A stop (might also be called an f-stop or an exposure stop) is a basic but important term in photography. You might hear someone say that a picture is “Underexposed by 1 stop” or “The picture is overexposed, turn the exposure down one stop.” The term “stop” is a relative term defining the amount of light in a picture.

If you increase the exposure by one stop, you double the amount of light in the picture. If you decrease the exposure by one stop, you halve the amount of light in the picture.

If someone says, “The picture is underexposed by 1 stop,” they’re making a comparison between the picture they see and what they think the proper exposure should be. If you double the amount of light in the image, it should look better.

So how do you adjust the camera settings to increase or decrease the exposure by one stop? Pick one of the three basic camera settings (aperture, shutter speed, or ISO) and make an adjustment.

Let’s go in reverse order from the simplest to the more complex. You’ve got a fairly limited number of ISO settings. A standard dSLR might include 100, 200, 400, 800, 1600, 3200, and 6400. Notice how each setting is double the setting before it. If you bump the setting up one (i.e. 400 to 800) and double the number, you’ve just increased the exposure by one stop and effectively doubled the light in your image. If you turn the setting down one (i.e. 400 to 200) and halve the number, you’ve just decreased the exposure by one stop.

Shutter speed is similar, although you’ll have many more options. Also, because of the way shutter speed is measured, it is a little counter-intuitive. Let’s consider a few options – 1/125th of a second, 1/250th of a second, and 1/500th of a second. If you go from 1/250th to 1/500th, you’ve just halved the amount of time the shutter is open and you’ve turned the exposure down one stop. Conversely, going from 1/250th of a second to 1/125th will increase the exposure by one stop. Note that your camera will probably also give you more options in between (like 1/160th and 1/200th). These intermediate settings are considered to be 1/3 of a stop – a more subtle increase or decrease in exposure.

Aperture is the most complex. Here, you’ve got numbers that represent the size of the opening allowing light through the lens – i.e. f/2.8, f/4.0, and f/5.6. The meaning of the numbers can be a bit confusing, so we’ll side step that for today. Just remember that the numbers don’t work like shutter speed or ISO. The difference between f/2.8, f/4.0, and f/5.6 is one stop each – but notice that there’s no doubling here. In fact, “doubling” the number f/2.8 gives you a two stop increase. Over time, you’ll probably memorize a lot of these aperture settings, but in the beginning there’s a fairly easy shortcut. Most modern cameras allow you to alter the aperture in steps equal to 1/3 of a stop. So, between f/4.0 and f/5.6, you can also choose f/4.5 and f/5.0. If you click the wheel to the right three times, you’ll go from f/4.0, to f/4.5, to f/5.0, to f/5.6. Three clicks either way will alter the exposure by one stop.

A little confused? That’s ok. Play around a bit. We’ll come back to this another day.