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What is ISO in photography and how does it work?

ISO in analog photography or film measures the camera sensor's sensitivity to light. ISO in digital photography are values to tell your camera how bright the output image should be, given a particular exposure. Basically, it brightens the photo you already captured and this process takes place inside the camera. In the days of analog photography, you had to change your roll of film to use a different ISO. With digital cameras, we have the advantage of being able to control the ISO of every single shot.

The ISO is displayed as a number (100, 200, 400, 800) and can help you photograph in darker environments. By increasing the ISO number, the photo will be increasingly brighter, but raising your ISO has consequences to the grain level (also known as noise) and the dynamic range, which is the difference between the darkest and lightest tones in a photo. The lower the ISO number, the less sensitive your camera is to light, and the finer the grain and vice versa.

What does ISO stand for in photography?

ISO represents the “International Organization for Standardization”, an International Organization for Standardization that develops standards to ensure quality, safety, and efficiency of products, systems, and services. However, the camera ISO does not directly refer to this organization. From the moment the two film standards 'ASA' and 'DIN' were combined into one new ISO standard, it was referred to as 'ISO'.

ISO and the Exposure Triangle

ISO is one of the three pillars of the Exposure Triangle; the settings that give you control over the exposure and brightness of an image. The other two pillars are the Aperture and Shutter Speed

With aperture, you get a shallower depth of field as you widen the aperture (low f-number) to let in more light. As the exposure time (shutter speed) increases to let in more light, it becomes harder to get sharp images of moving objects.  

Although ISO is part of the Exposure Triangle it isn't part of the exposure of an image, because, it does not change the amount of light that reaches the camera sensor as Shutter Speed and Aperture do. In essence, it brightens the photo you already captured. ISO has been introduced to control brightness independently from the aperture and the shutter speed to create a correct exposure under all circumstances. For example, when photographing in darker areas. However, if you increase your ISO, your images get noisier and will show more grain. The amount of noise that corresponds to the ISO values varies per camera.

If you understand the exposure triangle and the relationship between these three elements, you will gain more control of the images you want to capture.

What are the different ISO stops on a camera?

Usually, the value ISO starts with, is ISO 100. This is the lowest ISO and also called the base ISO. With the base ISO, you are able to produce the highest image quality and minimize grain or noise as much as possible. The maximum ISO depends on which camera you use and it can get up to ISO 25600 and in the latest digital cameras even higher. However, your image quality will reduce a lot with such high ISO settings. 

ISO Chart

The most common ISO stops or ISO values on a camera are the following:

  • ISO 100 
  • ISO 200 (twice as bright as ISO 100)
  • ISO 400 (twice as bright as ISO 200 and 4 times as ISO 100)
  • ISO 800 (twice as bright as ISO 400 and 8 times as ISO 100)
  • ISO 1600 (twice as bright as ISO 800 and 16 times as ISO 100)
  • ISO 3200 (twice as bright as ISO 1600 and 32 times as ISO 100)
  • ISO 6400 (twice as bright as ISO 3200 and 64 times as ISO 100)

Most cameras offer more ISO values then the full ISO stops mentioned above. This is, for example, the series of ISO stops my camera offers:

100 - 125 - 160 - 200 - 250 - 320 - 400 etc. and it goes up to a maximum of X ISO.

Apart from full stops, I can also choose from 1/3 stops.

How to use ISO and when to change your ISO settings?

My advice is to only increase your ISO when you are unable to brighten the photo via the other two pillars of the exposure triangle: the shutter speed or aperture. Adjusting your ISO determines how the camera deals with the amount of light after the exposure is done. The less light you capture, the lower the quality of your image.  

So, if you can, try to use the lowest ISO to achieve the highest image quality. 

Low ISO number > Lower sensitivity > less noise/grain > higher quality images

When this isn't possible, for example when photographing in darker areas, then slightly increase your ISO to brighten the image. 

To be able to change the ISO, you need to set your camera to manual, or one of the semi-automatic modes (S/Tv, A/Av, P). If you are still learning photography, you can also switch ISO to auto-mode (or 'A' mode) so that the camera will choose the ISO for you. But be aware of the effect a certain ISO has on your photos. Automatic mode doesn't always choose the perfect settings.

Where to find the ISO on a camera?

Depending on the model of your camera, there are different ways of adjusting ISO. On most DSLR's you can find the ISO on the LCD screen of the camera and also in your viewfinder. On more professional cameras there's a separate button for ISO to get quick access to adjust the ISO. On other cameras, you can usually find the ISO in the menu. If you can't find it, my best advice is to check your camera manual. Even the latest cameras on smartphones like the iPhone have an ISO option.

ISO on a camera

I hope this article was helpful to understand ISO in photography and how it works. You could help me in return by sharing this article on the world wide web. I appreciate every share on Facebook or pin on Pinterest. From the moment you no longer have to think about all the photography basics, it gets really fun to go out and capture all the beauty of our planet.