Aperture, Iris and Exposure

Camera iris—the hole in the middle is the aperture.

People often get confused between iris, aperture, exposure and other related photographic terms.

Here are the differences in a nutshell:

• The iris is the part of the camera that has an adjustable opening to allow light to enter and fall upon the image plane (i.e. the sensor CCD, film, etc).
• The aperture is the size of the opening in the iris.
• Exposure is the amount of light falling upon the sensor.

Although the iris/aperture is the primary method of controlling exposure, there are a number of addition methods, including:

• Shutter
• ISO
• Filters (e.g. neutral density filter)
• Gain