How to read a lens name

A lens name such as "FE 24-70mm F2.8 GM II" or "17-70mm F/2.8 Di III-A VC RXD" packs most of what you need to know into a line of numbers and codes. Once you can read it, you can tell whether a lens fits your sensor, how much light it gathers and roughly where it sits in a maker's range.

Start with the two numbers

Focal length

The millimetre figure is the focal length: a single number for a prime (50mm), a range for a zoom (24-70mm). Lower numbers show more of the scene, higher numbers less.

The figure on the lens is always its real focal length, not a "full-frame equivalent". A 33mm lens on an APS-C body frames about like a 50mm lens on full frame, because the smaller sensor crops the image by about 1.5 (1.6 on Canon APS-C). On Micro Four Thirds the factor is 2, so a 25mm lens frames like a 50mm.

Maximum aperture

The second number, written f/2.8, F2.8 or 1:2.8 on the barrel, is the widest the aperture opens. A smaller number means a wider opening and more light. Each step in the standard series (f/1.4, f/2, f/2.8, f/4, f/5.6) halves the light, which is one stop.

A wider maximum aperture gives faster shutter speeds in dim light and more background blur. The cost is size, weight and price. The figure is only the maximum: nearly every lens can close down from there.

Constant or variable

A zoom with one aperture figure, such as 24-70mm f/2.8, keeps that aperture across the whole range. A zoom with two, such as Fujifilm's XF18-55mmF2.8-4, is variable: f/2.8 at 18mm, narrowing to f/4 at 55mm.

Variable-aperture zooms are usually smaller, lighter and cheaper. Constant-aperture zooms keep exposure steady as you zoom, which matters most for video and for flash or manual exposure. On a cheap kit zoom of f/3.5-5.6, the long end is about 1⅓ stops darker than the short end.

Which sensor the lens covers

A lens made for APS-C projects a smaller image than one made for full frame. Each brand marks this differently:

• Sony: FE is full frame; E is APS-C (and Super 35 for video).
• Canon: RF is full frame; RF-S is APS-C, introduced in 2022. On older DSLRs, EF was full frame and EF-S APS-C.
• Nikon: FX is full frame and DX is APS-C. Z-mount APS-C lenses carry DX in the name (NIKKOR Z DX 24mm f/1.7); full-frame Z lenses usually don't say FX at all.
• Fujifilm: X-mount is APS-C only, so XF and XC lenses are all APS-C. GF lenses are for its GFX cameras, whose G-mount sensor is larger than full frame.
• Tamron: on current mirrorless lenses, Di III means full frame and Di III-A means APS-C. Some older Di III lenses were made for smaller sensors before the "-A" existed, so check the format on the spec sheet. Di and Di II are the DSLR equivalents.
• Sigma: DG means full frame and DC means APS-C. DN used to mark a lens designed for mirrorless (DG DN, DC DN). Sigma's newest names drop it: the 300-600mm F4 DG OS Sports and the 17-40mm F1.8 DC Art are both mirrorless lenses. An older "DG HSM" lens is usually a DSLR design.

An APS-C lens on a full-frame Canon RF or Nikon Z body makes the camera switch to a crop mode automatically, using only the middle of the sensor. Sony bodies do the same when their APS-C setting is on Auto. It works, but you lose much of the resolution you paid for. A full-frame lens on an APS-C body works normally and frames tighter.

Stabilisation codes

Each brand names its in-lens stabilisation differently, but they do the same job:

• OSS: Sony (Optical SteadyShot)
• IS: Canon, and OM System on lenses such as the 12-100mm f/4 IS PRO
• VR: Nikon (Vibration Reduction)
• OIS / O.I.S.: Fujifilm, and Panasonic (also Power O.I.S. and Mega O.I.S.)
• OS: Sigma
• VC: Tamron (Vibration Compensation)

Makers quote the benefit in stops, and the figure can depend on the body: OM System rates the 12-100mm at up to 5 stops on its own and up to 6.5 with a body that supports Sync IS. Your own results will vary.

Stabilisation corrects your hand movement, not a moving subject. When the body also stabilises its sensor, some systems combine the two: Panasonic calls this Dual I.S. and OM System Sync IS. Not every lens and body pair supports it, so check the maker's compatibility list. If your body has in-body stabilisation, an unstabilised lens is often fine at short and normal focal lengths.

Focus motor codes

The motor moves the focusing glass. The code tells you the type, not how well a given camera will track. That depends far more on the body.

