Today’s post introduces the final corner of the exposure triangle, ISO.
In traditional film photography, ISO is the measure of the film’s sensitivity to light, in digital photography ISO refers to the sensitivity of the sensor.
The higher the number, the more sensitive the sensor is to light. Higher ISO settings are traditionally used in darker settings, the pay off with this higher sensitivity though is that images get grainier the higher you push the ISO.
ISO 3200 | ISO 200
In the two pictures above you can see that the photo on the left is far grainier when viewed at 100% than the shot on the right. This is down to the ISO being so much higher in the first photo.
Different cameras will produce different levels of grain at the same settings. My Canon 50d DSLR is awful for producing grainy photos at low ISO settings, whereas my Fuji X100S handles low light much better and produces ‘quieter’ images at the same ISO setting.
The lowest ISO your camera provides is called your base ISO, using this will produce crisp, clean images of the highest quality.
The important thing to remember is that each step between the numbers doubles the sensors sensitivity. So ISO 400 is two times more sensitive than ISO 200, which in turn is two times as sensitive as ISO 100.
Stepping up your ISO from 100 to 400 will allow you to shoot at higher shutter speeds and with a smaller aperture.
For example if an image took a second to capture at ISO 100, changing the ISO to 800 would allow you to take the photo at 1/8 of a second. This is a massive difference when it comes to photographing children or any other moving subject!
I rarely use flash so always try and shoot at the lowest ISO possible to keep grain to a minimum, I only bump up my ISO when there isn’t enough light for me to capture an image clearly with the light available, and then, only as far as I need to go.
1) The sensor sensitivity doubles with each step up in number
2) The higher your ISO, the grainer your image will be
So there you have it, the three corners of the exposure triangle explained. When you understand how the three of these work together it makes moving to manual so much easier.