ISO can really affect night-time photography.

Here are two examples of the same shot with different ISO settings. Click on each photograph to open a larger version in a new window. The effects of high ISO are much more noticeable.

ISO 6400

You’ll quickly notice the graininess of the photo. This is because of the high ISO setting.

ISO 560

You’ll immediately notice how this shot does not have much grain in it at all.

In general, the lower the ISO the higher quality the photograph will be.