Here we can see the difference that changing the ISO on your camera can make. ISO on a digital SLR refers to the amount of light that the sensor is exposed to.

In the case of these images they were all taken at the same exposure level of -1/3 of a stop with different shutter speeds to maintain that same level of exposure.

Each image was shot on the Canon EOS 700D with a Canon 100mm f2.8L Macro IS USM Lens. Each image was also shot with the lens wide open at f2.8

You can see with each image that as the ISO number increases the more grain becomes visible on the image reducing the overall quality of the final image. Below I’ve listed the recipe for each image in order to get the exposure.

You can also see a pattern form with the shutter speed as the ISO goes up a full stop the shutter speed is halved.