ISO in Digital Photography Explained – A Beginners Guide

Mastering ISO in digital photography is one of the cornerstones to stepping into manual mode and taking good photographs!

There are 3 key elements to what is referred to as the “Exposure Triangle”, namely, shutter speed, aperture and of course ISO. Changes in any one of these 3 settings on your camera will usually necessitate changes in one or both of the other settings.

Exposure Triangle

Exposure Triangle

The Basics Of ISO in Digital Photography

Lets start with the basics and essentials of this topic. ISO in digital photography is an indicator of the sensitivity to available light of your camera. The component in the camera that does this is the image sensor, or just “sensor”.

When you get down to the nuts and bolts of it, the lower the ISO setting, the less sensitive your camera is to light and the finer the grain aspect of your image. In other words, the image will be sharper. Conversely, the higher the ISO setting, the more sensitive your camera will be to light. The resulting image will have a more grainy appearance or appear to be less sharp. The grainy aspect of an image is often referred to as “noise” in the image.

Compare the images below to see the difference ISO settings make.

As you can see from the images above, the image taken with an ISO setting of 200 is sharper and less grainy than the image taken with ISO setting on 1600

You would usually use higher ISO settings in darker situations, with fast shutter speeds. An example of this would be an indoor sporting event. In this case, you would want to freeze the action, but having to compensate for the lower light. But use with caution – the higher the ISO you select, the noisier the image will be.

The generally accepted normal setting is ISO 100 which will give you great, sharp images with very little noise.

I hear you all say at this point, “But why can’t I leave the ISO setting on auto and let the camera handle this for me?”

There are problems with using auto ISO mode. The camera automatically chooses the shutter speed and aperture settings for the shot. For example if you manually changed your ISO setting from 100 to 400, you would find that you can shoot in lower light at higher shutter speeds and (or) smaller aperture settings, to get the desired effect for your shot.

Selfie Stick

How Do You Choose The Right ISO?

There are a few things you need to bear in mind when choosing an ISO setting:

  • Lighting – is the subject well lit?
  • Noise – do you want a shot that is grainy or sharp?
  • Stability – will you be using a tripod?
  • Motion – is the subject stationary or moving

Some rules of thumb you can use when deciding on ISO settings are as follows:

  • If light conditions are good, you don’t want a grainy shot, you are using a tripod and the subject is not moving, use a low ISO setting.
  • If the light is not good, you want noise, not using a tripod, or the subject is moving you can increase the ISO to enable shooting with a faster shutter speed and get good exposure on the image

Some situations where you may consider a higher ISO

  • Candle lit scenarios
  • No flash locations – concerts, art galleries (some art galleries do not allow flash photography)
  • Indoor events with fast moving subjects – eg. Indoor sports events

You can use the Quick Reference chart below to start experimenting with ISO in conjunction with shutter speeds and aperture.

ISO in digital photography

Here is another graphical representation of ISO that may help you to get to grips with the concept.
These are guidelines for you to experiment with. When start shooting with different ISO settings, use the indicated ISO setting as the starting point, but shoot the same image with different ISO settings and then compare the results.
You will quickly get a feel for the right setting to use in certain light conditions.


Understanding ISO in digital photography is essential to your growth as a photographer and taking better shots that will be properly exposed in all light conditions. You cannot, however change ISO settings in isolation. It is important to understand the inter-relationship between ISO, Aperture and Shutter speed. You can read more about this in my post on the Exposure Triangle.
These settings may seem a bit daunting at first, but the results are well worth the effort!



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