there's a risk of overexposure, the photographer would need to adjust the exposure triangle to maintain proper exposure. One way to do this is by decreasing the ISO to balance out exposure and prevent the image from becoming too bright.
Benefits of ISO
Back in the Olden Times (aka the film era), cameras were limited to what "ISO" they could shoot at. Film stocks were rated at different film speeds or ASA (American Standards Association). Most photographers would use different film stocks based on the shooting conditions they encountered. For example, when shooting in bright daylight, they may use a 50 ASA (low sensitivity to light) film, or if they were shooting indoors, maybe a 800-1600 ASA (more sensitivity to light). In the event you were shooting under conditions that were not favorable to your film speed, you were kind of out of luck. Enter digital cameras and ISO. Now, all a photographer needs to do is simply change the ISO to achieve the required exposure. This increases speed and efficiency when photographing different events in which speed and accuracy is critical. By increasing or decreasing ISO, the photographer can maintain the desired shutter speed and aperture to maintain exposure and get the type of image they desire. Also, most modern cameras have a wide range of ISO values. On average, ISO can range from 50 to 51,200! Some cameras are even able to go beyond that. Film stocks, on the other hand, typically only range from 50-3200 ASA. ISO FTW!
Drawbacks of High ISO
Despite being a good method of achieving proper exposing in low light situations, there is an unwanted side effect of using high ISO; reduced image quality. By increasing the ISO setting on your camera's sensor, you are basically telling the camera's sensor to amplify the signal it receives from the light entering the lens. This amplification results in a brighter image, even in low-light situations where there isn't enough natural or artificial light available to achieve a proper exposure with a lower ISO setting. The trade-off of increasing ISO, however, is that it also amplifies any noise or grain that may be present in the image. This can result in a loss of image quality, particularly in the form of reduced sharpness and detail, as well as a decrease in dynamic range.
To mitigate these effects on image quality, the photographer can reduce the need for high ISO by:
Using a wider aperture so that more light hits the camera sensor.
Slowing down the shutter speed so that more available light can hit the camera sensor over a longer period of time. A tripod may be required to reduce camera shake in this situation.
Adding a light source such as flash, continuous or natural light.
How to change your camera's ISO setting
The process of changing ISO varies from camera to camera. But generally there are 3 methods:
A dedicated button on the camera body that is either native or configurable.
A dial or wheel.
A setting within the camera menu.
Auto ISO
Most cameras also come with an Auto-ISO feature. Auto-ISO is where the camera decides the correct ISO value based on the aperture and/or shutter speed. In situations where Auto-ISO is off and the photographer controls the value, the camera will do its best to manipulate shutter speed and/or aperture (depending on the shooting mode) to achieve the correct exposure. In some shooting conditions, this is not possible. The camera will usually warn the photographer through some visual or auditory alert that exposure is not correct and additional adjustments are needed.
Conclusion
In conclusion, ISO is a critical component of the Exposure Triangle, allowing photographers to adjust the sensitivity of their camera's sensor to light. By increasing or decreasing ISO, photographers can achieve proper exposure in a range of lighting situations and maintain desired shutter speed and aperture. The benefits of ISO are numerous, including increased speed and efficiency when photographing different events. However, high ISO settings can result in reduced image quality, including noise and grain. Photographers can mitigate these effects by adjusting aperture, shutter speed, or adding light sources. Overall, understanding and mastering the use of ISO is essential for photographers to achieve the desired results in their images.
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