What happens when we “take a picture”? After all, we don’t physically carry anything away with us! When we hit the shutter button, the camera opens itself up and exposes its image sensor (or film) to the light of a particular scene, which it records and turns into a photograph. There are a few factors that determine how much light is absorbed, and therefore how bright a picture turns out. The balance between these factors is called exposure.
The word is used a lot in photography, so what does it mean? It has a few different connotations: a photography exposure is the moment when the shutter fires and makes an image. A long exposure is created when the camera exposes for an extended length of time (several seconds or more). A multiple exposure overlays the light from two or more scenes together.
The photo’s exposure, though, is a measure of how bright the image is. If an image is too dark, with no detail in the shadows and lacklustre highlights, it is underexposed; it didn’t get enough light. If the opposite is true – if it is overly bright – it got too much light, and is overexposed. You can alter the exposure value using exposure compensation, which is denoted by a [+/-] symbol. A camera will turn the exposure up and down using three variables:
The shutter is the mechanical door in front of the image sensor. It manages how long the sensor is exposed to light for. The long exposure we mentioned before is an example of a slow shutter speed, and will cause moving objects to blur across the frame. Conversely, a fast shutter speed will expose only for an instant, and will freeze motion. The shutter speed is expressed as a fraction of a second, such as 1/60th.
The size of the opening that lets light in through the lens is called the aperture. It can open wide or close down small, and affects the focus and sharpness of the photograph, from front to back, known as depth of field.
The ISO measures the recording surface’s sensitivity to light. When increased, it will respond more to the light that is available; this tends to produce noise or grain, degrading sharpness and image quality.
Each of these factors are measured in stops. A stop is a unit of light, defined as half or double the light of the next stop. This means that:
400 ISO is one stop higher than 200 ISO, and will absorb twice as much light; 100 ISO is one stop lower, and will absorb half as much.
A shutter speed of 1/250th of a second is one stop slower than 1/500th, and will absorb twice as much light; 1/1000th is one stop faster, and will absorb half as much.
F/5.6 is one stop wider than f/8, and will absorb twice as much light; f/11 is one stop smaller, and will absorb half as much.
Hopefully you’re beginning to see the pattern here! Because all of these factors are controlled by doubling or halving the light, you can lower one, raise another, and still have the exact same exposure value. For you math nerds out there, it works the same as the Mass/Density/Volume triangle, or Distance = Speed x Time – each variable balances the others to create the perfect exposure. Some of these options, such as ISO and exposure compensation, are available on the PicsArt camera; the others can be mimicked. For a more in-depth explanation of each corner of the triangle, including why and how to set the exposure on both a phone and a DSLR, stay tuned for our upcoming articles:
What is ISO – How To Use ISO on Digital and Phone Cameras
What is Shutter Speed – Conveying Motion
What is Aperture – Controlling Depth of Focus