• STM (Canon): a stepping motor, which Canon pitches as smooth and quiet for video. Nikon uses stepping motors too, in many Z lenses and its F-mount AF-P lenses, but doesn't put STM in the name.
• USM (Canon): ultrasonic motor. The ring type is fast and allows manual focus at any time; the cheaper micro type often doesn't.
• Nano USM (Canon): a newer ultrasonic design meant to combine USM speed with STM quietness.
• VCM (Canon): a newer focus drive, used on recent RF L primes such as the RF 35mm F1.4 L VCM.
• XD Linear (Sony): Sony's linear autofocus motor. It appears on the spec sheet, not in the name.
• LM (Fujifilm): linear motor, for fast focus.
• HSM (Sigma): Hyper Sonic Motor, mostly on Sigma's DSLR lenses.
• HLA (Sigma): High-response Linear Actuator, on newer mirrorless lenses. Sigma lists it in the specs, not the name.
• VXD, RXD, USD (Tamron): VXD is a linear motor, RXD a stepping motor, and USD the ultrasonic motor on many of Tamron's DSLR lenses.

Some codes appear in the name, others only on the spec sheet, so a missing code does not mean a missing motor.

Series marks: what they actually promise

Series marks place a lens in the maker's range. They do not promise a particular spec. Weather sealing, aperture and price still vary within a series, so read the spec sheet.

Sony G Master, G and ZA

Sony places G Master (GM) above G as its top line. The first G Master lenses arrived in 2016. ZA lenses carry the Zeiss name but are made by Sony, to designs Zeiss has approved.

Canon L

Canon's top range, marked with a red ring. Many L lenses are weather sealed and many L zooms have a constant aperture, but neither is guaranteed: the RF 100-500mm F4.5-7.1 L IS USM is variable.

Nikon S-Line

Nikon's higher optical tier for Z lenses, shown as "S" at the end of the name. It is not about speed: the NIKKOR Z 24-70mm f/4 S and the f/1.2 S primes are both S-Line. A non-S lens is not necessarily a poor one, so compare the specs.

Sigma Art, Contemporary and Sports

Sigma describes Art as aiming for the highest optical performance, Contemporary as combining optical performance with compactness, and Sports as its line for demanding conditions, mostly telephotos.

OM System PRO

The top tier of M.Zuiko lenses from OM System (formerly Olympus). OM System describes PRO lenses as weather sealed, and rates some, such as the 12-100mm f/4 IS PRO, to IP53. "IS PRO" means the lens also has its own stabilisation.

Leica DG and ASPH

Leica DG lenses are Panasonic Micro Four Thirds lenses sold under the Leica name. They borrow Leica family names such as Summilux and Elmarit. This DG has nothing to do with Sigma's DG.

ASPH means the lens contains aspherical elements, which correct some aberrations with fewer pieces of glass. Leica prints it on many of its lenses, as do most Leica DG lenses. Nikon uses aspherical elements too but lists them only in its specifications. It describes the design, not a quality grade.

Other codes you will see

• ED: extra-low dispersion glass, which reduces colour fringing.
• WR (Fujifilm): weather resistant. Fujifilm describes the benefit with the lens on a weather-resistant body; a sealed lens on an unsealed camera, of any brand, is not a sealed kit.
• R (Fujifilm): the lens has an aperture ring. XC lenses, Fujifilm's budget range, don't.
• PZ: power zoom, driven by a motor.
• Macro, MC (Nikon Z): a lens built for close-up work.
• TC: a built-in teleconverter, as on some long Nikon lenses.
• II, III, G2: a later version. It can be a full redesign, so compare the versions' specs.

The codes at a glance

Code	Brand	Means
FE / E	Sony	Full frame / APS-C
RF / RF-S	Canon	Full frame / APS-C
FX / DX	Nikon	Full frame / APS-C
Di III / Di III-A	Tamron	Full frame / APS-C mirrorless
DG / DC	Sigma	Full frame / APS-C
OSS, IS, VR, OIS, OS, VC	Various	In-lens stabilisation
STM	Canon	Stepping motor
USM, Nano USM	Canon	Ultrasonic motor
XD, LM, VXD	Sony, Fujifilm, Tamron	Linear motor
HSM	Sigma	Focus motor (mostly DSLR lenses)
GM, L, S	Sony, Canon, Nikon	Top optical series
A / C / S	Sigma	Art / Contemporary / Sports
PRO	OM System	Top series, weather sealed
ASPH	Leica, Panasonic	Aspherical elements

Reading a listing before you buy

Third-party lenses share one name across mounts. The Sigma 17-40mm F1.8 DC Art, for example, is made for L-Mount, Canon RF, Fujifilm X and Sony E. The mount is often a separate option or buried in the listing details, so check it before you pay. Our mounts page lists the bodies and lenses for each mount.

Retailers often shorten or reorder codes in titles. The maker's model code is more reliable: Sony's SEL codes (SEL2470GM2 is the FE 24-70mm F2.8 GM II) and Tamron's model numbers (B070 is the 17-70mm) confirm the exact version.

Lens names are generally the same in the US, UK, EU, Australia and Singapore. What changes is the warranty. Camera makers often give warranty cover only in the country or region of sale, so a grey import may have no local cover even though the name matches. Your rights against the seller come from local consumer law, which differs between those markets.

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