how fast the shutter speed oipens and closes to let light into the camera
aperture
how big the opening of the lens is to let light in
shutter speed is usually expressed in fractions of a second
1/250th of a second is fast
1/30th of a second is slow
anything slower than 1/30th of a second MUST! use a tripod
aperture is usually expressed in f numbers
f/2.1 is large
f/22 is small
