Digital Photography Exposure For Dummies
Understanding the art and science of exposure in digital photography involves three main settings on your camera (which is probably a digital SLR, or dSLR): aperture, shutter speed, and ISO. Adjusting these interrelated settings will alter the look of your photos, and when you understand how these settings work, you'll begin to take the kinds of eye-catching and impressive photos that you probably dreamed about when you first invested in a quality digital camera.
Understanding How Your Digital Camera’s Exposure Settings Work
Taking great digital photos requires an understanding of how to use your digital camera’s exposure settings, whether you have an SLR camera or a point-and-shoot camera. The combination of shutter speed and aperture determines how much light hits the digital sensor in your camera, and the ISO setting determines how quickly the sensor responds to the light.
A simple way to illustrate how the three exposure settings work together is to think of filling a water bucket. Here are the components of this analogy:
A full bucket = a good exposure
The size of the bucket = the ISO
The size of the garden hose = the lens aperture
The amount of time it takes to fill the bucket = the shutter speed
Say you’re in your yard with a bucket and garden hoses of different sizes. The bigger the garden hose, the faster you can fill the bucket. You can fill the bucket by using any size garden hose you want, but the size of the hose determines how much time it takes to fill the bucket. If you want the bucket to fill up faster without using a bigger garden hose, you can use a smaller bucket.
To put the water-bucket analogy in photography terms, think of your camera’s digital sensor as a light bucket. Large apertures fill your sensor with light faster than small apertures. If you set your sensor to a faster ISO (in other words, if you make the bucket a smaller size), it’ll fill up with light faster than it would at a slower ISO setting. Large apertures (as well as high ISOs) call for faster shutter speeds. Small apertures (or low ISOs) require longer shutter speeds.
The Sunny f/16 Rule for Digital Exposure
The sunny f/16 rule, or Basic Daylight Exposure (BDE for short), tells you that the proper exposure in digital photography for a frontlit subject is f/16 with a shutter speed of 1/ISO (that’s 1 over the ISO in use). According to the sunny f/16 rule, at ISO 100, BDE would be f/16 at 1/100 second, and at ISO 200, BDE would be f/16 at 1/200 second.
When taking photos on a bright, sunny day, set the ISO of your camera to 100, the aperture to f/16, and the shutter to 1/100 second. Then go out and take pictures of some frontlit subjects. As long as your subject isn’t white or black, the exposures should be great. No metering necessary.
You can use equivalent exposures (different combinations of apertures, shutter speeds, and ISO settings that provide exactly the same exposure) for the sunny f/16 rule. The following table shows the equivalent exposures for the sunny f/16 rule at ISO 100.
Depth of Field Experimentation in Digital Photography
Controlling the depth of field (near-to-far sharpness) in a photo allows you to dramatically change the look of your digital images. Going for a lot of depth of field gives you a photo in which everything looks sharp from right in front of the camera to the distant horizon. When you want the subject to look sharp but you want everything in front of and behind the subject to look soft and blurry, opt for very little depth of field.
Three variables determine the depth of field in your digital exposures: aperture, focal length, and focused distance (the distance to your focused subject). Adjusting any one of these variables without adjusting the other two changes the depth of field. If you play with two or more of these variables, the depth of field may change even more dramatically; then again, it may not change at all.
To get the most out of depth of field requires a little experimenting. Start with these suggestions, but don’t hesitate to play around with your settings:
To minimize depth of field, use wide apertures and longer focal lengths and move in closer to your subjects. Also, try to avoid having distracting objects right behind your subject. A blurry tree or fencepost growing out of the subject is the kind of thing photographers tend to miss while they’re totally focused on their subject but kick themselves for when they look at the photos later.
If there’s a lot of distance between your subject and the background, the subject will pop out more against the blurry background.
To maximize depth of field, use smaller apertures and wide-angle lenses and back up a bit from your subject. How far back you need to get depends on the lens you’re using and the aperture you choose. Inexperienced photographers are prone to have boring foregrounds in their wide-angle, maximum-depth-of-field photos. To avoid this problem, have a center of interest close to the camera, even if it isn’t your main subject. It could be flowers, a cactus, a spot between the rails of a railroad track, or a yellow stripe in the highway. Whatever it is, put the camera down low and get in close. The center of interest will draw the viewer’s eye into the rest of the frame.
When you just need a medium amount of depth of field, stick with midrange apertures like f/5.6 or f/8 for wide-angle to normal focal length lenses. At longer focal lengths, switch to an aperture of f/11 or f/16.