What is Shutter Speed?
Shutter speed is the length of time camera shutter is open, exposing light onto the camera sensor.
What is a Fast Shutter Speed?
A fast shutter speed is often referred to the shutter speed that is fast enough to freeze action or moment. Typically, photographers refer to small fractions of a second, such as 1/250th of a second or faster when talking about fast shutter speed.
What is a Long Exposure?
Shutter Speed Chart
What is ISO?
The ISO refers to how sensitive the digital sensor in your camera is to light. The lower the ISO number, the less sensitive it is to light. Setting a higher ISO number increases the sensitivity of your camera sensor to light. Most cameras have ISOs ranging from about 50 or 100 ISO right up to 16,000 ISO or higher.
Higher numbers mean your sensor becomes more sensitive to light which allows you to use your camera in darker situations. The cost of doing so is more grain (although cameras are improving all the time and today many are able to use high ISO settings and still get very usable images).
An example of a situation you might want to choose a higher ISO would be photographing an indoor sporting event where the light is low and your subject is moving fast. By choosing a higher ISO you can use a faster shutter speed to freeze the movement perfectly.