A quick peek at the barrel of your camera’s lens reveals a jungle of letters, numbers, and acronyms. What exactly do they all mean and how can you translate the codes into useful information?
Today’s Question & Answer session comes to us courtesy of Photography Exchange—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites. Image courtesy of Canon, USA.
The Question
Photography Exchange reader Mikal Sundberg is curious about the markings on his camera lens. He writes:
So what kind of decoder ring do you need to make sense of the code?
Examples, Nikon: Nikon AF-S DX 16-85mm VR f/3.5-5.6G IF-ED Nikon AF-I 600mm f/4D IF-ED Nikon AF-S VR Micro-NIKKOR 105mm f/2.8G IF-ED
Examples, Canon: Canon EF 85mm f1.2L USM Mark II Canon 70-300mm f/4.5-f/5.6 DO IS
Examples, Sigma: Sigma 150mm F2.8 EX APO DG HSM Macro Sigma 70-200mm F2.8 EX DG OS HSM Sigma 50-150mm F2.8 EX DC APO HSM II
How do I decipher the lens names from different manufacturers?
The Answers
Photography Exchange contributor Jrista offers up a very comprehensive answer. We won’t judge you if you skim through his expansive write up until you find your specific brand of camera equipment.
If you’re scratching your head now because you’ve learned the term but you don’t know what it means, another Photography Exchange user Hamish Downer is here to help:
Canon Lenses
Canon lenses use the following terms to indicate features of each lens:
Common XYZmm: Focal length f/x. y: Maximum aperture Focus/Mount Type EF: Electronic Focus EF-S: Short-Back Electronic Focus EF-M: Mirrorless Electronic Focus TS: Tilt-Shift TS-E: Tilt-Shift, Electronic aperture control MP-E: Macro-Photography, Electronic aperture control Features IS: Image Stabilization USM: Auto Focus Type: Ultrasonic Motor STM: Auto Focus Type: Stepping Motor (Mark) N: Version of lens (Mark II = v2, Mark III = v3, etc. , word Mark may not be present) DO: Diffractive Optics L: Luxury series Macro: close focusing, but not necessarily 1:1 magnification Softfocus ability to use soft focusing for smooth dreamy look PF Power Focus
Examples
XYZmm: Focal length f/x. y: Maximum aperture
EF: Electronic Focus EF-S: Short-Back Electronic Focus EF-M: Mirrorless Electronic Focus TS: Tilt-Shift TS-E: Tilt-Shift, Electronic aperture control MP-E: Macro-Photography, Electronic aperture control
TS-E: Tilt-Shift, Electronic aperture control
IS: Image Stabilization USM: Auto Focus Type: Ultrasonic Motor STM: Auto Focus Type: Stepping Motor (Mark) N: Version of lens (Mark II = v2, Mark III = v3, etc. , word Mark may not be present) DO: Diffractive Optics L: Luxury series Macro: close focusing, but not necessarily 1:1 magnification Softfocus ability to use soft focusing for smooth dreamy look PF Power Focus
Canon EF 16-35mm f/2. 8 L II USM Lens Canon EF 70-200mm f/2. 8 L IS II USM Lens Canon TS-E 17mm f/4 L Canon EF 50mm f/1. 2 L USM Canon EF-S 10-22mm f/3. 5-4. 5 USM
Nikon Lenses
Nikon lenses use the following terms to indicate features of each lens:
Common XYZmm: Focal length f/x. y: Maximum aperture Lens System DX: Digital, Short Back FX: Full Frame (film or digital) Lens Mount AI: Automatic Indexing mount (includes metering sensor) AI-S: Improved Automatic Indexing mount IX: Lenses designed specially for APS film SLR-s; their rear end protrudes too much to allow using them on a 35mm film camera or a dSLR Serie E A cheaper serie of AI-S where plastic replaced some metal parts. Not designated as Nikkor but “Nikon Lense Serie E” Focusing System AF: Auto Focus, built into camera AF-S: Auto-Focus Silent (Silent Wave Motor, required for bodies without focus motor) AF-I: Auto-Focus Internal AF-N: Auto-Focus (improved version, rare) Features