Test Knowledge

02. UNDERSTANDING EXPOSURE WHAT HAVE WE LEARNED?

CONTROLLING LIGHT with your SLR camera is a lot like controlling the water filling a cup. In photography, it takes a set amount of light for a proper exposure, similarly, it takes a set amount of water to fill a cup. Too much water and the cup overflows; too much light and your image is over exposed.

Light controls with the camera include; shutter speed, aperture and ISO. With the water analogy, the valve on the tap controls how long the water flows, how much it flows, and the size of cup to fill. The shutter speed on the camera acts like a gate, allowing light to enter the camera for an amount of time, exposing the image. Turning the tap on, then off, allows water to flow for a set amount of time, filling the cup. The tap can control how long the water will flow.

The aperture on the camera controls the volume of light that enters, exposing the image. The bigger the hole in the lens, the greater the volume of light shines through. The aperture can also be stopped down to a tiny hole. Similarly, with the water analogy, the more you turn on the tap, the greater the rate the water will flow. The tap’s valve can control how much water will flow through, ranging from a torrent to a slow drip. Finally, the ISO on a camera is a setting that changes how sensitive the image sensor is to light. The higher the number, the more sensitive it will be, thus requiring less light to get the proper exposure. This can be illustrated in the water analogy by changing the size of the cup. If you make the cup smaller, it takes less water (ie: light) to fill it up (or less light for a proper exposure).

The three light controls, and the three water controls work the same way. If you have a slow dripping tap, the water will have to run longer to fill up the cup.

If you turn on the tap full blast, it will take a very short amount of time to fill the cup.

If you have a smaller cup or bigger cup, then it can change how the flow rate and length of time the water flows for the cup to be filled.

Large Aperture

Exposure Unchanged

High ISO Small Aperture

Exposure Unchanged

Low ISO

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