International Organization for Standardization

Topics Covered

1

What is ISO
2

The ISO scale
3

Base ISO
4

Grain and Noise
5

Where Does IOS come from?

What is ISO?

ISO is probably the easiest to understand in the triangle of exposure, so its a great place to start. In this section we will be referring to film quite a lot (because that’s where it started) but don’t worry if you are not a film photographer. All the content covered still relates to digital photography and works in very much the same way.

ISO is a scale that determines how sensitive your film or digital sensor is to light.

The ISO Scale

The ISO scale is a numerical system—typically ranging from 100 to 6400 or higher—that helps photographers adjust their exposure based on lighting conditions. You want to commit this scale to memory and the conditions you would use them in. This gets easier the more you do it. Every time you go into a new lighting condition… you want to start thinking… “What ISO should I start with?”

Mouse over the cards below to see where you would use the following ISO’s.

ISO 100

Sunny outdoor scenes, beach photography

ISO 200

Slightly overcast days, shaded outdoor areas

ISO 400

Cloudy days, indoor with good window light

ISO 800

Indoor events with lighting, early evening outdoor

ISO 1600

Night time street photography, indoor sports

ISO 3200

Very low light scenes, astrophotography

Base ISO

The lowest native ISO setting of a digital camera, offering the best image quality. This doesn’t apply to film photography because you can change your film, but in a digital camera, the Base ISO (the lowest ISO number your camera will do) will give you the greatest quality.

The Full Range

The ISO range above is the main one to remember. Its worth noting though that there are specialised films that go down to ISO 25 and in digital can go up to ISO 128000. These are for special ISO’s are for specialists cameras and situations and not all digital cameras will have. All cameras will have the range of ISO above so its worth just remembering these.

Grain and Noise

With all things in life, every decision comes with a trade-off—and photography is no exception. When we raise the ISO, we also invite something known as grain (in film) or noise (in digital) into our image. This grain or noise shows up as a speckling effect that gently erodes image quality. The higher the ISO climbs, the more pronounced this texture becomes, subtly—or sometimes not so subtly—blanketing the photo. See the images below to see a visual comparison of this.

Film Grain

With a high ISO, film grain makes the image make up of large dotes which reduces the sharpness of the image.

Digital Noise

With a high ISO, digital noise adds a colour speckling which also reduces the sharpness of the image.

So is noise/grain bad?

I’d say no—not inherently. It all depends on the situation and what you’re trying to capture. What feeling you want your image to evoke. Each side of the exposure triangle has its technical side (a scale) and its creative side—how it shapes the final image. With ISO, grain is its creative side. If you’re photographing a spider and want crisp detail in its eyes, grain probably works against you. But if you’re shooting backstage at a rock concert, grain can amplify the mood, adding grit and atmosphere that words alone can’t convey.

Low Noise – Low ISO

High Noise – High ISO

Where does the word ISO come from?

ISO in photography comes from the International Organization for Standardization, which unified earlier film sensitivity standards into one system in 1974.
Originally, film sensitivity was measured using two separate systems: ASA (American Standards Association) and DIN (Deutsches Institut für Normung). These were merged into a single international standard by the International Organization for Standardization (ISO) to simplify and unify exposure ratings across countries and manufacturers.

Before the ISO standard was introduced, different films from different manufactures and country’s would behave differently. This would make it very difficult to get consistent results while using different films. The ISO standard would mean your exposures would be remain consistent while using different brands of film. Today with digital photography the standard still stands so users who know photography, can use any brand of camera.

Interestingly, ISO isn’t actually an acronym. The organization chose “ISO” as a universal name derived from the Greek word isos, meaning “equal”—so it would be consistent across all languages, rather than varying like “IOS” in English or “OIN” in French. Not only that, ISO is used across many industries as the equal standard for quality and standards.