Reflex: Catadioptric (mirror) lense. D: Distance, communicates focus distance for 3D Matrix metering mode and also for flash autoexposure. All AF-I, AF-S, and G-type lenses are also D-type. (Indicated after the f-number in the name, sometimes designated as AF-D). SWM: Silent Wave Motor N: Nano-Crystal Coating NIC: Nikon Integrated Coating (multicoated lenses) SIC: Super Integrated Coating (multicoated lenses) VR: Vibration Reduction ED: Extra-low Dispersion Glass FL: Fluorite. Designated a lens with some element in fluorite instead glass. ASP: Aspherical Lens Element IF: Internal Focusing RF: Rear Focusing RD: Rounded diaphragm Micro: Enable high reproduction ratio. Typically at 1:1 or 1:2. G: No aperture ring (automatic aperture only) DC: Defocus Control PC: Perspective Control. Lenses with shift feature (older) and newer with tilt as well. E: Electronic diaphragm. Some lenses with an electronic diaphragm. Only supported by bodies from D3 and after. P: CPU enabled version of AI-S lenses (Sometimes designated as AI-P)
Examples
XYZmm: Focal length f/x. y: Maximum aperture
DX: Digital, Short Back FX: Full Frame (film or digital)
AI: Automatic Indexing mount (includes metering sensor) AI-S: Improved Automatic Indexing mount IX: Lenses designed specially for APS film SLR-s; their rear end protrudes too much to allow using them on a 35mm film camera or a dSLR Serie E A cheaper serie of AI-S where plastic replaced some metal parts. Not designated as Nikkor but “Nikon Lense Serie E”
AF: Auto Focus, built into camera AF-S: Auto-Focus Silent (Silent Wave Motor, required for bodies without focus motor) AF-I: Auto-Focus Internal AF-N: Auto-Focus (improved version, rare)
Reflex: Catadioptric (mirror) lense. D: Distance, communicates focus distance for 3D Matrix metering mode and also for flash autoexposure. All AF-I, AF-S, and G-type lenses are also D-type. (Indicated after the f-number in the name, sometimes designated as AF-D). SWM: Silent Wave Motor N: Nano-Crystal Coating NIC: Nikon Integrated Coating (multicoated lenses) SIC: Super Integrated Coating (multicoated lenses) VR: Vibration Reduction ED: Extra-low Dispersion Glass FL: Fluorite. Designated a lens with some element in fluorite instead glass. ASP: Aspherical Lens Element IF: Internal Focusing RF: Rear Focusing RD: Rounded diaphragm Micro: Enable high reproduction ratio. Typically at 1:1 or 1:2. G: No aperture ring (automatic aperture only) DC: Defocus Control PC: Perspective Control. Lenses with shift feature (older) and newer with tilt as well. E: Electronic diaphragm. Some lenses with an electronic diaphragm. Only supported by bodies from D3 and after. P: CPU enabled version of AI-S lenses (Sometimes designated as AI-P)
Nikon AF 85mm f/1. 8 Nikon AF 85mm f/1. 8D Nikon AI 500mm f/4. 0 P Nikon AF-S DX 16-85mm VR f/3. 5-5. 6G IF-ED Nikon AF-I 600mm f/4D IF-ED Nikon AF-S VR Micro-NIKKOR 105mm f/2. 8G IF-ED
Olympus 4/3 lenses
Common XYZmm: Focal length 1:x. y: Maximum aperture Features ED: Extra-low dispersion glass elements SWD: Auto Focus Type: Supersonic Wave Drive Motor N: Version of lens (II = v2, III = v3, etc. )
Pentax lenses
