SimCam: Film and Digital Camera Simulator
Basic Exposure - Shutter and Aperture
All cameras have at least two ways to control light: the shutter and aperture. The aperture is like an iris in the eye, and controls light by changing size. When photographer takes a picture, the shutter opens briefly and the image is exposed.

In any shooting situation there are several combinations of shutter and aperture that could be considered correct. Which settings to choose is a matter of personal taste, and is usually influenced by how much light is available.

SimCam - Shutter and Aperture
original scene:
(as it might appear to the eye)
First set the camera to 1/500 at f/2.8 and take a shot. Then take another shot after changing the exposure to 1/60 at f/8. Notice how the overall brightness did not change.

In the second exposure you gave 3 stops MORE light with the shutter, but balanced it out by removing three stops of light with the aperture.

Remember that shutter speed, f-stop settings, and even film speed are all rated in units of "stops".

camera settings:
Shutter: Aperture:
final exposure: