A camera lens with an AF/MF switch for autofocus or manual focus
The abbreviations labeled on a modern camera lens often include lens specifications to indicate focal length and maximum aperture. Certain lens abbreviations may refer to technology specific to one camera company. The manual included with the camera and lens usually explains each abbreviation to help you understand the various lens functions and specifications.
Focusing and Mechanisms
A lens capable of autofocus may have one or more of the following abbreviations, depending on the lens features and the camera manufacturer. AF refers to autofocus for automatic focusing on a selected point or area seen through the viewfinder. During autofocus, the camera's sensor, motor and controls work together to achieve a sharp focus. MF refers to manual focus that allows you to rotate the focus ring with your fingers until your subject appears in focus. Lenses with both autofocus and manual focus include a switch to select either focusing option.
IF stands for internal focus or inner focus. The inner lens group or groups can move without expanding or contracting the length of the lens barrel while focusing. RF refers to rear focus. This feature includes a system to activate the rear lens group for smooth autofocusing.
USM refers to ultrasonic motor. This lens-based DC motor technology starts focusing and stops when the subject appears sharp.
IS stands for image stabilizer. This technology is also known as vibration reduction (VR). Some interchangeable lenses include an image stabilization mechanism that works in low-light conditions. This feature can help reduce camera shake that causes blurry images.
Lens Elements
AL or ASP stands for aspherical lens. For example, a multi-element, wide-angle lens may include an aspherical lens element to minimize aberrations in images. An aspherical element has a complex surface profile that differs from a simple lens. The smaller and lighter aspherical lens offers better image resolution.
LD refers to Low Dispersion lens elements that compensate for chromatic aberration or lateral aberration seen as fringes of unwanted color. ED refers to Extra-low Dispersion lenses designed to minimize unnatural color shifts and color fringes that can degrade images. Images taken with LD and ED lenses usually appear sharper and clearer with more accurate color rendition.
Aperture
Interchangeable lenses with focal lengths and apertures labeled on the len barrels
The maximum aperture or opening of the lens is often designated with a colon between numbers, such as 1:4 to indicate a maximum aperture of f/4. The f-stop or focal ratio indicates a ratio of light or exposure on a standard f-stop scale. A low number such as f/1.8 has a wide aperture that allows much more light to enter a camera. A high f-stop number such as f/5.6 has a smaller aperture that allows less light to enter for recording.
Focal Length
The focal length of the lens shown in millimeters, such as 50mm, indicates the scope of the scene that the camera records. A wide-angle lens, such as 24 mm, offers a wider view than a telephoto lens, such as 300 mm, with a higher focal length to make distant objects appear closer.
Zoom Lenses
A zoom lens indicates two numbers to indicate the range of focal lengths available, such as 24 to 70 mm. Some lenses also show the range of apertures for the zoom lens, such as f/3.5 to 5.6. The range of f-numbers indicates the maximum aperture or opening for the zoom lens from its shortest focal length to the longest focal length. For example, a zoom lens set at 24 mm has a maximum aperture of f3.5; the same lens set at 70 mm has a maximum aperture of f5.6.
Small or compact cameras with a fixed lens often include an optical zoom. Magnification is indicated with an X, such as 3X.
Len Diameter
In the photography industry, the symbol ø followed by a measurement in millimeters (mm) represents the diameter of the front lens. For example, a lens showing "ø 67 mm" indicates a diameter of 67 mm. This lens diameter also indicates what size of filter and lens cap fits this lens.
Note that this diameter differs from the focal length of the lens, also represented in millimeters. For example, a zoom lens with a focal length labeled as 70 -- 200-mm may have a lens diameter of 67 mm or ø 67 mm.
Tags: maximum aperture, zoom lens, focal length, aspherical lens, focal length