What do the Numbers on Camera Lenses Mean? Understanding SLR Lenses

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Nearly all camera lenses will have some numbers and letters printed on them. Some of these numbers are part of the basic technical specification of the lens, and some indicate the features and capabilities that the lens is equipped with. A few of these terms will be common for all lenses, but some may be manufacturer specific. Let’s look at the common terms first, followed by manufacturer specific terminologies.

Common Terms/Numbers Found on Camera Lenses

Focal Length. For a prime lens, this will be a number mentioned in millimetres. A zoom lens contains two numbers indicating the lowest and highest possible focal lengths for the lens.

With zoom lenses, you can also see a series of numbers next to a slider or a rotating grip, with a pointer pointing to one of the numbers. This indicates the current focal length of the lens.

Examples: 50mm, 100mm, 17-40mm, 70-300mm. The first two numbers are for prime lenses with focal length 50mm and 100mm. The third one indicates a zoom lens whose focal length can vary from 17mm to 40mm. Similarly, the last one indicates a lens with focal length varying from 70mm to 300mm.

Focusing distance. This is a series of numbers mentioned in feet, usually starting from a few feet and going to infinity. This indicates the distance at which the lens is currently focused.

Minimum Focusing Distance. Most lenses indicate the minimum distance at which the lens can focus properly. This is usually mentioned in feet. This can be a single number for a prime lens and a range for zoom lenses. If the lens has macro capability, it is indicated by the picture of a flower.

Aperture. This is a set of numbers mentioned as a ratio that indicate the widest possible aperture for a lens. In case of a zoom lens, you can see one or two values, while a prime lens will have a single value.

Example. 1:2.8, 1:4-5.6. In the first example, the numbers indicate that the widest aperture possible for the lens is f/2.8, and this value remains constant at all focal lengths. In the second example, the value varies between f/4 and f/5.6 depending on the focal length.

Filter Diameter. This is a number at the far end of the lens mentioned in millimetres, usually preceded with the symbol of a line across a circle. This indicates the diameter of the lens thread where the filters are fitted.

AF/MF. This is a switch that can toggle between the two values. Setting the switch to AF turns auto-focus on. MF indicates manual focus.

Canon Lenses

EF: This is a term used by Canon on their auto-focus lenses that fit on their EOS cameras. It stands for electrofocus, and is seen on nearly all Canon lenses.

EF-S: These are lenses with mounts that can fit only on digital SLR cameras with smaller sensors. They are not compatible with cameras having full frame sensors or film cameras.

USM: This stands for Ultrasonic Motor, built for faster and silent focusing.

IS: IS stands for Image Stabilization, which is a feature to compensate for shake when taking pictures.

L: This indicates Canon’s top of the line L series lens which offers better image quality and performance.

DO: Indicates diffraction optics, which are smaller lenses that offer better image quality.

Nikon Lenses

AF-S or SWM: Both are terms used for lenses that have built in Silent Wave Motor.

DX: Lenses that can be fitted only on digital SLR cameras with smaller sensors.

VR: Lenses with built in Vibration Reduction (similar to Canon’s IS).

Sony Lenses

DT: Lenses that can be fitted only on digital SLR cameras with smaller sensors.

SSM: Lenses with Supersonic Wave motors that provide silent and faster auto-focus.

HS: Lenses with high speed motors that provide faster auto-focus.

D: A premium range of lenses that provide better image quality and performance.

Sigma Lenses

HSM: Lenses with a hypersonic motor that provide faster and silent auto-focus

OS: Indicates Optical Stabilizer - lenses with stabilization to prevent shake.

DC: Lenses meant for use with digital SLR cameras with smaller sensors.

EX: Lenses with superior build for better image quality and performance.

If you find yourself stumped on the meanings of other photography related abbreviations, please read Common Photography Abbreviations & Acronyms (CPAA) and Their Meanings.