How to Control Shutter and Aperture, and Why?

Together, the shutter speed and aperture control the exposure of an image. But what do these two assets of image construction really do?

The same thing. They both control how much light will reach the film (or digital sensor), but they do it very differently.

Think of a water faucet filling a one gallon bucket. To achieve this, you could fill the bucket fast by opening the valve to full. Or, you could fill the bucket, drop by drop, over a long period of time by only opening the valve slightly.

The time to fill the bucket is the shutter speed. The size of the valve opening, which affects how much pours into the bucket, is the aperture.

With varied shutter speeds, you can achieve dramatic differences in the resulting image. Imagine yourself on the sidewalk, photographing a car driving down the street. You are perpendicular to the car’s travel, and you are using a shutter speed of, say, 1/60 of a second (that’s a second, cut up into 60 pieces).

A car travelling at 35 mph moves approximately 50 feet every second (!). Assuming you hold the camera steady, the car will appear in one part of the frame when the shutter first opens, and at the end of the 1/60 sec., the car has moved a foot across the frame. During the exposure, the camera records the car at both places, and at every place in between. This is why the image is blurry; because the car literally ‘dragged’ across your frame by a foot over 1/60 of a second exposure.

What if we photographed the car at 1/1000 of a second? Cut a second up into 1,000 pieces, and the car barely has the chance to move a smidgen during your exposure. Sharpness, achieved.

Maybe you want the car sharp, like if you were shooting a race. Conversely, photographing the car with a little motion blur will add a sense1G4P4057a of movement. Either method is fine – it just depends on what you’re trying to convey with the image.

Aperture on the other hand, besides controlling the ‘flow’ of light, also controls depth of field. Depth of field is the degree to which things

are in focus across your frame. A large aperture (like f/2.8) will have little depth of field. A small aperture (like f/16) will have a much greater depth of field. As you can see by the numbers, small apertures have larger numbers, and vice versa.

A landscape photographer, shooting a scene with flowers in the foreground and a mountain in the back, will want to have the flowers and
the mountain in focus. He or she will therefore photograph the scene using a small aperture. What about the portrait photographer who wants the person sharp, but the background blurry? You got it, they’ll use a large aperture to achieve that effect.

Neither aperture nor shutter speed can be used by themselves. They are always used in combination to make an exposure. As such, varying one will affect the other – i.e., Use a large aperture (which lets a lot of light through the lens), and for a given exposure your shutter speed will not need to be as long as if you were using a small aperture.

So if you (or your camera) have determined a good exposure, you’ll then want to focus on the composition of the image

One Comment

  1. Comment by Abbie wild
    on June 26, 2013

    Thank you! A nice clear and concise explanation of the two features that a photography newby like myself should have a good grasp on.

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