A typical SLR camera, whether film or digital, offers the option of attaching different lenses.
"Optical zoom" and "zoom lens" are two terms for the same thing. Glass parts inside the lens can be adjusted to change the focal length, making the object you're photographing appear closer. Zoom lenses used by serious photographers are interchangeable with other lenses, used for closeup or wide-angle shots. On the consumer market, many modern compact digital cameras have a built-in zoom option. The camera lens extends to change the focal length.
Consumer Digital Cameras
Many modern consumer compact cameras offer a zoom option.
Many consumer cameras offer a limited telephoto option that extends the lens mechanically to achieve a greater focal length, commonly referred to in marketing as "optical zoom." These cameras also often offer a "digital zoom," which is simply a digital enlargement of a section of the image. Image quality on digital zoom cannot match the image quality obtained by traditional optical zoom.
Variety of Zoom Lenses Available
Zoom lenses can be attached to SLR camera bodies in place of the regular lens.
Most SLR cameras, whether digital or film, are basically camera bodies to which a variety of lenses can be attached. Telephoto zoom lenses allow photographers to capture details that might easily be missed by the unaided eye. Thousands of varieties of zoom lenses available. For example, Canon's EF 100-400mm gets in close on long-distance shots, but it is large and bulky, making it awkward to work with. It also works within a specific range, making it a specialty lens for specific photographic projects. On the other side, a zoom lens like the EF 28-300mm, while still large and bulky, has a broader focal point, lending itself to uses other than getting in close on distant subjects.
Limitations to Built-in Optical Zoom
Optical zoom -- while better than digital zoom -- is limited by physical size. Those small, standard lenses are only so good and will extend focal length only so far. Due to the nature of the compact consumer camera, adding more lenses would detract from one the primary allure of these products -- they are simple, lightweight, and compact.
Limitations to Zoom Attachments
The main problem with using standard SLR zoom lenses is that they must be carried around in case they are wanted. Because they are an attachment, zoom lenses for the most part are a bulky addition to a photographer's equipment. Depending on size, a zoom lens can add several pounds of weight. Some are as large as telescopes and require their own support in the form of a mono-pod to achieve image stabilization. Most zoom lenses require lower shutter speeds, more light, or a combination of both to achieve desired results.
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