How to Use ISO Settings in Digital Photography

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ISO should be one of the easiest aspects of digital photography to master, but many beginners in photography still have a hard time understanding this fundamental camera setting.

how to use iso settings in photography

“Streets Of NYC” captured by Björn Lexius (Click Image to See More From Björn Lexius)

I suspect this is because of the way it is being taught. You see, ISO started out as a property of film, and it was much easier to visualize it in terms of the old technology. So that’s where I want to start my explanation, before bringing you into the 21st century with ISO today.

ISO actually started out as ASA, which stands for American Standards Association. Decades ago, a commercial film manufacturer came up with a set of numbers to define the sensitivity of different types of film. That set of numbers was accepted by the American Standards Association, so all American manufacturers could use the same system. Later, the American standard was adopted by the International Standards Organization, so ASA became ISO.

What does all that mean? Well, it means that the letters ISO didn’t really stand for anything except for the name of an organization.

What is important is what ISO referred to, which was the sensitivity of the film. The emulsion on some films reacted quite slowly to light, and on other films much faster. Slower films had a smaller ISO number, like 25, 64, 100. Faster films had a higher number, like 200, 400, 800.

A slow film needed a relatively high level of light to create a well-exposed photo. That meant that to take a photo in darker conditions, you would need to use a fairly wide aperture and/or a fairly slow shutter speed to get a result. On the other hand, a faster film reacted to light a lot more quickly, so it needed much less exposure to light to take a photo.

Fast film sounds pretty good, doesn’t it? A chance to take a photo in any conditions without a tripod, and to freeze moving subjects with very fast shutter speeds. So why didn’t everyone just use fast films all the time?

iso settings in digital photography

Photo captured by Beebo Wallace (Click Image to See More From Beebo Wallace)

The answer is that the advantages of fast films came with a trade-off: loss of image quality. The grains of emulsion on a fast film were larger, so a photo taken on a film with ISO 400 or 800 had a rougher, ‘grainier’ look. This may not have been a problem in a small print, but became quite apparent with big enlargements. Consequently, most professional photographers preferred to use slower films of 100 or 64 ISO for most of their work.

So is this just a lesson in ancient history? After all, you have a digital camera, so what does all this have to do with you. Well, it may surprise you to know that despite the huge revolution in technology, the essentials of ISO have not changed one bit.

Your camera should allow you the option of adjusting your ISO setting. Just like in the days of film, if you set your ISO to a low number like 100, you will need more light to create a correct exposure. That means that you may need to keep a tripod handy for cloudy days, and in certain low-light situations you may not always get the aperture and shutter speed settings you want. If you set your ISO to 400 or 800, your camera will become much more sensitive to light; you will be able to shoot in exactly the same conditions without a tripod, and with greater flexibility to choose the aperture and shutter speeds you want.

But here is the amazing part. Higher ISO settings still come with the same trade-off that once existed with film. Along with the speedier sensitivity to light, you can also expect the image to have a grainier finish. I don’t know if it is pixelation or digital noise, or a combination of both, but it is generally understood that for all their advantages, high ISO photos come with a reduction of image quality that becomes more obvious the more you enlarge the image.

iso settings tips photography

“Man at the metro” captured by Six Pixels (Click Image to See More From Six Pixels)

So there you have a quick introduction to what ISO is all about. Perhaps I am just showing my age, but I find this subject easier to explain in old-technology terms. For many people it is easier to visualize when related to something solid like film, rather than something that happens on a computer chip. Anyway, I hope this helps you if you have had trouble understanding what ISO is all about.

About the Author:
Andrew Goodall writes for and is a nature photographer based in Australia. He manages a gallery in Montville full of landscape photography from throughout Australia.

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  1. Avangelist says:

    The result of using High ISO settings on the camera, is that the processor guestimates elements of the image being taken, this allows it to write the data faster.

    On some cameras, but less so as they release new models, this causes some adverse particles around the edges of objects which can look rather nasty. It can also mean you get colour spots in contrasty areas.

    I’ve gone from a D80 to a D300s in the last 6/7 months and the difference in high ISO quality is astonishing.

    It’s not really until you begin looking at an image at 100% you will even notice these things and for most, if not all, you wont tell the difference once it is actually on paper, or has been resized for web viewing.

  2. Avangelist, it has nothing to do with the processor guessing or write speed.

    On a digital camera it is simply the addition of electronic gain (amplification) to the fixed signal level that comes from the sensor. Think of the grain as being like the hiss you get on an audio amplifier when you turn the level up high, adding more gain. A higher ISO will have more hiss (noise).
    But there is more too it than just noise and grain with a digital camera. It also effects dynamic range and latitude. There will be an optimum “native” ISO for every camera where the maximum dynamic range is delivered. Adding or subtracting gain from the native ISO can reduce the latitude of the camera buy either cropping blacks if the ISO is too low or clipping whites if it is too high.

  3. Robyn says:

    Thanks for a great article Andrew! It might be in ‘old-technology’ terms but you’ve explained it all in a simple understanding way.

  4. Lisa says:

    Thank you for writing this. I am a hobby photographer. I have taken classes, read books, watched videos and still can not understand some of the settings on my camera and NEVER go out of auto mode because of it. It is because of my learning style and the fact that many of the settings do “not make sense” such as the term ISO not standing for anything other then the name.
    This was one of the few articles that helped clear some of it up. Believe me, if it was made clear to me, it should be clear to anybody!
    thanks again

  5. Kit says:

    Great article. However to side track the main content of the article let me clarify what ISO really is. 1. It stands for International Organization of Standardization. Not International Standards Organization. I know I’m splitting hairs. When ISO startled after World War II the organization based their name of the Greek word isos which means equal. All member nations regardless of size each have one vote on the standards that are introduced. They each have equal footing if you will. 2. Because their name would be different in each language they settled on ISO. So regardless of the language the short form of their name is ISO. Like the old film standard set by ASA and then adopted by ISO the digital ISO for sensor sensitivity is standardized as well from manufacturer to manufacturer. This benefits you and me the consumer. The Central Secretariat (headquarters) of ISO is in Geneva, Switzerland.

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