Manual Controls and Your Digital SLR
The job of your digital SLR camera is to accurately measure the scene and produce a picture that accurately reflects it. Your job as a photographer is to analyze the scene, analyze what the camera gives you, and make modifications as necessary.
If you take control and supply one piece of the puzzle, the camera will supply the rest. When you’re taking certain types of pictures, it makes sense to determine which f/stop will be best for what you’re photographing. In other scenarios, it makes more sense to choose the shutter speed and let the camera determine the f/stop.
Shooting modes on digital SLR cameras
You choose a shooting mode and your digital SLR camera fills in the rest of the equation to render a properly exposed image. The camera modes that give you complete control over any picture-taking scenario include:
Aperture Priority: This gives you complete control over depth of field. You choose the aperture (f/stop number), and the camera chooses the shutter speed needed to properly expose the image.
A small f/stop number (large aperture) equals a shallow depth of field, and a large f/stop number (small aperture) equals a large depth of field. Depending on the lens you’re using, the f/stop range can be from f/1.4, which sends huge gobs of light into the camera, to f/32, which lets in a miniscule splash of light into the camera.
Shutter Priority: In this mode, your goal is to freeze or accentuate motion. You use a fast shutter speed to stop subjects in their tracks, or a slow shutter speed to create an artistic rendition of motion. You choose the shutter speed, and the camera calculates the aperture needed to properly expose the image.
Bulb: Choose this to keep the shutter open as long as the shutter button is fully depressed. This is also known as a time exposure.
Manual: You supply both the shutter speed and aperture for the effect you’re after. Most digital SLR meters show you guides in the viewfinder that let you know when you’ve picked a combination that results in a properly exposed image.
Understanding digital exposure
Digital cameras expose images the same way film cameras do. The duration of the exposure and the amount of light entering the camera determine whether the resulting image is too dark, too bright, or properly exposed.
The duration of the exposure is known as the shutter speed. Digital cameras have a shutter speed range from several seconds in duration to as fast as 1/8000 of a second. A fast shutter speed stops action, and a slow shutter speed leaves the shutter open for a long time to record images in low light situations.
Controlling depth of field
Depth of field determines how much of your image looks sharp and is in focus. For a shot of a landscape, you want an image that shows the blades of grass in the foreground to the distant mountains that disappear into the haze. Other times, when you’re shooting a portrait or taking a picture of a flower or bird, for example, you want a very limited depth of field.
You control the depth of field in an image by selecting the f/stop and letting the camera do the math to determine what shutter speed will yield a properly exposed image.
Understanding camera focal lengths
The focal length of the lens you use determines how the camera records the scene in front of you. A short focal length includes a wide view of the scene, which is why a lens with a short focal length is referred to as a wide-angle lens. A long focal length magnifies the scene, essentially capturing a small part of the scene (also known as field of view) and magnifying it to fill the frame. Lenses with long focal lengths are called telephoto lenses. A lens with a focal length that is 50mm encompasses the same field of view as the human eye.
A zoom lens encompasses a range of focal lengths. You can zoom in on your subject to focus on a small area, or zoom out for the big picture.