Adjustable sensitivity of the sensor medium isn’t a new thing. It’s been around since the days when film was the standard format. But these days it’s a lot easier than it used to be, film required you to change the roll to adjust the ISO. These days it’s much easier to change ISO with digital. Today, it’s just a button.
So, you’re wondering what ISO is? basically the ISO speed determines how sensitive the camera’s sensor is to the light coming through the lens. This means that if you set the ISO to a lower number, the sensor will be less sensitive to the light. Consequently, if you set the ISO to a higher number it will be more sensitive.
Many people at first will think “hooray! all our problems are solved! No more dark photos!!” this is true. BUT, there are some drawbacks when taking a photo at higher ISO’s.
Despite which format you use, both film and digital suffer from the same drawbacks. Noise. Wait, how can an image have noise? Well it doesn’t mean sound, it means grain and blemeshes created by the sensor medium.
When you boost the ISO up very high you will see a degraded image quality. With modern day digital and photo editing software there are some very good noise removal tools that can actually remove noise completely.
Here I will show you some examples. First, we have an image taken at ISO 3200 (Canon EOS 10D):
And now we have an image taken at ISO 100 with the same camera:
The Best Usage
The best way to use ISO is to aim to keep it as low as possible while still keeping the exposure correct. This way you will have less problems with noise. Take your time to experiment with it so you can understand the effects of ISO on your pictures.
If you have cheaper/slow lenses you will appreciate the higher ISO’s when shooting indoors.