Common XYZmm: Focal length 1:x. y: Maximum aperture Focus/Mount Type K, M: Manual Focus, Manual/Aperture priority metering AF: Early AF system with AF motor and electronics in lens that works only with ME-F body. A: Manual Focus, supports Shutter priority and Program exposure metering F: Adds Auto Focus to capabilities of A lenses FA: Adds ability to communicate MTF to body to capabilities of F lenses FAJ: Removes aperture ring from capabilities of FA lenses DA: Same capabilities as FAJ, but with reduced imaging circle for digital cameras with APS-C sized sensor DA L: Same capabilities as DA lenses, Lighter construction D FA: Same capabilities as FA lenses, usable on both film and digital cameras Features AL: Aspherical elements ED: Extra-low dispersion glass elements SMC: Super multi coating lens coating HD: Newer “high grade” multi-layer lens coating PZ: Power Zoom SDM: Auto Focus Type: Supersonic Drive Motor IF: Internal focussing WR: Weather Resistant (when matched with weather resistant body) AW: All Weather (again when matched with WR body; it’s unclear how if at all this differs from the above) ★: High performance, including weather and dust sealing Limited: High quality, compact design (primes) Macro: 1:1 magnification XS: Extra slim, even more compact than Limited
Sony/Minolta Lenses
Sony lenses, previously Minolta lenses, have similar features to Nikon and Canon. Their notation is as follows:
XYZmm: Focal length 1:x. y: Maximum aperture
ED: Extra-low dispersion glass elements SWD: Auto Focus Type: Supersonic Wave Drive Motor N: Version of lens (II = v2, III = v3, etc. )
XYZmm: Focal length 1:x. y: Maximum aperture
K, M: Manual Focus, Manual/Aperture priority metering AF: Early AF system with AF motor and electronics in lens that works only with ME-F body. A: Manual Focus, supports Shutter priority and Program exposure metering F: Adds Auto Focus to capabilities of A lenses FA: Adds ability to communicate MTF to body to capabilities of F lenses FAJ: Removes aperture ring from capabilities of FA lenses DA: Same capabilities as FAJ, but with reduced imaging circle for digital cameras with APS-C sized sensor DA L: Same capabilities as DA lenses, Lighter construction D FA: Same capabilities as FA lenses, usable on both film and digital cameras
AL: Aspherical elements ED: Extra-low dispersion glass elements SMC: Super multi coating lens coating HD: Newer “high grade” multi-layer lens coating PZ: Power Zoom SDM: Auto Focus Type: Supersonic Drive Motor IF: Internal focussing WR: Weather Resistant (when matched with weather resistant body) AW: All Weather (again when matched with WR body; it’s unclear how if at all this differs from the above) ★: High performance, including weather and dust sealing Limited: High quality, compact design (primes) Macro: 1:1 magnification XS: Extra slim, even more compact than Limited
Common XYZ/x. y: Focal length/Maximum Aperture Lens Mount Type Alpha: α Type Mount E: E Type Mount Focusing System SSM: In-Lens Super-sonic Motor SAM: In-Lens Micro Motor Features G: Gold Series (highest quality) (D): Distance Encoding (supports ADI feature of some Sony bodies) DT: Digital Technology (optimized for digital cameras) APO: Apochromatic correction using AD elements HS-APO: High-Speed APO AD: Anomalous Dispersion OSS: Optical Steady Shot (E-mount only) T*: High-performance Coating M: 1:1 magnification Z: optical engineering by Carl Zeiss
Examples
XYZ/x. y: Focal length/Maximum Aperture
Alpha: α Type Mount E: E Type Mount
SSM: In-Lens Super-sonic Motor SAM: In-Lens Micro Motor
G: Gold Series (highest quality) (D): Distance Encoding (supports ADI feature of some Sony bodies) DT: Digital Technology (optimized for digital cameras) APO: Apochromatic correction using AD elements HS-APO: High-Speed APO AD: Anomalous Dispersion OSS: Optical Steady Shot (E-mount only) T*: High-performance Coating M: 1:1 magnification Z: optical engineering by Carl Zeiss
HS-APO: High-Speed APO
Sony Alpha 70-200/2. 8 G Sony Alpha 28-75/2. 8 SAM Sony Alpha DT 18-250/3. 5-6. 3 Sony E 18-200/3. 5-6. 3 OSS Sony Alpha 100/2. 8 Macro
Off-Brand Lenses
Many off-brand lens manufacturers make lenses that fit many types of bodies, including Canon, Nikon, etc.
