ISO: Film Speed

ISO is the film speed, meaning that is how fast the film or the camara lets in the light and how much it lets in a certain amount of time. For example, The first picture was used with just flash. Which drowns out the lights in the background. The 2nd is using an ISO of only 50. That means that it doesn't let as much light in for say, one second that the picture is being takin. This makes it really dark being there wasn't alot of light. Unlike the last picture that was taken with an ISO of 5000. As you can see it becomes a lot brighter because it lets in more like in that one second.

Some reasons you wouldn't want to use a high ISO is if your in a really well lite scenery, because it would make your picture way to white and bright. A good reason to use ISO over flash is if you want to see the lights in the picture of how they really are. Flash drowns out the light to much, as seen.