The term “zoom lens” is commonly used in photography, but many people don’t understand exactly what it means. On cameras that use interchangeable lenses, such as SLR (single lens reflex) cameras that are most commonly used in professional photography, there are literally thousands upon thousands of lenses that can be used.
The Prime Lens
“Prime” lenses are lenses that have a fixed focal length. In other words, the view in the viewfinder is always the same in terms of how much of the scene will be in the shot. There are wide angle lenses, which take in more of the scene, standard lenses, which give a natural perspective as your eye would see it, and telephoto lenses, which is like looking through a telescope.
Wide angle lenses and standard lenses are commonly used in architectural, landscape, and product photography, Telephoto lenses bring the subject closer and are most commonly used in sports photography.
In portrait photography, such as head shots, a lens slightly more telephoto than a standard lens in commonly used.
Of course, there are always exceptions to the above.
The Zoom Lens
So what is a “zoom” lens? It is a common misconception that a zoom lens is always a telephoto lens. This is not necessarily so. The “zoom” description only indicates that the lens has the ability to change it’s focal length by turning a ring on the lens. This gives an infinite amount of adjustment of the focal length within the limits of the lens, thus making it easier to compose a shot without moving the camera. The zoom range is typically limited to the basic type of lens, such as wide angle or telephoto. A wide angle zoom may go from super wide to wide, a telephoto zoom may go from moderate telephoto to telephoto. Many lenses do cross over from wide angle to telephoto, but they will not be extreme at either end. In the picture, both lenses are zoom lenses, the lens on the left is a telephoto zoom, the one on the right goes from moderate wide angle to very slight telephoto.
So Why Even Bother With Prime Lenses?
The zoom lens is all about convenience. Two lenses can take the place of quite a few prime lenses. This is why DSLR “kits”, which is a camera body and one lens bundled together for sale, always feature a zoom lens which goes from moderate wide angle to slight telephoto. But as with anything, convenience can have it’s price, and not just monetarily. The image quality throughout the range of a zoom lens is rarely equal to a prime lens of the same focal length. Things like distortion in the final image, reduced sharpness, unwanted optical irregularities; all of these would typically be worse in a zoom lens. Now this is not to say a zoom lens cannot produce high quality images. The good ones can and do. But they are a compromise. We use zoom lenses all the time in our commercial photography business, for architecture, product photography, food photography, etc.. The lenses we use are generally are of a much higher quality and therefore more costly.
For most folks purchasing a DSLR camera, zoom lenses are just fine and a huge convenience, But keep in mind that as quality goes up, cost goes up. A $200 zoom lens will not perform as well as a $700 zoom lens, in many respects. There are also ‘super zoom’ lenses that go from very wide to very telephoto. These are the most convenient, but also have the most design compromises.