Zoom Lens
Zoom Lenses © copyrighted 1999

Years ago, a well-equipped 35mm photographer carried a large camera case whenever he wanted to take pictures. It typically contained a camera body, a 50mm normal lens, a 28mm wide-angle lens, a 35mm semi-wide lens, an 85 or 105mm lens for portraits, a 135mm telephoto and a 200mm telephoto. This arrangement of lenses enabled him to cover just about any photographic situation. There were several drawbacks though. This many lenses took up quite a bit of space in a camera bag and were a burden to carry. Secondly, a photographer with all these fixed focal length (non-zoom) lenses constantly had to choose which lens to use for a particular photo and he spent a lot of time changing lenses. Many shots were lost because he was changing a lens when the photographic situation was at its peak, or the wrong lens was on the camera. Thirdly, a camera case full of lenses was an expensive investment.

Zoom lenses have changed all that. Instead of lugging around a half-dozen fixed focal length lenses, a photographer can cover the same focal range with two or three zooms. Not only is the camera case easier to carry, the zooms offer instant reaction to changing subject matter. A zoom lens lets you zoom in for a tighter shot that singles out the subject and makes it stronger. Conversely, you can zoom out for a panorama effect that shows more of the scene. Zoom lenses offer flexibility and versatility that can't be matched by fixed focal length lenses.

Zoom lenses are available in many focal length ranges. Shown here (from left to right) are 75-300mm, 120-600mm, 28-85mm, 35-70mm and 70-210mm zoom lenses.

Zoom lenses for 35mm cameras have been around for many years. Early zooms were big, heavy, expensive and left much to be desired in terms of optical performance. The selection of zooms and the focal length ranges they covered were equally limited. Improvements in design, lens coatings, alloys and plastics plus evolution are now providing us with zooms that are reasonably priced, cover a wide zoom range and virtually match the image quality of fixed focal length lenses.

Zoom lenses are available in just about the same range of focal lengths as non-zoom lenses. Mid-range zoom lenses cover wide-angle, normal and telephoto at the other. Mid-range zoom lenses cover wide-angle, normal and telephoto focal lengths all in one lens, giving them unmatched versatility. There are quite a few focal length combinations in this category including 35-70mm, 35-105mm, 35-135mm, 28-85mm, 28-135mm, and even 28-200mm. The 35-70mm has a comparatively narrow zoom range, but it is quite compact and is commonly used as a substitute for a 50mm normal lens. The other mid-range zooms are larger and heavier, but can be used in place of normal lenses, too. Telephoto zoom lenses are widely used for portraits, travel, scenics, sports and candid photos. Zooms in the range of 70-210mm and 80-200mm are very popular because they cover the most commonly used telephoto focal lengths and can be hand-held without much difficulty. Longer zooms such as 75-250mm, 75-300mm, 100-300mm and even 120-600mm are available too. They are useful for sports and wildlife photography. Long zooms can be used for many of the same purposes as shorter telephoto zooms, but they are larger, heavier and often slower in speed.

Zoom lens features Macro focusing.
Most zoom lenses have macro focusing, which means the lens can focus close up. A reproduction ratio is usually given which indicates how close a lens can focus. For example, a 1:4 ratio means the lens can focus close enough so an object that measures four inches in diameter will measure one inch in diameter on the slide or negative. (A 1:4 ratio is often called 1/4th life-size.) How a zoom lens is set for macro focusing varies. Some zooms have continuous macro focusing, which means you simply turn the focusing ring until it stops at the minimum focusing distance. You can still zoom in and out to control the subject by having the zoom control set at the longest focal length. (For example, 210mm with a 70-210mm zoom.) Other zoom lenses have a special setting for macro focusing. Usually, the zoom/focus ring is turned to the minimum focusing distance and it will engage into a macro focusing setting at one end of the focal length range. This limited macro focusing is not quite as easy to use and is more restricted than continuous macro focusing, but it's adequate for taking occasional close-up photos.
One-touch zoom control.
Most zoom lenses have one-touch zoom control. A single ring on the lens barrel is turned to adjust focus and is pushed and pulled to control the zoom. If a zoom lens isn't a one-touch, it has two separate rings. One controls the focus while the other controls the zoom action.
Lens aperture. Some zoom lenses are described as having one maximum aperture, such as 75-205mm f3.8. The f-number remains constant throughout the zoom range. Other lenses have two maximum apertures included in their descriptions, such as 28-80mm f2.8-4.0. This means that the f-number gradually changes as you zoom from one end of the zoom range to the other. At the shorter end of the zoom range, the lens is "faster" than at the other end. Each f-number changes as the lens is zoomed, not just the maximum aperture. A shifting lens aperture is not as much of a problem as it seems, though. The camera's exposure control system will still compensate for the gradual lens speed change.

Mid-range zoom lenses like the 28-80mm shown on this SLR are commonly used as substitutes for 50mm normal lenses. They cover wide-angle, normal and telephoto focal lengths in a single lens, a very flexible combination.

Points to consider when buying a zoom lens
¥ Focal length range. How do you intend to use this lens? If it will be mostly for vacations and traveling, perhaps a mid-range zoom having both wide-angle and short telephoto coverage will be best. If you're more interested in a lens for portraits and sports photos, a telephoto zoom such as a 70-210mm will be a good choice.
¥ Size and weight. The physical size and weight of a lens may be important to some, less important to others. Generally speaking, the faster the lens, the bigger and heavier it will be. A lens having a very wide zooming range will be significantly larger than a lens with a more limited range.
¥ Lens Speed. If you will be using the lens for indoor use or for photographing action, the lens speed is more important than when the lens is used outdoors photographing stationary objects. A faster lens (with smaller f-number) lets in more light than a slower one. This make it easier to take pictures in subdued lighting. More importantly, it makes the viewfinder brighter and easier to focus.
¥ Filter size. If you use filters extensively and have a collection of them in one size, you'll want the new zoom to accept that same filter size if possible.
¥ Macro focusing. If you are interested in taking close-up photos, check how the lens is used for macro work. A lens having continuous macro focusing is more flexible than one with limited macro focusing.
¥ Price. Zoom lenses are available in a wide range of prices. The preceding points have a great deal to do with the price of a zoom lens. A more expensive lens will most likely be faster than a less expensive lens. It may have continuous macro focusing while the less expensive one has limited macro focusing, too.