What Do the Numbers on a Zoom Lens Mean?
Zoom lenses can be attached to film and digital based single lens reflex (SLR) cameras. The barrel of the lens can tell you a host of information about the lens itself including its shooting capabilities, what size of filter can be attached, what focal lengths are available and maximum aperture settings.
Filters
Look for a circle with a line through it, followed by a number. This is the filter size of your lens. Common sizes range from 52 to 77.
Focal Lengths
Near the filter information will be numbers to indicate the focal range of the lens in millimeters. Some common zoom lens focal ranges are written as 17-35mm, 35-135mm and 70-200mm. The focal lengths available will also be written in increments on the barrel of the lens, near the zoom ring.
Aperture
After the focal range, will be a set of numbers indicating the largest aperture settings for that specific focal range. It will be written like 1:2.8-4. In this example, the largest aperture setting, on the wide end of the zoom lens, is 2.8. When the lens is zoomed to the longest focal length, the widest aperture available is 4.
Distance
Most lenses show a range of distances, measured in both feet and meters, on the barrel of the lens. This is used to estimate the distance from the camera to the subject when manually focusing the lens.
Extra Features
Some brands of camera lenses offer extra quiet focusing mechanisms and vibration reduction features, which are indicated on the barrel of the lens. Look for wording such as "silent wave motor," ultrasonic, USM (ultrasonic motor) and VR (vibration reduction).
Tags: barrel lens, focal range, aperture settings, focal lengths available, focal range will