An Overview of Exposure for Digital Cameras

So you're ready to take the camera off automatic and tackle that manual mode, huh? Don't worry, it's not as bad as you think. Surely you'll need to play around a bit, and reading this one article won't fill you in on everything you need to know.

But when you boil it down, there are three basic settings you need to understand: aperture, shutter speed, and ISO. When you know how they work together, you can put your camera in manual and figure out (maybe with a little trial and error) how to properly expose your photo. Below you'll find a brief overview of what each setting does and links to some more thorough reading.

Aperture - The Size of the Opening

Deep inside your camera is a digital sensor. That sensor is covered by a round opening that opens and closes. That opening is called the aperture.

Open the aperture wider, you'll let in more light. Close the aperture a bit, and you'll let in less light. Unintuitively, a larger number (i.e. f/11 to f/22) means the aperture is getting smaller, while a smaller number (i.e. f/4 to f/2.8) means the aperture is getting larger. Here's an article on how the aperture affects exposure for some more detail.

The size of the aperture also determines your "depth of field." For now, we'll just say that a large aperture (i.e. f/2.8) will help blur the things on the outskirts of your picture while a small aperture (i.e. f/8) will help keep a large group of people in focus. For some examples and a bit more thorough of an explanation, check out this article on the aperture and depth of field.

Shutter Speed - How Long the Shutter Is Open

That sensor in your camera is also covered by a pair of doors - the shutter. When you press the magic button, these shutters open, let in some light, and then close. The amount of time they stay open is the shutter speed (usually measured in fractions of a second).

Increase the shutter speed, or make it faster (i.e. 1/125th of a second to 1/250th of a second), and you cut down on the amount of light coming in. Slowing down the shutter (i.e. 1/60th of a second to 1/30th of a second) will do the opposite. You can read more about shutter speed and exposure here.

The trade-off here is motion blur. If you have a really slow shutter speed (1/15th of a second, 1/8th of a second, or maybe even a full second) there's a chance that your subject will move while the shutter is open. This creates a blurring effect. For sports, you'll need a really quick shutter speed (1/250th of a second or faster), but late night photography might require a much longer, slower shutter. You can see some examples in this article on shutter speed and motion blur.

ISO - The Sensor's Sensitivity

Finally, there's a cryptic setting called "ISO." The simple explanation is this measures how sensitive your sensor is to the light.

If you turn the ISO up (i.e. 400 to 1600), you artificially increase the sensor's sensitivity and magnify the amount of light coming in. Instantly brighter picture! But this electrical manipulation also brings with it noise - annoying little speckly dots on your photo. The higher the ISO (and the cheaper the camera), and the more noise you'll see.

Change One, Change Another

Each of these three settings affects how much light comes into your image - the exposure. But each also has a side effect that can make or break your image. What's the point of having a well exposed image of a football field if the shutter stays open for a full second and the players are a blurry mess...?

Once you find the correct exposure, you can play around with the settings to get that perfect affect. Just remember to change them in tandem. If you open up the aperture, either speed up the shutter or turn down the ISO. Likewise, if you slow down the shutter for some intentional blurring, make sure you close up the aperture to maintain the proper exposure.