Zoom lens

A zoom lens allows you to change focal lengths without changing lenses. It has variable focal lengths, enabling it to be used as a wide-angle lens for one exposure, then as a normal or telephoto lens for another, depending on its range of focal lengths. Some zooms cover a range of mainly telephoto settings, from 70 mm to 300 mm, for example, or 80 mm to 200 mm, whereas others provide a selection of wide-angle focal lengths, such as 17 to 35 mm. Popular, all-around-use zooms range from moderate wide-angle to moderate telephoto.

A zoom’s range is generally indicated by its widest and narrowest focal lengths, for example 70-300 for a lens that zooms from 70 mm to 300 mm. There is often an arrow between the numbers to indicate that it is a zoom.

Zoom lenses provide the photographer with flexibility in framing images while remaining in one camera position. With a 70-300 zoom, for instance, you can take a three-quarter-length shot of someone at the 70 mm setting, a head and shoulders portrait at 105 mm, and shoot a distant wild animal at 300 mm.

The main disadvantages to zoom lenses are that they are often heavy and slow. Many have maximum apertures no faster than ƒ/4 or ƒ/3.5 at their widest focal length. High-quality, faster zoom lenses can be prohibitively expensive, if available at all for your camera model. A good quality zoom lens is of particular use in aerial photography and for speed and versatility when photographing weddings.

Some Zoom Lens Drawbacks

Although choosing a point-and-shoot camera with a large optical zoom lens is desirable for many photographers, it sometimes presents a few minor drawbacks.

• Noise. Some beginner-level, inexpensive cameras suffer from lower image quality because of noise when the lens is extended to the maximum zoom capability. Digital camera noise is a set of stray pixels that don't record correctly, usually appearing as purple edges in a photo.
• Pincushioning. Maximum zoom also sometimes causes pincushioning, which is a distortion where the left and right edges of the photo appear stretched. Horizontal lines appear slightly curved toward the middle of the frame. Again, this problem usually is limited to beginner-level, inexpensive cameras with large zoom lenses.
• Slower shutter response time. When using the maximum zoom magnification, the shutter response time sometimes slows, which may cause blurry photos. You also could miss a spontaneous photo because of the slower shutter response. It simply takes the digital camera longer to focus on the image at the maximum zoom setting, which explains the slower shutter response time. Such problems are magnified when shooting at maximum zoom in low light.
• Requires a tripod. Using a long zoom lens can cause increased camera shake. Some digital cameras can correct this problem through image stabilization. You also can use a tripod to prevent blurry photos from camera shake.