Lesson 3: Using a DSLR Camera
Lesson 3: Controlling Exposure with a DSLR Camera
Lenses and Aperture
Say you were inspired by the birdwatching pictures from Amherst College's Book & Plow Farm, and you decide to buy a zoom lens. You find a 300mm lens with f/4 as the widest aperture setting for $950. Then, you click over to look at a 300mm lens with f/2.8 as the widest aperture. It costs over $5,800.
"What!" you say to yourself, "the focal length and thus the magnification of both lenses are the same! How can one lousy aperture stop cost six times as much money?"
The answer is that in photography all stops are exponential. That means f/2.8 lets in twice as much light as f/4 does. If an indigo bunting lands on your bird feeder at dusk, then that extra stop could be the difference between a picture you can use and a picture you can't.
Setting shutter speed can be a practical choice based on how much light is available, but it can also serve as a creative storytelling choice. For example, shutter speeds less than 1/30th of a second can create motion blur, while shutter speeds above 1/250th of a second freeze the action in a way our own brain does not.
The slowest shutter speed you can hand-hold on a DSLR without getting motion blur is approximately 1/15th of a second. The exact boundry where involuntary motion blur begins will fluctuate depending on the focal length of your lens and whether or not your subject is in motion.
Choosing a Camera Mode
Whew! After all those scales and stops, you might be tempted to leave your camera in auto mode. But it's truly worth your time to practice in the manual modes of your DSLR until you're comfortable using them.
Learning to control exposure and depth of field isn't some useless abstraction. These techniques are frequently the difference between a successful visual story and a picture that doesn't quite work.