Exposure

Exposure is the amount of light received by a camera’s recording medium during image capture. It is controlled chiefly by aperture, shutter time, and sensor or film sensitivity.

Aperture: Aperture is the adjustable opening in a lens that admits light to a camera. Changing aperture alters the light reaching the recording medium and the depth of field.
Exposure triangle: The exposure triangle is a teaching model linking aperture, shutter speed, and ISO sensitivity. It summarizes the three main controls photographers balance to set exposure.
Overexposure: Overexposure occurs when excessive light produces image tones brighter than intended, sometimes losing highlight detail. It is the too-bright failure mode of exposure control.
Reflective metering: Reflective metering estimates exposure by measuring light reflected from the scene toward the camera. Most built-in camera meters use this approach to recommend exposure settings.
Shutter speed: Shutter speed is the duration a camera’s shutter exposes its recording medium to light. Longer exposure time admits more light, while shorter time can freeze motion.
Depth of field: Depth of field is the range of distances in an image that appear acceptably sharp. Aperture changes exposure while also changing the image’s apparent zone of focus.
Underexposure: Underexposure occurs when insufficient light produces image tones darker than intended, sometimes obscuring shadow detail. It is the too-dark failure mode of exposure control.
Incident light metering: Incident light metering measures illumination falling on a subject rather than light reflected from it. It avoids the subject-reflectance assumptions that can mislead reflective exposure readings.
ISO speed: ISO speed is a standardized measure of a camera system’s sensitivity to light. Raising ISO permits brighter output at a given light level, usually with more image noise.
Motion blur: Motion blur is the streaking or smearing of moving subjects or camera movement during image capture. Longer shutter times increase the chance that movement will register as blur.

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