Optical zoom measurement
With a point and shoot camera, the more commonly used measurement to indicate the focal length range of the camera’s zoom lens is the optical zoom measurement. This measurement will be widely promoted in marketing materials, and it’s also listed in the specifications. (With the point and shoot camera the focal length range measurement is typically listed after the optical zoom measurement in the specifications list.)
The optical zoom is always listed as a number followed by the letter X. So a camera may have an optical zoom measurement of 8X.
This type of measurement is rarely indicated in the marketing materials for an interchangeable lens, even though it could be. To calculate the optical zoom for an interchangeable lens just divide the largest telephoto focal length at which the lens can record an image (such as 200mm in the example listed above) by the widest angle focal length of the lens (25mm in the above example). So 200 divided by 25 would yield an optical zoom measurement of 8X.