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What is ISO in photography? Everything you need to know

ISO is the main reason why images have noise!

Published onJanuary 9, 2022

Edgar Cervantes / Android Authority

When exposing a photograph, the three main settings you should consider 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 ISO is, 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?

DSLR being held by a kid
Edgar Cervantes / Android Authority

The word ISO comes from the abbreviation used by the International Organization for Standardization. The founders chose the term to abbreviate its name (rather than an acronym like IOS) inspired by the Greek word “isos,” meaning “equal.”

The organization sets and maintains various industrial and commercial standards, and the photography market is one of them. 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, 200, 400, etc.). The higher the rating, the more sensitive the film was. We now use the same term and standards to measure a camera sensor’s light sensitivity, given the rise of digital photography.

Before we move on: Other photography terms you should learn

What is it?

The Exposure Triangle explaining what is ISO, aperture, and shutter speed.

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 expose an image properly. Increasing the setting makes your sensor more sensitive to light, allowing you to shoot in darker environments, with tighter apertures, or using faster shutter speeds.

Important: How to shoot photos in manual mode

How is it measured?

ISO is measured in numbers, usually multiples of 100. While manufacturers used to stick to 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, and now it’s common to see ISO measurements like 125, 160, and more. The concept remains the same, though. ISO 100 is half as sensitive as 200, which is also half as sensitive as 400.

The effects of manipulating ISO

The effects of changing the 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 isn’t mentioned often, but a higher ISO can also deteriorate dynamic range and colors. These are important reasons to keep ISO as low as possible.

Related: What is dynamic range in photography?

Look at the images above to see an example of differences between low and high sensitivity levels. We didn’t make any edits to these images. I cropped them so you can better inspect the differences, though. Furthermore, we must note we shot these photos using a Nikon D610, which has a full-frame sensor. Such bigger sensors are significantly superior when handling noise. The differences will be more pronounced when using smaller sensors, such as ones found on smartphones.

With that in mind, the images above still show a significant difference in image quality. Not only is the high-ISO one grainier, but the quality in colors and dynamic range have changed.

When should I increase the ISO?

Aperture priority DSLR shooting mode dial
Edgar Cervantes / Android Authority

I have said it time and again: grain can’t ruin a good photograph. Composition, subject, meaning, and many other intangibles are far more critical. Play with the sensitivity; just be conscious of why you’re doing it, and its consequences.

Grain can't ruin a good photograph.Edgar Cervantes

A lower ISO will create a better-looking image, so our general advice is that you only increase the parameter when totally necessary. If there is not enough light, you need a tight aperture, or want to keep a faster shutter speed, your only option is to increase sensitivity.

Of course, there are some things you can do to keep the ISO as low as possible. You can often add artificial light to the scene, or slow down the shutter speed while adding more support with a good tripod.

Next: Photography tips that will instantly take your images to the next level

Are you looking to improve your photography knowledge, skills, and equipment further? We have plenty of excellent photo content for you. Check out some highlights below.

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