3.4 USING SHUTTER SPEED AND APERTURE TOGETHER

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Both shutter speed and aperture affect the exposure, the total amount of light reaching the image sensor, and so control a picture’s lightness or darkness. The shutter speed controls the length of time the image sensor is exposed to light and the aperture controls the brightness of that light. You, or the camera’s autoexposure system, can pair a fast shutter speed (to let in light for a short time) with a wide aperture (to let in bright light) or a slow shutter speed (long time) with a small aperture (dim light). Speaking of exposure only, it doesn’t make any difference which of the combinations is used. But in other ways, it does make a difference, and it is just this difference that gives you some creative opportunities. You’re always balancing camera or subject movement against depth of field. This is because a change in one causes a change in the other. Let’s see why.

Each setting is 1 "stop" from the next and lets in half or twice the light of the next setting. A shutter speed of 1/60 sec. lets in half the light that 1/30 sec. does, and twice the light of 1/125 sec. An aperture of f/8 lets in half the light that f/5.6 does, and twice the light of f/11. If you make the shutter speed 1 stop slower (letting in 1 stop more light), and an aperture 1 stop smaller (letting in 1 stop less light), the exposure doesn’t change. However, you increase the depth of field slightly and also the possibility of blur.

For general shooting you need a medium shutter speed (1/60 sec. or faster) and a medium aperture (f/5.6 or smaller). Slower shutter speeds will show up on the image as overall blur unless you support the camera, perhaps with a tripod.

• For fast-moving subjects you need a fast shutter speed (although the focal length of the lens you are using, the closeness of the subject, and the direction it’s moving also affect motion).
• For maximum depth of field, with the entire scene sharp from near to far, you need a small aperture (although the focal length of the lens and the distance to the subject also affects depth of field).

Photographing these fast-moving Blue Angels from the deck of a moving boat took a fast shutter speed to prevent blur caused by subject or camera movement. Great depth of field was also needed to keep the boats in the foreground and background sharp.