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Photo 101 : Aperture < Previous | Next >
What affects the amount of light?
A photo is made when light falls onto the sensor of the camera. You can control the amount of by light that falls onto the sensor in three ways. Let’s use the example of a water basin to understand the theory.

Imagine that the basin is the sensor of the camera, and that water represents the amount of light that falls onto the sensor. Your task is to ensure that enough water fills the entire basin (i.e a proper exposure). If there is too much water (or light), the basin overflows and there’s over-exposure. And if there is too little water (or light), the basin isn’t filled and there’s under-exposure.

So far so good? Now let’s turn on the tap and let the water start flowing. In order to fill the basin with just the right amount of water, you have two basic controls:

a)the amount of time that you leave the tap open
b)the size of the tap opening
The longer you leave the tap open, the more water flows out.

The larger the opening of the tap, the more water flows out at any time.

So assuming your basin is not filled yet, you can leave the water running for longer periods until it’s slowly filled. Or if you’re rushing for time, you can open up the tap more to let more water gush out to fill the basin quickly.

The length of time that the water is allowed to flow out can be understood as the shutter speed. A slow shutter speed allows more water to fill the basin, or more light to fill the basin. And a fast shutter speed (turning on and off the tap quickly) lets less water out to fill the basin.
The size of the tap opening is known as the aperture. The aperture controls the amount of water (or light) that enters the basin (or sensor) at a given amount of time. So assuming that you can only turn on the tap for five seconds, a larger tap opening will give you more amount of water, and a smaller tap opening will give you less amount of water – given a fixed amount of time.

By controlling the length of the tap opening and the size of the tap, you can control the amount of water that fills the basin. Similarly, the shutter speed and aperture controls the amount of light that reaches the sensor.

Are you still with me? Hang in there, because the next explanation is slightly more complex (after that it starts getting simpler – I promise). Pay attention to the following section as they can be slightly mind-blogging for newbies to photography.
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