shutter speed and aperture

Shutter speed

In  cameras, the  shutter speed is the time that the shutter is open when taking a photograph. Along with the aperture of the lens, it determines the amount of light that reaches the film or sensor the exposure is measured in units of exposure, sometimes called stops, representing a halving or doubling of the exposure.

In addition to its effect on exposure, the shutter speed changes the way movement looks in the picture. Very short shutter speeds can be used to freeze fast-moving subjects, for example at sporting events. Very long shutter speeds are used to intentionally blur a moving subject for artistic effect. Short exposure times are sometimes called "fast", and long exposure times "slow"Adjustment to the aperture controls the depth of field, the distance range over which objects are acceptably sharp; such adjustments need to be compensated by changes in the shutter speed.

Aperture
An aperture is a hole or an opening where light travels. The aperture determines how light the admitted rays are which is of great importance for the appearance at the image plane. If an aperture is small, then highly light rays are admitted meaning the focus at the image plane. If an aperture is wide, then dark rays are admitted, resulting in a sharp focus only for rays with a certain focal length. This means that a wide aperture results in an image that is sharp around what the lens is focusing on and blurred if not. The aperture also shows how many of the incoming light is actually admitted and thus how much light reaches the image plane (the narrower the aperture, the darker the image for a given exposure time).