What does ISO do? ISO refers to the cameras’ sensitivity to light. While shutter speed determines how much light comes, ISO refers to how much of that light is captured by the camera.

Tradeoff – Grainy Images: High ISO’s like 3200 or 6400 or way higher like 25,000+ give you lot more light but will give you grainy images.

When to use a low or high ISO?

For clear images, use a low ISO. For most purposes, you don’t need to tweak ISO…just leave it at the lowest setting and you’ll be fine.  So for basic shots indoors or product photos in a studio, etc, you can set it to the lowest and forget about it.

Most people don’t want grainy images. So why should you use high ISO’s? Because in certain low light conditions like shooting at night with no light around you, a high ISO is probably the only way to get a usable image.

Shutter speed v. ISO

If you want a clear image in a dim light environment, shoot at the slowest shutter speed you can to get the most light in. If that isn’t enough, then increase ISO. A high ISO is used when your shutter speed isn’t giving you enough light. For example, let’s say you want to shoot at a specific aperture and shutter speed. If your image is still dark, your next option is to increase ISO.

When shutter speed is too slow, you ma capture movement that you don’t want. So you need to balance that with the ISO setting. So instead of a 1 sec shutter speed at ISO 100, you can do a 1/2 sec shutter speed with 400 ISO. It’s a trial and error process. But with practice, you’ll know what works in different situations.

Example of Low v. High ISO – Three Images shot under the same dim lighting.

  • The first image below was shot at ISO 100. Though low ISO’s mean your image will be clear and sharp, here it is so dark that you can’t even see the box in the image.
  • The second image was taken at ISO 3200. You can see how much more light there is – note that it’s the same lighting, same aperture and shutter speed.
  • The third image is also shot at the low 100 ISO but the shutter speed was slowed down to be close to 1 second. The second and third image look similar but the extra light was achieved in different ways – one with a higher ISO and the other with a slower shutter speed.
  • It may not be apparent in these images but the ISO 3200 image (when zoomed in) would be grainier than image 3 (slow shutter speed with ISO 100). So always start by tweaking shutter speed. If there is so little light that ISO is the only option, then increase ISO.

iso example blog

Hope this post helped understand ISO better. Do you use ISO settings differently? Tell us how.