What is it?
It is an international standard for measuring the sensitivity of light of film. But we now mostly don’t use film. So how does it relate to your digital camera? Why do you need to know about it?
Digital cameras may not use film, but the sensor recording the image uses the same sensitivity scale outlined by the ISO standard.
In film days, ISO 100 film was used outdoors where there was lot of light. 400 film was used in the shade and 800 was used indoors with flash.
Most modern digital cameras, have a range of ISO from 100 to 1600 as a minimum, with some cameras boasting much higher.
How do I use it on my camera?
Depending on the make and model of your camera, you may have a dedicated button for changing it, or you may have to change it through the menu system. Most of the latest cameras will have an intelligent Auto ISO that allows you to set a minimum and maximum value.
What does it do to my pictures?
The short answer to this question is, not a lot! By increasing the it when taking your picture it will allow you to take a picture in a darker environment. So as a general rule always use ISO 100. If you cannot take the picture at 100, then change it. As the light around you gets darker, you will need to increase your ISO to match.
Technology has made ISO nowadays just a number, gone are the days that 1600 was “noisy” and you lost detail in your pictures when using it. The new Canon 700D allows you to use ISO 6400! That film speed even 5 years ago was considered unusable.
Examples
The picture above was taken in 2007 on a then new Canon 30D, the picture settings were Aperture F5.6 Shutter Speed 1.6 seconds and ISO 1250, the image to the left has been processed to look like it was taken on a 1000D at the same ISO, with newer technology that has better ISO, there is less noise.
This picture was taken at 3200 at about 9.30 at night, the high number allowed me to take this picture where the only light available was moonlight. The Aperture was F2.8 and the shutter speed was 1/60th.
This shot is a crop of the original shot to show the noise that was around with older cameras, this was taken on a Canon 300D, the settings were Aperture F3.5 Shutter speed 1/160th and ISO 1600, you can see the grain mostly in the darker areas of the image.
I have reprocessed this image and reduced the noise but there is still a little evident. Newer cameras will do this for you in camera without the need for reprocessing.
This image was taken in such a dark setting that the camera needed a torch to focus! The settings were Shutter speed 1/10th Aperture F4 and ISO 1600, the settings were used to bring out the background that was extremely dark, the couple were lit by two flashes.
Try This
Set your camera to Manual mode. Set your camera to Aperture F16 and Shutter speed 1/100 and ISO 100, take a picture, then change the ISO to 200 and take the same picture, then repeat for 400, 800 and 1600, what is happening to your pictures? What else is changing?
Have a read about Shutter Speed and Aperture.