ISO is the camera’s sensitivity to light and controls the image quality. ISO used to be a numerical standard describing a roll of film’s sensitivity to light, making images darker or brighter depending on the degree of sensitivity. Since film is not used in digital cameras, the modern ISO setting represents how bright the final photo should be. Functionally, it operates the same way as film ISO did, increasing or decreasing the brightness of a photo. Low ISO numbers represent lower sensitivity to light, producing darker images, while high ISO numbers represent a higher sensitivity to light, producing brighter images. Higher ISO speeds should be used with caution as higher ISO produces more grain (also called noise).
For clear, high-quality photos, the lower the ISO number, the better. As a general rule, if the photo is too dark, try to stick to an ISO between 100 and 800 and tweak your shutter speed and aperture settings instead to increase exposure.
Noise is discolored pixels and lost detail that gives photos a grainy look. Every photo has a little noise, but too much noise is when the tiny imperfections overwhelm the photo and distract from the subject.
Look at the difference between these two photos. They were taken under the exact same conditions, but can you guess which one had the higher ISO?
I used an ISO of 500 for the photo on the left and an ISO of 8000 for the photo on the right. The additional noise is especially noticeable in the background area of the photo since it’s mostly a solid color.
Noise doesn’t have to be a bad thing. For example, the below examples are the previous photos at their original size. The pixels are less visible at this zoom, so don’t be afraid of higher ISO, just be aware of how they will impact your photo. Determine the level of noise you are comfortable with and don’t exceed that ISO. In just a moment, I will discuss how to cap your ISO when using Auto ISO. But first, when would you want noise?
There is a big debate on whether we should hate grain or embrace it. The best thing about photography is a good photo is one you like, so if you like it use it!
If you are in a low light setting or need a faster shutter speed, a higher ISO may be your only option. If having some grain is the alternative to missing the photo entirely, then it’s worth accepting. I shot the below photo with the ISO set at 3200. Carlsbad Caverns are dimly lit and don’t allow tripods. There is a limit to how slow handheld shutter speed can be without causing blur, so my only option was to increase the ISO.
Photos should tell a story and the story can go beyond the subject. Noise can create a dark and dreary mood for rainy days or photos expressing sadness.
It’s intimidating to think about and manipulate exposure settings with each capture. That’s why Auto ISO is an amazing tool! The camera will determine the ideal ISO based on the aperture and shutter speed. The risk with auto ISO is that the camera could select too high of an ISO and make an otherwise great photo unusable. The easiest solution to this is to cap the auto ISO settings, assuming your camera has the feature. Determine the highest ISO you can tolerate and set that number as the maximum. This will force you to think more about your aperture and shutter speed, but you won’t get photos with too much grain. You can always switch to manual ISO to override the cap if a particular shot calls for a higher ISO.
To access the auto ISO settings the Canon 6D:
I spent a long time intimated by ISO. But, at its core, it’s really very simple as long as you can remember these basics: