Last month I introduced the three things you can control on your camera that affect exposure: ISO, shutter speed, and aperture. I explained how changing the ISO setting changes the sensitivity of your camera’s sensor. If you missed it, or need a review, read about ISO here.

Shutter speed is this month’s topic. Choosing an appropriate shutter speed for your subject is a creative choice as well as being one of the variables that affect exposure. All cameras have a hole inside the lens that, when open, lets light hit the sensor (or film). The shutter controls how long the hole is open.

When the shutter is open for a very short time you are able to stop motion and freeze action. Conversely, a long exposure can blur a moving subject. If you’re hand-holding your camera you need to choose a shutter speed that is short enough to compensate for any movement of the camera in your hands. The longer the focal length of your lens the shorter the shutter speed needs to be to avoid camera shake.

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