Get to grips with the exposure triangle and discover how a digital camera captures an image with this simple explanation from Digital Photographer magazine‘s Matt Bennet…
Photography is all about capturing light, but precisely how we arrive at the correct or desired exposure is achieved through the careful balance of three main variables. These variables are ISO, shutter speed and aperture.
The first of these, ISO, dictates how sensitive your camera’s sensor is to the light. By increasing the ISO sensitivity of your sensor, your camera will be able to compensate for a lack of light. So, if you are in a dimly lit room, perhaps with just a small amount of light from a window to work with, using an ISO of 800, 1600 or even higher will mean that you can carry on photographing. However, there’s a price to be paid for this, and that price is noise. This is essentially a speckling that makes your photos look less smooth and clean. At lower ISO sensitivities, noise will be minimal, but will gradually increase as you raise the ISO sensitivity. However, modern cameras are far better than their predecessors at providing images with little noise at higher ISO values.
The second variable is shutter speed. This simply means the length of time that the camera’s shutter curtains remain open for when you press the camera’s shutter button. Unlike the ISO sensitivity, the shutter speed will have a profound impact on the images you capture. A fast shutter speed, for example 1/200sec, will freeze movement and action, while a slow shutter speed, for example 1/2sec, will enable you to show movement.
The third variable is aperture. This dictates how much light is able to reach the shutter via the lens and is measured in f-stops. For example, f2.8 is considered a wide aperture that lets plenty of light into the camera, while f22 is a narrow aperture that restricts the amount of light reaching the sensor. Wide apertures result in shallow depth of field, with plenty of out of focus areas, while narrow apertures result in lots of depth of field, with most of the image in focus.
As a general rule of thumb, narrow apertures demand slower shutter speeds and vice versa, but achieving the correct exposure is a matter of carefully balancing these three variables.
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