Iris apertures are used to manually vary the intensity of light, and the angle of incidence, of a cone of light. An iris apertures consists of a number of metal blades called an iris. These are hinged and can increase or decrease the size of the hole between them. Iris diaphragms are used to control the aperture. Iris diaphragms function in the same manner as the pupil of a human eye functions to control the effective diameter of the lens opening. Control of aperture is easily accomplished by means of a variable diameter iris diaphragm. An iris shutter creates a variable iris aperture which ranges from completely closed to completely open. There are many types of irises on lenses. Examples include manual iris control and automatic iris control. A lens is said to be at full aperture when iris apertures do not obstruct the path of light through the lens.

To use iris apertures either the depth of field or the light levels available should be determined. Iris diaphragms control the effective diameter of the lens opening by reducing the aperture size and increasing the depth of field. Continuously variable iris diaphragms are designed to provide smooth operation over many thousands of cycles. Zero aperture iris diaphragms can provide total light extinction. Such iris diaphragms are often used in systems where the dark signal must be measured. Typically in iris apertures the number of blades ranges from 5 to 20. Iris apertures are usually measured in f-numbers. A typical standard lens will have an f-stop range from f/16 (small aperture) to f/2 (large aperture). Zoom lenses typically go from f/2.8 to f/6.3. The reason for consumer zooms to have a variable iris aperture is that more light is needed as the focal length increases. The aperture is calculated by dividing the focal length by the diameter of the actual diaphragm. The sharpest results for most lenses are found at two or three stops down from their maximum iris apertures.

Iris apertures are used to manually vary the intensity of light, and the angle of incidence, of a cone of light. An iris apertures consists of a number of metal blades called an iris. These are hinged and can increase or decrease the size of the hole between them. Iris diaphragms are used to control the aperture. Iris diaphragms function in the same manner as the pupil of a human eye functions to control the effective diameter of the lens opening. Control of aperture is easily accomplished by means of a variable diameter iris diaphragm. An iris shutter creates a variable iris aperture which ranges from completely closed to completely open. There are many types of irises on lenses. Examples include manual iris control and automatic iris control. A lens is said to be at full aperture when iris apertures do not obstruct the path of light through the lens.

To use iris apertures either the depth of field or the light levels available should be determined. Iris diaphragms control the effective diameter of the lens opening by reducing the aperture size and increasing the depth of field. Continuously variable iris diaphragms are designed to provide smooth operation over many thousands of cycles. Zero aperture iris diaphragms can provide total light extinction. Such iris diaphragms are often used in systems where the dark signal must be measured. Typically in iris apertures the number of blades ranges from 5 to 20. Iris apertures are usually measured in f-numbers. A typical standard lens will have an f-stop range from f/16 (small aperture) to f/2 (large aperture). Zoom lenses typically go from f/2.8 to f/6.3. The reason for consumer zooms to have a variable iris aperture is that more light is needed as the focal length increases. The aperture is calculated by dividing the focal length by the diameter of the actual diaphragm. The sharpest results for most lenses are found at two or three stops down from their maximum iris apertures.

Iris apertures are used in many applications. Iris apertures are commonly used to decrease the intensity in front of a photo detector, or to force a laser to operate in a single transverse mode when applied inside an optical resonator. Iris apertures are most commonly used for photography purposes in cameras such as zoom cameras, network cameras, and SLR cameras. Iris apertures can also be used in projectors and guns.