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Exposure plays an important role in photography. And it is also one of the first problems that photography beginners will encounter. Here we will provide guide to exposure in photography. 


Explanation of Exposure
In photography, exposure is the amount of light per unit area (the image plane illuminance multiolies the exposure time) reaching a frame of photographic film or the surface of an electronic image sensor, as determined by shutter speed, lens aperture, and scene luminance. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region. In a word, the exposure refers to the brightness of the picture during shooting.

Factors that Affect Exposure
1. Aperture
The aperture is the diaphragm hole where light travels through the lens. It regulates the amount of light that goes through your lens to the camera’s sensor. The aperture setting on a lens is expressed in “f-stops”, the ratio of focal length to effective aperture diameter. The smaller the number, the bigger the aperture. For example, the f4 aperture is much larger than f16 aperture.



2. Shutter Speed
In the case of a fixed aperture, the time that the light stays inside the camera is also an important factor affecting the exposure. And the device that controls the time the light stays inside the camera is called the "Shutter". Shutter speed (or exposure time) is the length of time when the film or digital sensor inside the camera is exposed to light, for example, 1/60s, 1/80s, 1/120s, 1/1000s. The shutter time is inversely proportional to the shutter speed. The slower the shutter speed, the more light comes in, and the brighter the photo. If the shutter speed is very long, the moving objects in the photo will become very blurred along the direction of their motion trajectory, for example to highlight the sense of speed in a car. But landscape photographers will use slow shutter speed to highlight the dynamics of rivers and waterfalls.



3. ISO
In addition to the aperture and shutter, the sensitivity of the light-sensing element in the camera, also known as the ISO, is also another factor that affects exposure. The higher the ISO, the sensor will seem to have captured more light. The photo will be brighter. However, it’s not referring to the amount of light it captures, but to the amplification of the signal from the light itself. Therefore, when the signal is amplified too much (too high ISO), noise appears in the photo.



Therefore, the aperture, shutter, and ISO are usually called "three elements of exposure. In order to have normal exposure during shooting, a combination of these three exposure elements is necessary. When the sensitivity (ISO) is fixed, increase the aperture and the amount of light entering the camera, meanwhile you must also increase the shutter speed to shorten the time the light stays inside the camera; if you reduce the aperture and the amount of light entering the camera, in order to ensure normal exposure, you need to slow down the shutter speed to extend the time the light stays inside the camera.

Application of Long Exposure
Although for a variety of different shooting environments, through different combinations of the three elements, the picture can be exposed to normal, but the quality of each photo may also be different. Long exposure is a unique method to create clear and artistic photos. Long-exposure or slow-shutter photography refers to using a long-duration shutter speed to sharply capture the stationary elements of images while blurring, smearing, or obscuring the moving elements, such as satin-like water currents, traffic flow at night, etc. In addition, if you use a small aperture and a lower ISO setting, the photos will not only be clear, but the colors will be bright and colorful. You can also use some photo props such as Backdrops to make your photos more artistic, especially  to create beautiful night photography.



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