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 measurements for a digital camera signify the amount of magnification the lens can produce. The numbers can be confusing, however, because some manufacturers highlight different measurements, including optical zoom, digital zoom, and combined zoom. Keep this in mind when working at understanding zoom lenses:

Optical zoom is the most important zoom measurement because it measures the focal length range of the lens, based on the actual physical construction of the lens. As the camera moves the glass elements in the lens, the focal length for the lens changes, giving it the focal length range that's desired in a zoom lens.

A digital zoom lens is a focal length range simulation that the camera's software creates. Rather than moving the physical elements of the lens to change the focal length of the lens, the camera's software magnifies the image as displayed on the LCD screen, creating the illusion of a zoom lens. Because a digital zoom measurement just magnifies the image, it can result in a loss of sharpness in the photo, so using digital zoom isn't recommended unless you have no other choice. A smartphone camera can only use digital zoom.

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

Understanding Zoom Lens Numbers

Keep this in mind when working at understanding zoom lenses: All optical zoom measurements are not the same.

For example, a 10X zoom lens might have a 35mm film equivalent of 24mm-240mm. But another 10X zoom lens on another camera may have a 35mm-350mm equivalent. (This range of numbers should be listed in the specifications for the cameras.) 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 and 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 and you might assume that it provides strong telephoto capabilities, it might not be able to shoot at a telephoto setting as large as that of a 42X optical zoom lens. If the 50X optical zoom lens has a wide-angle setting of 20mm, its maximum telephoto setting would be 1000mm (20 multiplied by 50). And if the 42X optical zoom lens has a wide-angle setting of 25mm, its maximum telephoto setting would be 1050mm (25 multiplied by 42). Make sure you pay attention to not only the optical zoom measurement of a particular lens but also to its maximum telephoto setting.

It's also worth noting that some optical zoom measurements aren't a round number. You may find an optical zoom of 4.2X with a camera, such as for a 24-100mm focal length in an optical zoom lens.

For gaining a better understanding of zoom lenses in digital cameras, try reading "Understand the Zoom Lens".

Find more answers to common camera questions on the camera FAQ page.