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EXPOSURE

A photograph's exposure determines how light or dark an image will appear when it's been captured by your camera. Believe it or not, this is determined by just three camera settings:aperture, ISO and shutter speed (the "exposure triangle"). Mastering their use is an essential part of developing an intuition for photography
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EXPOSURE TRIANGLE: APERTURE, ISO & SHUTTER SPEED

Each setting controls exposure differently:

Aperture: controls the area over which light can enter your camera
Shutter speed: controls the duration of the exposure
ISO speed: controls the sensitivity of your camera's sensor to a given amount of light

One can therefore use many combinations of the above three settings to achieve the same exposure. The key, however, is knowing which trade-offs to make, since each setting also influences other image properties. For example, aperture affects depth of field, shutter speed affects motion blur and ISO speed affects image noise.

The next few sections will describe how each setting is specified, what it looks like, and how a given camera exposure mode affects their combination.

APERTURE

Aperture controls the brightness of the image that passes through the lens and falls on the image sensor. It is expressed as an f-number (written as “f/” followed by a number), such as f/1.4, f/2, f/2.8, /f4, f/5.6, f/8, f/11, f/16, f/22, or f/32.

Changing the f-number changes the size of the aperture, changing the amount of light that passes through the lens. The higher the f-number, the smaller the aperture and the less light that passes through the lens; the lower the f-number, the larger the aperture and the more light that passes through the lens. For example, changing the aperture from f/4 to f/5.6 halves the amount of light passing through the lens and halves the brightness of the image that falls on the image sensor.

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SHUTTER SPEED

Shutter speed is a measurement of the time the shutter is open, shown in seconds or fractions of a second: 1 s, 1/2 s, 1/4 s … 1/250 s, 1/ 500 s, etc. The faster the shutter speed, the shorter the time the image sensor is exposed to light; the slower the shutter speed, the longer the time the image sensor is exposed to light.

If you are photographing a subject that is in motion, you will get different effects at different shutter speeds. Fast shutter speeds will “freeze” motion, while slow shutter speeds introduce blur from two sources

ISO

The ISO speed determines how sensitive the camera is to incoming light. Similar to shutter speed, it also correlates 1:1 with how much the exposure increases or decreases. However, unlike aperture and shutter speed, a lower ISO speed is almost always desirable, since higher ISO speeds dramatically increase image noise. As a result, ISO speed is usually only increased from its minimum value if the desired aperture and shutter speed aren't otherwise obtainable.
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18 July 2017
18 July 2017
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