The Exposure Triangle

Exposure plays very important part in taking good pictures. This determines whether your shot was properly exposed, underexposed or even overexposed.There are three main elements that need to be considered when playing around with exposure; ISO, Shutter Speed and Aperture. Aperture is ‘the size of the opening in the lens when a picture is taken. ISO is the the measure of a camera sensor’s sensitivity to light. Shutter speed is ‘the amount of time that the shutter is open’. These three elements forms the "Exposure Triangle".

To explain it simply, we'll take it like this.

Aperture is like a window. If it’s fully open, the  more light gets through and the room is brighter.

Shutter Speed is how long the window is open. The longer you leave them open the more that comes in.

ISO is the amount of noise you will see when you are inside the  room. The higher the ISO, the more noise you see in the room.

Aperture is measured in "f-stops",  for example f/2.8, f/4, f/5.6,f/8,f/22 etc. Moving from one f-stop to the next doubles or halves the amount of light that gets in. It also affects the Depth of Field (DOF). Depth of Field is the amount of your shot that will be in focus.

Higher f-stops(e.g  f/11 to f/22) means larger depth of field, while lower f-stops(e.g f/1.2,  f/1.4, f/1.8, f/2.8) gives you shallow depth of field.

Shot @ F/1.8 (Blown out background)

Shot @ F/11 (Larger Depth of Field)

Shutter speed is measured in seconds(1", 10", 20" ,etc ) or in most cases fractions of seconds(1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8). To freeze movement in an image you should have to choose a faster shutter speed and to let the movement blur you should have to choose a slower shutter speed.

1/400 Shutter Speed (Freezes the image)

20''  Shutter Speed (Light Trails and image blur)

The ISO speed(100, 200, 400, 800, etc) determines how sensitive the camera is to incoming light. A lower ISO speed(100, 200, 400) is almost always desirable, since higher ISO speeds dramatically increase image noise.

Shoot @ ISO 1600 (Can you see the noise?)

Remember that thinking about either Apperture, ISO, Shutter Speed in isolation from the other two elements of the Exposure Triangle is not really a good idea. As you change any of these elements, you’ll need to change one or both of the other elements to compensate for it.

For example if you speed up your shutter speed one stop (for example from 1/125th to 1/250th) you’re effectively letting half as much light into your camera. To compensate for this you’ll probably need to increase your aperture one stop (for example from f16 to f11). The other alternative would be to choose a faster ISO rating (you might want to move from ISO 100 to ISO 400 for example).