Digital Photography

Zoom lenses let you change the magnification of an image without switching lenses. Zooms are designed to change the field of view of the lens while keeping the image in focus. When the field of view is widened (to take in more of the subject), the image must be reduced in order to fill the sensor or film area. This is the effect of using a short focal length lens or a wide-angle setting on a zoom. Conversely, when the field of view is narrowed (to take in less of the subject), the image must be magnified, again in order to fill the sensor or film area. This is the effect of using a long focal length lens or a zoom's telephoto setting.

The best way to use a zoom is to set it to the focal length you feel will produce the approximate effect you are aiming for. This method of working encourages you to think about the scene before ever raising the camera to your eye to compose the shot. It also makes you think ahead of the picture-taking process, rather than zooming in and out of a scene searching for any setting that seems to work. This is not only rather aimless, it is also time-consuming and can lead to missed photographic opportunities.

Many professional photographers use zooms almost as if they were fixed focal length, or prime, lenses, leaving them set to a favorite focal length most of the time. They then use the zoom control only to make fine adjustments to the framing. Zooms really are at their best when used like thiscutting out or taking in a little more of a scene. With a prime lens, you have to move the camera backward or forward to achieve the same effect. Depending on the type of subject you are trying to record, you could leave the zoom toward the wide-angle or telephoto end of its range. On some digital cameras, however, zooms are stepped rather than continuously variable, so they cannot be used for making small adjustments.

Tips

Distortion: Most zoom lenses distort the image by making straight lines look curved. This is especially the case at wide-angle settings.

Camera shake: At the very long effective focal lengths some digital cameras offersuch as a 35efl of 350 mmthere is a great danger that camera shake during exposure will reduce image quality. Make sure you hold the camera steady, preferably supported or braced, and use a short shutter time.

Lens speed: As you set longer focal lengths, the widest available aperture becomes smaller. Even in bright conditions, it may then not be possible to set short shutter times with long focal lengths.

Lens movement: Some lenses may take a few seconds to zoom to their maximum or to retract to their minimum settings. Don't be tempted to rush the action by pushing or pulling at the lens.