When you go to the beach do you want a sunburn, a nice healthy tan, or a pale complexion? You’re in control by how much you expose your skin to the sun. If I spend too much time outside without my hat, my balding head gets burned. That’s analogous to an over-exposed photograph, although the results usually aren’t so painful.

This month and the next few I’m going to help you make sense of the three variables that interact to affect photographic exposure: the sensitivity of the digital sensor (or film), how long the light strikes the sensor, and how big is the hole the light passes through. We call those the ISO, shutter speed, and aperture. I’ll get to each of those and how they interact in this and the next few installments, along with exposure compensation.

You may wonder why this is important if you always use your camera in its fully automatic mode. In full auto, your camera is measuring the light and setting the ISO, shutter, and aperture to expose the subject correctly. Taking control yourself gives you creative options you don’t have in full auto mode.

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