The three main settings you should take into account when exposing a photograph are the aperture, shutter speed, and ISO. These are commonly referred to as the “exposure triangle”, as one must achieve a balance between all three factors to achieve a well-exposed image. Today we will be talking about what is ISO, what it stands for, its effects, and how you can use it to your advantage to take the best pictures possible.
What does ISO mean?
The word ISO comes from the abbreviation used for the International Organization for Standardization. The founders of this organization chose the term “ISO” to abbreviate its name (rather than an acronym like IOS) inspired by the Greek word “isos,” meaning “equal.”
The organization sets and maintains a variety of industrial and commercial standards, including for photography. Previous camera standards ASA and DIN were combined to create the ISO standard in 1974. At its origins, ISO was a rating for the light sensitivity of photographic film (ISO 100, ISO 200, ISO 400, etc). The higher the ISO rating, the more sensitive the film was.
With the rise of digital photography, the term ISO was adopted as a measure of the sensor’s light sensitivity.
What is ISO in a camera?
In photography, ISO relates to a sensor’s (or film’s) sensitivity to light. A lower ISO setting makes the sensor less sensitive to light, meaning it either needs more illumination or a longer shutter speed to properly expose an image. Increasing the ISO makes your sensor more sensitive to light, allowing you to shoot in darker environments, with tighter apertures, and/or using faster shutter speeds.
How is ISO measured?
ISO is measured in numbers. While manufacturers used to stick too ISO 100, 200, 400, 800, 1600, and so on (doubling in value), things have changed with more recent cameras. Smaller increments have been introduced for better refinement, but the concept is the same. ISO 100 is half as sensitive as ISO 200, which is also half as sensitive as ISO 400.
The effects of changing the ISO value are simple to understand. A higher ISO setting will make a sensor more sensitive, and therefore, make an image brighter. At the same time, increasing the ISO creates more grain or noise. It is not mentioned often, but a higher ISO can also deteriorate dynamic range, which is a more important reason to stay as low as possible.
Look at the images below to see an example of differences between low ISO and high ISO levels. These images were not altered with editing. They were simply thrown in Lightroom for cropping so you can better see the differences in grain. Furthermore, it must be noted they were shot with a Nikon D610, which has a full frame sensor. Such bigger sensors are significantly superior when handling noise in higher ISO levels. The differences will be more obvious when using smaller sensors.
With that in mind, the images above show a significant difference in image quality. Not only is the high-ISO one grainier, but quality in colors and dynamic range have changed.
When should I increase the ISO?
I have said it time and again: a good photograph can’t be ruined by grain or noise. This is because there are more important factors to consider, such as composition, subject, meaning, and many other intangibles that make an image outstanding. Don’t be scared to increase the ISO if you need to… but only if you really need to.
A lower ISO will create a better-looking image, so our general advice is that you only increase ISO when totally necessary. If there is not enough light, you need a tight aperture, or want to keep a faster shutter speed, then your only option is to increase the ISO. If you can, try to keep your ISO as close to your lower option as possible, which is usually ISO 100.