Sigma Lenses
Sigma lenses use the following terms to indicate features of each lens. They differ slightly in how they denote aperture:
Common XYZmm: Focal length Fx. y: Maximum aperture Compatible Body Brands Sigma Nikon Canon Minolta/Sony Pentax Kodak (extremely limited) Fujifilm Olympus (limited) Panasonic (very limited) Leica (very limited) Features HSM: Hyper-Sonic Motor ASP: Aspherical lens element APO: Aphochromatic (low-dispersion) lens element OS: Optical Stabilizer RF: Rear focusing IF: Inner focusing CONV: Teleconverter compatible (APO Teleconverter EX), not usually part of the lens name but mentioned in the product description EX: Professional lens body finishing and construction DG: Supports full-frame cameras (newer lenses only, implicit on older models) DC: Supports cropped-frame cameras (lightweight construction, smaller image circle) DN: For mirrorless cameras Macro: close focusing, but not necessarily 1:1 magnification
Examples
XYZmm: Focal length Fx. y: Maximum aperture
Sigma Nikon Canon Minolta/Sony Pentax Kodak (extremely limited) Fujifilm Olympus (limited) Panasonic (very limited) Leica (very limited)
HSM: Hyper-Sonic Motor ASP: Aspherical lens element APO: Aphochromatic (low-dispersion) lens element OS: Optical Stabilizer RF: Rear focusing IF: Inner focusing CONV: Teleconverter compatible (APO Teleconverter EX), not usually part of the lens name but mentioned in the product description EX: Professional lens body finishing and construction DG: Supports full-frame cameras (newer lenses only, implicit on older models) DC: Supports cropped-frame cameras (lightweight construction, smaller image circle) DN: For mirrorless cameras Macro: close focusing, but not necessarily 1:1 magnification
Sigma 18-250mm f/3. 5-6. 3 DC OS HSM Sigma 150-500mm f/5-6. 3 DG OS HSM Sigma 50mm f/1. 4 EX DG HSM Sigma 105mm f/2. 8 EX DG Macro
Tamron Lenses
Tamron lenses use the following terms to indicate features of each lens. Tamron offers a considerable degree of functional features and lens types, particularly lens types that affect chromatic aberration:
Common XYZmm: Focal length F/x. y: Maximum aperture AF: Auto-Focus Compatible Body Brands Nikon Canon Minolta/Sony Pentax Features Lens Elements XR: Extra Refractive Index Glass (lighter, smaller lenses) LD: Low Dispersion (chromatic aberration reduction) XLD: Extra Low Dispersion (advanced chromatic aberration reduction) ASL: Aspherical (improved focal plane convergence) LAH: LD + ASL hybrid lens element AD: Anomalous Dispersion (improved control over chromatic aberration) ADH: AD + ASL hybrid lens element HID: High Index, High Dispersion Glass (minimizes lateral chromatic aberration) Functional Features VC: Vibration Compensation USD: Ultrasonic Silent Drive SP: Super Performance (professional line) IF: Internal Focusing System Di: Digitally Integrated (optimized for use with full-frame digital cameras) Di-II: Digitally Integrated (optimized for use with APS-C digital cameras) ZL: Zoom Lock (prevents undesired zoom lens barrel extension) A/M: Auto-focus/Manual-focus Switch Mechanism FEC: Filter Effect Control (controls filter direction when lens hood attached, i. e. for Polarizing filters) 1:1 Macro: 1:1 Magnification
Examples
XYZmm: Focal length F/x. y: Maximum aperture AF: Auto-Focus
Nikon Canon Minolta/Sony Pentax
Lens Elements XR: Extra Refractive Index Glass (lighter, smaller lenses) LD: Low Dispersion (chromatic aberration reduction) XLD: Extra Low Dispersion (advanced chromatic aberration reduction) ASL: Aspherical (improved focal plane convergence) LAH: LD + ASL hybrid lens element AD: Anomalous Dispersion (improved control over chromatic aberration) ADH: AD + ASL hybrid lens element HID: High Index, High Dispersion Glass (minimizes lateral chromatic aberration) Functional Features VC: Vibration Compensation USD: Ultrasonic Silent Drive SP: Super Performance (professional line) IF: Internal Focusing System Di: Digitally Integrated (optimized for use with full-frame digital cameras) Di-II: Digitally Integrated (optimized for use with APS-C digital cameras) ZL: Zoom Lock (prevents undesired zoom lens barrel extension) A/M: Auto-focus/Manual-focus Switch Mechanism FEC: Filter Effect Control (controls filter direction when lens hood attached, i. e. for Polarizing filters) 1:1 Macro: 1:1 Magnification
XR: Extra Refractive Index Glass (lighter, smaller lenses) LD: Low Dispersion (chromatic aberration reduction) XLD: Extra Low Dispersion (advanced chromatic aberration reduction) ASL: Aspherical (improved focal plane convergence) LAH: LD + ASL hybrid lens element AD: Anomalous Dispersion (improved control over chromatic aberration) ADH: AD + ASL hybrid lens element HID: High Index, High Dispersion Glass (minimizes lateral chromatic aberration)
VC: Vibration Compensation USD: Ultrasonic Silent Drive SP: Super Performance (professional line) IF: Internal Focusing System Di: Digitally Integrated (optimized for use with full-frame digital cameras) Di-II: Digitally Integrated (optimized for use with APS-C digital cameras) ZL: Zoom Lock (prevents undesired zoom lens barrel extension) A/M: Auto-focus/Manual-focus Switch Mechanism FEC: Filter Effect Control (controls filter direction when lens hood attached, i. e. for Polarizing filters) 1:1 Macro: 1:1 Magnification
Tamron SP AF17-35MM F/2. 8-4 Di LD Aspherical (IF) Tamron AF18-200mm F/3. 5-6. 3 XR Di II LD Aspherical (IF) Tamron SP AF180mm F/3. 5 Di LD (IF) 1:1 Macro
Tokina Lenses
Tokina lenses use the following terms to indicate features of each lens:
Common VW~XYZmm: Focal length f/x. y: Maximum aperture AF: Auto-Focus Compatible Body Brands Nikon Canon Minolta/Sony Pentax Features AT-X Pro professional line (primes and constant aperture zooms) AT-X consumer line (variable aperture zooms) AS: Aspherical Optics F&R: Advanced Aspherical Optics SD: Super Low Dispersion HLD: High-Refraction, Low Dispersion MC: Multi-Coating FE: Floating Element System IF: Internal Focus System IRF: Internal Rear Focus System FC: Focus Clutch Mechanism (allows switching between auto & manual focus) One Touch FC: One-Touch Focus Clutch Mechanism FX: Full frame DX: Digital (cropped frame)
Samyang Lenses
Samyang (also sold as Pro-Optic, Rokinon, Bower) lenses use the following terms to indicate features of each lens:
VW~XYZmm: Focal length f/x. y: Maximum aperture AF: Auto-Focus
Nikon Canon Minolta/Sony Pentax
AT-X Pro professional line (primes and constant aperture zooms) AT-X consumer line (variable aperture zooms) AS: Aspherical Optics F&R: Advanced Aspherical Optics SD: Super Low Dispersion HLD: High-Refraction, Low Dispersion MC: Multi-Coating FE: Floating Element System IF: Internal Focus System IRF: Internal Rear Focus System FC: Focus Clutch Mechanism (allows switching between auto & manual focus) One Touch FC: One-Touch Focus Clutch Mechanism FX: Full frame DX: Digital (cropped frame)
Common XYZ mm: Focal length f/x. y: Maximum aperture Compatible Body Brands Nikon Canon Minolta/Sony Pentax/Samsung Olympus Panasonic Features AE: contains electronic chip to allow Automatic Exposure and iTTL flash metering on a Nikon body AS: contains Aspherical element(s) Aspherical: contains Aspherical element(s) ED: contains extra-low dispersion element(s) IF: Internal Focusing MC: Multi Coating UMC: Ultra Multi Coating MFT: designed for Micro Four Thirds systems CS VG10 – custom design for Sony Nex-VG10 Preset: Aperture preset (so you can quickly flick aperture ring between maximum aperture for focusing and desired aperture for shooting; there’s no aperture linkage on a preset lens) Mirror: a mirror lens
Examples
XYZ mm: Focal length f/x. y: Maximum aperture
Nikon Canon Minolta/Sony Pentax/Samsung Olympus Panasonic
AE: contains electronic chip to allow Automatic Exposure and iTTL flash metering on a Nikon body AS: contains Aspherical element(s) Aspherical: contains Aspherical element(s) ED: contains extra-low dispersion element(s) IF: Internal Focusing MC: Multi Coating UMC: Ultra Multi Coating MFT: designed for Micro Four Thirds systems CS VG10 – custom design for Sony Nex-VG10 Preset: Aperture preset (so you can quickly flick aperture ring between maximum aperture for focusing and desired aperture for shooting; there’s no aperture linkage on a preset lens) Mirror: a mirror lens
Samyang AE 14 mm f/2. 8 ED AS IF UMC Samyang 35 mm f/1. 4 AS UMC Pro-Optic AE 85 mm f/1. 4 Aspherical IF
Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.
Lenses only for reduced frame DSLRs
Most low to mid range DSLRs have a sensor that is smaller than a 35mm film frame – sometimes called “reduced frame” or “cropped sensor”. So using a “full frame” lens will mean lots of extra light around the sensor that isn’t used. You can makes lenses smaller and lighter by reducing the projected image size to fit the sensor size. However using these lenses on a full frame camera would result in the corners of the image being dark – and mostly these lenses won’t fit on a full frame camera.
The “less than full frame” codes are:
Canon: EF-S (EF for full frame) Nikon: DX (FX for full frame) Pentax: DA (FA or D FA for full frame) Sigma: DC (DG for full frame) Sony/Minolta: DT Tamron: Di II (Di for full frame)
Image Stabilisation/Vibration Reduction
Image Stabilisation is also called Optical Stabilisation, Optical Image Stabilisation, Optical Steady Shot, Vibration Compensation and Vibration Reduction. Does what it says on the tin basically. (Although note that some DSLR bodies have a form of vibration reduction in the body and so don’t need it in the lens).
Canon: IS Nikon: VR Panasonic: OIS Sigma: OS Sony/Minolta: OSS Tamron: VC
Fast and Quiet Focussing Motors
The focussing motors in some lower end lenses can be quite noisy. The higher end lenses are able to focus more quickly (the movements can be more accurately controlled) and are quieter and use less battery. The acronym for it usually includes “Sonic”:
Canon: USM Ultrasonic Motor Nikon: SWM Silent Wave Motor Olympus/Zuiko: SWD Supersonic Wave Drive Pentax: SDM Supersonic Drive Motor Sigma: HSM Hyper-Sonic Motor Sony/Minolta: SSM Super-Sonic Motor Tamron: USD Ultrasonic Silent Drive
Lens Features
There are a variety of lens features to reduce chromatic abberations (where different colours don’t exactly converge) and other imperfections in lens performance. In particular
aspherical lens elements have a more complex surface profile that can reduce or eliminate spherical aberration and also reduce other optical aberrations compared to a simple lens. low dispersion glass means that there is a relatively small difference in the amount different colours bend while going through the glass (technically the refractive index does not vary so much with wavelength), which reduces chromatic aberration. apochromatic lens elements are very good at reducing chromatic aberration – they are generally made up of three different materials stuck together. Canon: DO Diffractive Optics Nikon: ED Extra-low Dispersion Glass, ASP Aspherical Lens Element Olympus/Zuiko: ED Extra-low dispersion glass Pentax: ED Extra-low dispersion glass, AL Aspherical Lens Element Sigma: ASP Aspherical lens element, APO Aphochromatic (low-dispersion) lens element Sony/Minolta: AD Anomalous Dispersion, APO Apochromatic correction using AD elements, HS-APOHigh-Speed APO Tamron: Aspherical or ASL aspherical lens element, AD Anomalous Dispersion, ADH AD + ASL hybrid lens element, HID High Index, High Dispersion Glass, LD Low Dispersion, LAH LD + ASL hybrid lens element, XLD Extra Low Dispersion, XR Extra Refractive Index Glass Tokina: AS Aspherical lens element, F&R Advanced Aspherical lens element, HLD High-Refraction, Low Dispersion, SD Super Low Dispersion
Lens Coatings
There are a variety of lens coatings used to reduce internal reflections and other possible problems. Internal reflections can end up producing ghost images or adding to lens flare. Not all lens manufacturers specify the lens coatings they use.
Nikon: NIC Nikon Integrated Coating, SIC Super Integrated Coating Pentax: SMC Super Multi Coating Sony/Minolta: T High-performance Coating Tokina: MC Multi-Coating Yashica: DSB Single-Coating, ML (later MC) Multi-Layer (later Multi-coating)
Macro
Macro lenses can focus very close to the end of the lens, providing (at least) a 1:1 ratio between the size of the object and the size of the image on the sensor. In plain english, you can take very close up shots of flowers, insects and so on. They are just called Macro (or occasionally Micro), making life easy for once.
Focusing
This includes Internal/Inner Focusing (IF) and (Internal) Rear Focusing (RF or IRF). Both of these reduce the number of individual lenses moving inside the lens. They also mean that the front of the lens will not move in or out, or rotate, during focusing. The lack of rotation can be important if, say, you have a circular polarizing filter, or a graded ND filter fitted to the lens. And the front not moving in or out can be important if the lens is very close to the subject.
High End Lenses
Some manufacturers have a code to indicate their high end lenses:
Canon: L Luxury Pentax: * and Limited Sigma: EX Professional EXternal lens body finishing Sony: G Gold Series Tamron: SP Super Performance
Miscellaneous
Other codes might indicate the mount type (which will indicate whether it will fit your body), whether it will work with a Teleconverter or whether the lens needs the camera body to provide the motor for auto-focussing.
Note that I’m not an expert at this and am happy to integrate clarifications left in comments.
