What Does ISO Stand For in Photography?
In photography, there are three basic elements that all work in tandem to control exposure. Shutter speed, f/stop, and ISO. That last one can be a little tricky to wrap your head around if you’re just starting out in photography or have only used automatic digital cameras in the past. So let’s get to the bottom of this key element of photography and understand once and for all: what does ISO stand for?
In short, ISO is the term used to indicate “film speed” in traditional photography. But if you’ve ever done a quick Google search of the term, you may have been frustrated if you wanted to know what it literally stands for. For that, we need a quick lesson in international diplomacy and nerds.
ISO stands for International Organization of Standards. But wait, wouldn’t that be IOS? That’s the diplomacy part. Because it’s a global organization, it’d have a different acronym in different languages. So rather than going by many names, they settled on ISO for everyone to use. It’s even on their logo.
And what exactly does any of that have to do with photography? Well, that’s the nerd part. See, nerds who like to begin their contribution to dinner party conversations with the phrase “well technically…” got together and developed standards to describe photographic film’s sensitivity to light.
Now that we’ve got the history out of the way, we can look at what ISO means for the practical photographer. Wistia describes it succinctly as follows: “the lower the ISO, the darker your image will be; the higher the ISO, the brighter your image will be.” To make that a bit more concrete, let’s imagine an example.
Let’s say you want to experiment with astrophotography. Nothing fancy, no special telescope attachments, just a tripod, a camera, and a clear dark sky. To take such a picture its best to think about your own eyes. When you go stargazing, it takes your eyes a bit to adjust, and as the first few minutes pass by, you can gradually see more stars. Why? Your pupils are dilating, letting in more light.
That’s an easy analogy to your camera’s aperture, the adjustable opening that controls the amount of light that comes in. Combined with shutterspeed, the amount of time the aperture is open, you have now controlled the total amount of light coming in. That’s where ISO comes in.
According to Astro Backyard, you’ll want an ISO of anywhere from 400 all the way to 1600 for night photography. That’s because you want a high sensitivity to the very limited amounts of light coming in.
ISO can very simply be described as a film’s sensitivity to light. A low ISO like 100 is appropriate for bright daylight photos. Since you have plenty of light to work with in daylight settings, you will pair that with a short amount of time to have the aperture open.
These days, if you just search the phrase “film grain” on Google, you’ll get many results on how to artificially add it back into a crisply captured digital image or video for artistic effect. However, before it was a trendy tutorial in Photoshop, it was a real artifact of the imperfections of traditional photography.
Film grain is caused by the irregularities in photochemical particles that are manipulated by exposure to light. The higher the ISO, the more likely the grain will be noticeable in the final developed photo. It’s kind of like if you were looking at an image made of sand and zoomed in enough to see the individual granules. In modern media, you’re most likely to encounter it not in its natural form but added to a digital creation for “texture.” Likely by someone who thinks vinyl records are superior because they’re “warmer,” whatever that means.
What happens on auto?
All this information is great if you’re using a traditional film camera with fully manual settings. But what exactly is a point-and-click automatic digital camera doing? It can seem like wizardry that with esentially no knowledge of photography you can still capture a beautiful picture. So what’s happening in the brains of a digital camera, and how does ISO come into play when there’s no physical film?
When the camera does all the work for you, we can broadly call that process autofocus, even though it’s doing a lot more than just bringing the image into focus. An internal sensor uses algorithms to determine how far to focus in the field of view. To make it simple, the camera’s computer does math to make a very clever guess at what you want. B&H Photo has a fantastic guide on understanding everything having to do with focus. There, they explain in excellent detail all the sensors, motors, and mirrors that work in tandem to do their magic.
Cool, now we have a basic idea of how autofocus works. But what about ISO? In a digital camera, like say your phone, what was once a pile of different types of film is now a slider on your screen. For a deep dive into the technology, including the underlying math, check out this section of the film speed Wikipedia page. But put simply, it doesn’t change the amount of light you capture, only f/stop and shutter speed do that. Rather it digitally alters the brightness of what you’ve already captured.
The last thing to know about digital ISO is that a higher value will result in more “noise,” which is analogous to film grain, as we discussed earlier.
To bring it all together, ISO is the oddly-named way we describe film’s sensitivity to light. Since the advent of digital photography, the term has been borrowed from the traditional physical medium and translated into a digital setting. It’s a core element to understand if you want to elevate your photography game. With a little experimenting, you can quickly get a grasp on the best ISO for whatever lighting situation you’re working in.