photography Photography is the visual arts, art, application, and practice of creating images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is empl ...

, stopping down refers to increasing the numerical f-stop number (for example, going from 2 to 4), which decreases the size (diameter) of the aperture of a lens, resulting in reducing the amount of light entering the iris of a

lens A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...

. Reducing the aperture size increases the

depth of field The depth of field (DOF) is the distance between the nearest and the farthest objects that are in acceptably sharp focus (optics), focus in an image captured with a camera. See also the closely related depth of focus. Factors affecting depth ...

of the image. In the case of

film A film, also known as a movie or motion picture, is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, emotions, or atmosphere through the use of moving images that are generally, sinc ...

cameras, this allows less light to reach the film plane – to achieve the same exposure after stopping down, it is necessary to compensate for the reduced light by either increasing the exposure time, or using a

photographic film Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin photographic emulsion, emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the ...

with a higher film speed (ISO). In the case of

digital camera A digital camera, also called a digicam, is a camera that captures photographs in Digital data storage, digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film or film stock. Dig ...

s, stopping down the aperture allows less light to reach the

image sensor An image sensor or imager is a sensor that detects and conveys information used to form an image. It does so by converting the variable attenuation of light waves (as they refraction, pass through or reflection (physics), reflect off objects) into s ...

– to achieve the same exposure, it is necessary to compensate for the reduced light by either increasing the exposure time, or increasing the signal gain of the sensor by increasing the camera's

ISO The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries. Me ...

setting. Alternatively, more light can be added to the scene by increasing the amount of light illuminating the scene, such as by using or increasing the strength of electronic flash or other light sources. As a lens is stopped down from its maximum (widest) aperture, most lens aberrations ( spherical aberration,

coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to Nociception, respond normally to Pain, painful stimuli, light, or sound, lacks a normal Circadian rhythm, sleep-wake cycle and does not initiate ...

and astigmatism) are decreased, but lens

diffraction Diffraction is the deviation of waves from straight-line propagation without any change in their energy due to an obstacle or through an aperture. The diffracting object or aperture effectively becomes a secondary source of the Wave propagation ...

increases. The effect is that for most lenses, the balance between the decreasing aberrations and the increasing diffraction effects of stopping down the lens means that lenses have an optimum aperture for best results, often about three stops closed down from maximum aperture, so for a lens with a maximum aperture of ƒ/2.8, ƒ/8 would be the optimum aperture.

References

Photographic techniques {{Photo-stub