What Is a Camera Zoom Lens Definition?

What do the numbers on camera zoom lenses mean?

Camera zoom lens definition
Understanding the numbers behind a 50X zoom lens can help you use it more effectively, such as with the Olympus SP-100. Olympus

The zoom lens measurement on a digital camera refers to how much the field of view can be expanded or contracted. The zoom specification may refer to one of three different measurements: optical zoom, digital zoom, or combined zoom.

Of these, optical zoom is the most important because it measures the focal length of the lens, which depends on its mechanical operation. As the camera adjusts the glass elements inside the lens, the focal length magnifies or contracts the field of view to the desired frame.

A digital zoom lens uses software to simulate the camera's focal length. Rather than adjusting the lens' mechanical components, a digital zoom lens magnifies the image as displayed on the LCD screen, creating the illusion of a zoomed-in field of view. This is the same technology smartphone cameras use to zoom in on an image. Because a digital zoom can only magnify an image, it usually results in a loss of resolution. Accordingly, digital zoom is only recommended if you have no other choice.

Some camera makers use the term combined zoom to describe their lens specifications, although this is an older term. Combined zoom refers to the measurement of both the optical and digital zooms when added together. 

Understanding Zoom Lens Numbers

Not all optical zoom measurements are alike. For example, a 10x zoom lens may have a 35mm film equivalent range of 24mm-240mm. But a 10x zoom lens on a different camera may have a 35mm-350mm equivalent. (This range should be listed in the camera's specifications.) The first camera will provide better wide-angle capabilities but less telephoto performance than the second camera.

An optical zoom lens can use almost any wide-angle or telephoto focal length setting. The optical zoom refers to the range between the two, regardless of its wide-angle or telephoto capabilities.

While a 50x optical zoom lens sounds like an impressive measurement, it is not necessarily better equipped to shoot at telephoto range as that of a 42x optical zoom lens. If a 50x optical zoom lens has a wide-angle setting of 20mm, then its maximum telephoto setting would be 1000mm (20 multiplied by 50). If a 42x optical zoom lens has a wide-angle setting of 25mm, then its maximum telephoto setting would be 1050mm (25 multiplied by 42). It's important to pay attention to the optical zoom measurement as well as the maximum telephoto setting.

Some optical zoom measurements are not round numbers. For example, it's not uncommon for cameras to have a 4.2x optical zoom lens with a 24-100mm focal length.

For a better understanding of digital zoom lenses, read this guide to digital zoom lenses: