Decoding DSLR Camera Lens Acronyms
Do these DSLR camera lens names confuse you?
- Canon EF 40mm f/2.8 STM
- Canon EF-S 15–85mm f/3.5–5.6 IS USM
- Canon EF 24mm f/1.4L II USM
- Nikon AF-S DX NIKKOR 55–300mm f/4.5–5.6G ED VR
- Sigma 150mm F2.8 EX DG OS HSM APO Macro
If you’ve studied the markings on your lens, you already know it’s littered with acronyms. It only gets worse as you dig deeper and realize that every lens vendor has created their own alphabet soup for the same meanings.
Even once you locate a definition, you’re flooded with words like aspherical, apochromatic, fluorite, nano crystal, ultrasonic, hypersonic, hyperzoom, extra-low dispersion and chromatic aberration.
The only aberration I see is the nonsense of such complexity! In this post, I’ll break down lens names and cover off the acronyms that I think matter most. I’ll also include links to a few useful glossaries and lens-locating resources.
Lens Listings
Before I get started, here are the official lenses offered by the most popular DSLR camera brands:
Additionally, third-party manufacturers produce lenses with mounts for multiple camera brands:
Lens Mount
Portion of lens name being discussed:
- Canon EF-S 15–85mm f/3.5–5.6 IS USM
- Canon EF 24mm f/1.4L II USM
- Nikon AF-S DX NIKKOR 55–300mm f/4.5–5.6G ED VR
- Sigma 150mm F2.8 EX DG OS HSM APO Macro
The most important acronym on any lens will be the one that tells you if it actually fits your camera or not. This relates directly to your camera brand, make and sensor size. Luckily, most people have cameras with cropped (APS-C) sensors and they can take all classic and modern “made-for-digital” lenses (same brand lenses or third-party lenses targeted for the camera brand).
If, however, you own a full-frame sensor camera (e.g. Canon EOS 5D Mark II), then you need to be more careful as it cannot take lenses made for smaller sensors.
UPDATE: I talk extensively about crop-factor in Episode 1 of “Back to Basics”, my new video tutorial series.
Lenses for Full-Frame and Cropped Sensor Cameras
Look for these acronyms to find lenses that work only on full-frame cameras (those with sensors that are the same size as 35mm film). Digital cameras with smaller sensors can also use these (i.e. these lenses create a larger image than the smaller sensor which is why it works).
- Canon: EF
- Nikon: FX
- Sony: Any lens without “DT”
- Pentax: D FA and FA
- Sigma: DG
- Tamron: Di
- Tokina: FX
Lenses Only for Cropped-Sensor Cameras
Look for these acronyms to find lenses built specifically for DSLR cameras with smaller sensors (referred to as an APS-C sensors). Since the sensor is smaller, the diameter of the lens barrel can be reduced. This makes the lens more lightweight and cheaper to manufacture. These do not work on full-frame cameras as the image produced would be smaller than the sensor (picture a huge black vignette).
- Canon: EF-S
- Nikon: DX
- Sony: DT
- Pentax: DA
- Sigma: DC
- Tamron: Di II
- Tokina: DX
Focal Length
Portion of lens name being discussed:
- Canon EF-S 15–85mm f/3.5–5.6 IS USM
- Canon EF 24mm f/1.4L II USM
- Nikon AF-S DX NIKKOR 55–300mm f/4.5–5.6G ED VR
- Sigma 150mm F2.8 EX DG OS HSM APO Macro
Technically, focal length is the distance in millimetres between where light from infinity is focused and the optical centre of the lens. In laymen terms, it determines how close or far you feel from the subject. The smaller the number, the wider the angle. The large the number, the more zoomed in you’ll be.
Luckily, there’s only a few common names for focal length ranges:
- Ultra-wide: 16mm or less
- Wide: 17–35mm
- Standard / Normal: 50mm (similar to human eye)
- Medium Telephoto: 70–85mm
- Telephoto: 135–300mm
- Super Telephoto: 400mm or greater
A lens name may have a single focal length value (e.g. 24mm) or a range (24–70mm). Those with a single focal length are called “prime” lenses while those with a range are called “zoom” lenses. Zoom lenses are convenient but prime lenses are often faster (i.e. let in more light), weigh less and cost less. To zoom with a prime lens, you just need to move your feet!
UPDATE: I also cover focal length and angle of view in Episode 1 of Learning DSLR: Back to Basics.
It’s important to note that the focal length of a lens is always provided as the “35mm equivalent” value. That means the number only relates to cameras with full-frame sensors. Most digital cameras, however, have sensors smaller than 35mm film (APS-C sensor size). You must do a conversion of the focal length to determine if a lens is actually wide, normal or telephoto.
Since the APS-C sensor is smaller than 35mm film, the camera uses only the the center portion of the image produced by the lens. It’s like cropping a photo in post-production. It’s similar to zooming in without actually changing the nature of the photo.
To know how a particular focal length will “feel” on your cropped-sensor camera, you need to apply a multiplier to the focal length value in the lens name (e.g. 50mm x 1.6 = 80mm).
The required multiplier varies by camera manufacturer:
- Nikon, Sony & Pentax: 1.5x multiplier
- Canon: 1.6px multiplier
For example, if you really wanted a normal (50mm) prime lens for your cropped-sensor camera, do division instead. 50mm divided by 1.6 (for Canon) is 31.25mm. The closest lenses you’ll find are 28mm and 35mm (which will feel like 44mm and 56mm respectively).
For Canon cropped-sensor owners wanting a normal lens, I suggest the Canon EF 28mm f/1.8 USM ($450) given the 35mm f/2 ($300) does not have an ultrasonic focusing motor (see below for more on that) and the 35mm f/1.4L ($1,370) is too expensive. If you buy a 50mm, it would work fine but you might find it tight. Personally, I like the 80–85mm feel of my Canon EF 50mm f/1.4 USM ($350).
Aperture
Portion of lens name being discussed:
- Canon EF-S 15–85mm f/3.5–5.6 IS USM
- Canon EF 24mm f/1.4L II USM
- Nikon AF-S DX NIKKOR 55–300mm f/4.5–5.6G ED VR
- Sigma 150mm F2.8 EX DG OS HSM APO Macro
Aperture is the opening created to allow light to enter a lens. It is varied by mechanical blades inside the lens. A lens’ maximum aperture is specified as part of its name (e.g. f/2.8). The minimum aperture is never specified (e.g. f/22 or f/32) but you can look it up.
UPDATE: I explain aperture in-depth in Episode 2 of Learning DSLR: Back to Basics
A smaller aperture value is better overall as it means the lens can let in more light when needed and it’s easier to blur the background for some selective focusing. The downside is it costs more to manufacture and typically weighs more than comparable lenses (larger pieces of glass).
Aperture values are tough to learn at first as they’re a ratio to focal length. It’s done this way for consistency across all lens focal lengths (f/2.8 in a 24mm lets is the same amount of light as f/2.8 in a 500mm lens). Since it’s a ratio, aperture values are expressed as fractions “f/2.8” or in ratio notation “1:2.8”.
Most kit zoom lenses have an aperture range in their name (e.g. f/3.5–5.6). The range means that the maximum aperture gets worse as you zoom in (less light reaches the sensor the more you zoom). Your camera must compensate with a slower shutter speed or a higher ISO setting. This is most noticeable during video capture as the image really does darken as you zoom in. Professional lenses typically have a constant aperture throughout the zoom range to overcome this shortcoming… but this will cost you (e.g. Canon 70–200mm f/4L or f/2.8L).
Also, don’t get fooled by the small steps in aperture values when the aperture values are small numbers (e.g. below f/4). Small jumps in those values have a big impact. Think of it as a percentage of change in those values. The difference between f/1.4 and f/2 is the same as f/16 and f/22. In both cases, the lower value lets in twice as much light as the higher value.
Premium Lens Characteristics
Portion of lens name being discussed:
- Canon EF 24mm f/1.4L II USM
- Sigma 150mm F2.8 EX DG OS HSM APO Macro
You’ll notice that lenses prices can vary widely, even for the same focal-length. Why is one Canon 50mm lens $99 and another $1459? The answer is found in the premium properties of the “professional” grade lenses.
Pro-grade lenses have many additional features that boost image quality and make the lens more robust, like weather sealing and metal barrels.
Here’s some of the premium features you may want in a lens:
- Aspherical (concentrates light more accurately)
- Extra-Low dispersion glass (reduces chromatic aberration)
- Apochromatic (reduces chromatic aberration)
- Internal focusing (faster focusing, no lens movement)
- Rear focusing (faster focusing, no lens movement)
- Weather sealing (more robust)
- Special coatings (improve image sharpness, avoid flares)
The definition of what is a premium or pro-grade property varies the most across lens manufacturers. Some summarize it with a single letter like Canon’s “L” designation, while others list each premium feature with its own acronym.
- Canon: “L” (Luxury) + red ring around the lens
- Nikon: “N” (Nano crystal coat) + gold ring around the lens
- Sony: “G” and “Carl Zeiss”
- Pentax: “DA Star”and “DA Limited”
For the other brands, it seems to me that there’s no single designation. They just tack on the alphabet soup of premium features such as ASP, APO, IF, etc. You’ll need to dig into their respective glossaries for more definitions.
Anti-Camera-Shake
Portion of lens name being discussed:
- Canon EF-S 15–85mm f/3.5–5.6 IS USM
- Nikon AF-S DX NIKKOR 55–300mm f/4.5–5.6G ED VR
One of the latest (and most expensive) additions to a lens is technology to reduce the effects of camera shake. They allow you to take a sharp photo with 1/8th to 1/16th less light (i.e. 3 to 4 stops of light). This is critical for interior shots without a flash.
To a find a lens with this feature, look for these acronyms:
- Canon: IS (Image Stabilization)
- Nikon: VR (Vibration Reduction)
- Sigma: OS (Optical Stabilization)
- Tamron: VC (Vibration Compensation)
- Tokina: Not available
Some camera manufacturers stabilize the sensor instead of putting the technology in the lens. This means every lens you buy benefits from the technology. Two such manufacturers are Sony and Pentax:
- Sony: Super SteadyShot
- Pentax: Shake Reduction
Lens Version
Portion of lens name being discussed:
- Canon EF 24mm f/1.4L II USM
On some lenses, you might see a roman numeral like “II” or “III”. This exists to tell you that a lens with exactly the same specifications, by the same vendor, existed prior to this lens. In my example, “II” is said as “Mark 2” and it means it’s the second generation Canon lens for 24mm f/1.4L. Typically a lens is updated to boost sharpness and auto-focus.
If you’re shopping for used lenses, be aware of this difference as it will have an impact on price. For example, compare prices on eBay the Canon EF 70–200mm f/2.8L IS USM vs. Canon EF 70–200mm f/2.8L IS II USM.
Ultrasonic Motor
Portion of lens name being discussed:
- Canon EF-S 15–85mm f/3.5–5.6 IS USM
- Canon EF 40mm f/2.8 STM
- Sigma 150mm F2.8 EX DG OS HSM APO Macro
If you want a quiet and fast auto-focusing lens, then an ultrasonic motor built right into the lens is a must. Older motors are noticeable louder and slower. Most new lenses have this feature so you don’t have to look too hard to find it.
Not all camera manufacturers state the focusing motor type in the lens name. Nikon, for example, doesn’t seem to include it.
Here’s the acronyms you’re looking for:
- Canon: USM (Ultra Sonic Motor)
- Canon: STM (Stepping Motor)
- Nikon: SWM (Silent Wave Motor)
- Sony: SSM (Super Sonic wave Motor)
- Pentax: SDM
- Sigma: HSM (Hypersonic Motor)
- Tamron: USD
- Tokina: DC
These lenses typically include the ability to manually focus your lens while it’s still in auto-focus (AF) mode. For Nikon, they have a dedicated acronym for this: “AF-S” instead of just “AF”.
Note for Canon owners: Canon uses the USM acronym to denote two types of ultrasonic motors. You want lenses that have Ring USM (not the cheaper micromotor version). Check the lens’ specifications to be sure.
UPDATE June 8, 2012: Canon’s new STM functionality provides quiet, smooth and continuous autofocus during video operation. The continuous autofocus will only work with the Canon T4i currently and cameras released after June 2012. That said, a more silent motor is always appreciated if it’s as fast as Ring USM.
Specialty Lenses
Sometimes a lens will include a designation to signal it’s a special type of lens. Three of the most common specialties are:
- Macro
- Fisheye
- Tilt-Shift
Macro
A macro lens allows you to get very close to your subject and represent small items as a major part of a photograph. The image on your sensor can be 1:1 or larger. Macro photography often involves flowers, insects and small collectable items but it can be anything.
Learn more about macro photography and see some examples of macro photography of Flickr.
To find a macro lens, just look for the word “Macro” in the lens name.
Fisheye
Most lenses render straight edges (e.g. horizon and buildings) as straight, even if it requires stretching the image in the corners. They are referred to as rectilinear lenses. A fisheye lens, however, permits distortion to occur at wide-angles and they’re referred to as curvilinear. Imagine a landscape photo that simulates the curvature of the earth on the horizon or a building interior that seems to fit entirely in a single photo.
Fisheye lenses can produce perfectly round 180-degree images (8–10mm on a full-frame camera) but can also fill the entire frame (10–15mm). Learn more about fisheye lenses and see some examples of fisheye photography on Flickr.
To find a fisheye lens, just look for the word “Fisheye” in the name.
Tilt-Shift
This expensive but very cool type of lens doesn’t zoom and doesn’t even auto-focus. What it has is the ability to change the plane of focus by pivoting relative to the image plane (tilt) and the ability to move in parallel to the image plan (shift). The tilt and shift is done with simple thumb screws.
The shift feature is popular in architectural photography as it allows you keep your camera level to the ground (which avoids converging vertical lines) while still allowing you to fit in a tall building (see this explained in detail here).
A popular use of the tilt feature is for selective focus (e.g. unnatural blurring of foreground and background which brings focus to one banded area of the photo). This is popular in contemporary wedding portraits but also with landscapes as it can make real-world scenes appear like miniatures.
Learn more about tilt-shift photography and see some examples of tilt-shift photography.
To find a tilt-shift lens, look for these special acronyms:
- Canon: TS-E (Tilt-Shift)
- Nikon: PC-E (Perspective Control)
Additional Resources
- Canon Lens Selector (by Canon, nice interface)
- LensHero (lens buying wizard)
- Lens Buying Guide by Vistek (a deep guide with lots of insights)
- Lens Acronym Glossary by Vistek (every acronym defined for Nikon, Canon, Tamron and Sigma)
- Nikon Lens Glossary (complete list but Nikon specific)
- LensDatabase (fastest way to list available lenses given a few criteria)
- DxOMark Lens Database (highly technical reviews with charts and graphs)
- Pixel Peeper (find photos taken with a particular camera and/or lens)
- myLensDB (find photos taken with a particular camera and/or lens)
Was this summary useful? What else do you find confusing when shopping for lenses or camera gear? Let me know!
