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What is ISO? A camera’s sensitivity to light explained, and how to use it

If you’re relatively new to digital photography, making sense of all the lingo and acronyms can be a rather daunting task, but it’s also key to knowing your way around your camera and taking excellent photos. One of the most confusing settings on your shooter is undoubtedly ISO, so we’ve put together this dead-simple explanation to help you master it in just a few minutes. Here’s what you need to know.

First, let’s break down the acronym. ISO is short for International Standards Organization – the main governing body that standardizes sensitivity ratings for camera sensors. It’s a a term that was carried over from film. When you change your ISO setting, you’re adjusting your camera’s sensitivity to light. ISO settings can be anywhere from 24 to 6,400 (or higher), and these numbers have a direct relationship with the device’s sensitivity, so a lower setting makes it less sensitive and a high setting makes it more so. Along with shutter speed and aperture, ISO is one of the three factors that determine your picture’s exposure. Finding the right balance between these three settings is key to getting the perfect shot.

Finding the right ISO setting

First of all, you should know that a higher ISO typically translates to a noisy or “grainy” image, so as a general rule you want to use the lowest setting possible for your photos. Check out the picture below to see the difference it can make. 

ISO difference

A lower ISO will usually produce more color-accurate, aesthetically pleasing images, but there are situations where a higher ISO is desirable. The proper ISO setting really depends on the level of lighting you’re shooting in and the visual effect you’re going for, so rather than relying on one over-arching rule, consult this list of tips:

  • If your subject is moving and you’re trying freeze the motion for a still, you’ll likely need a higher ISO setting to compensate for the high shutter speed and ensure your image gets enough light
  • If you’re going for more of a vintage aesthetic and want to add a little bit of grain to your photos, don’t be afraid to bump up the ISO a few notches
  • If you’re using a tripod to stabilize your camera you can usually get away with a slower shutter speed, which in turn allows you to use a lower ISO 
  • If you’re shooting an image that doesn’t require a large depth-of-field, you can increase the camera’s aperture (thus allowing more light into the lens) and use a lower ISO
  • If you’re shooting with artificial light (i.e., using a flash) you can typically get away with a lower ISO setting

You’ll probably need to experiment a bit until you hit the sweet spot, but while you tinker with settings, keep the following in mind: 

  • Never trust your camera’s display. Don’t assume that your picture will turn out just because the tiny 2-inch preview looks adequate. Your shots almost always look different on your computer, and you probably won’t be able to spot noise on your camera’s small, low-resolution display. For this reason, we highly recommend that you zoom in a bit to check your images for grain. There’s nothing worse than taking a bunch of seemingly great shots only to discover they’re noisy and speckled when you upload them to your PC.

Still confused by ISO? Feel free to leave your questions in the comments below and we’ll see if we can help you out! 

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