Before I get into the nitty-gritty of why Lens Abbreviations are all different, let’s look at the commonalities. You have to mainly look at three common terms that describe SLR lenses. These three terms are easy to understand, and they mainly relate to creative and performance functions. These three terms are Focal Length, Maximum Aperture, and AF/MF.
Focal length: The scope of the scene captured (for example, a 16–35mm is a lens which covers an area of 16mm [relatively wide] and zooms to 35mm).
Maximum aperture: The maximum size of the hole that lets light into the camera (e.g. f/1.8 or f3.5–5.6). If a lens has only one number, then it has only one maximum aperture. However, if it has two numbers then there are multiple maximum apertures depending on the focal length of the lens. Lower aperture number means that the hole is larger and more light goes into the camera.
AF/MF: Auto Focus and Manual Focus. Most lenses have a button that lets you switch between the two focus modes.
Understanding the Format Abbreviations of Canon lenses
Canon has a very wide array of lenses for their EOS cameras. Also, third-party lenses from Sigma, Tamron, and Tokina add a lot of options in the market. Now let me tell you about the abbreviations used on Canon lenses and what they mean.
EF: EF stands for Electronic Focus. These lenses were introduced in 1987. They are designed to work with every EOS camera. They cover the 35 mm full-frame segment.
EF-S: EF-S is similar to the EF lenses, the difference being that the EF-S is designed to fit perfectly in Canon cameras like the Canon 700D. They cannot be attached to cameras with full frames like the 5D. Since the full frames have a larger mirror, these EF-S lenses do not fit with these cameras. There is a protective pin attached to the EF-S that prevent you from mounting it.
EF-M: These are a new series of lenses that have been manufactured for the entire Mirrorless EOS M camera series. These are also similar to the EF-S and have been premeditated for APS-C sensor cameras. EF-M lenses can only be used with EOS M series cameras. But do not worry if you have an EOS M series camera, thinking that you will be limited to EF-M lenses only. You can easily attach EF and EF-S lenses with the appropriate mount to any EOS M series camera.
FD: These are old-school Canon lenses during the film era. They were all manual focus lenses. Since these lenses did not support autofocus, Canon replaced them with the EF mount lens system. The FD lenses are no longer manufactured. Still, a lot of film photographers use the FD lenses. Interestingly, you can even use these FD lenses with your EOS EF cameras with the proper adapters.
FDn: These lenses are virtually FD lenses, the only difference being that the FDn lenses do not have any coating on the front of the lens.
FL: These lenses are also very similar to the FD lenses with the same type of mount. But they cannot meter at the highest aperture.
Understanding Class and Technology
L: The L in the Canon L series lenses stands for Luxury. These are the top-of-the-line lenses manufactured by Canon, best fit for professional use. They have the highest quality and unconventional optical formulas. Canon builds them to the highest possible standards and includes composite glass parts in them.
Additionally, they usually have wide aperture settings and weather protection. They are priced high, as expected, but some lenses (24-105mm f/4L) are priced at a little over $1,100, which is considered quite reasonable for the quality. All L series lenses can be recognized by a red marker on the lens.
SSC: SSC stands for Super Spectra Coating. This technology was originally discovered in 1886 by a Lord Rayleigh. Later, Carl Zeiss enhanced the technology even further. Lens coatings were a game changer and made an impact even on impending optics. It ensures that reflections are at a minimum, and you can get as much contrast as possible. Since all modern-day lenses are coated with multiple layers, the SSC mark on lenses are not usually seen anymore except for old school lenses.
Roman Numerals: Roman numerals that you often see in Canon lenses denote which generation the lens is from. Take the two versions of Canon lenses with specifications 24-70mm and f/2.8L as an example: Canon EF 24-70mm f/2.8L USM or Canon EF 24-70mm f/2.8L II USM. If you look carefully you will notice the variance in the names is a one and two numbering in Roman numerals. This means that the latter is the fresher and restructured version.
USM: USM stands for UltraSonic Motor. The USM uses a focusing motor of Canon. It is fast and powerful yet quiet. These also allow override to manual mode. USM is seen in all types of lenses—from cheap prime lenses to even the L-class.
Micro USM: The Micro USM is like the younger brother of the USM. It is used in most Canon lenses. However, the key difference is unlike the USM, there is no override system for uninterrupted manual mode for focusing. The EF 50mm f/1.4 USM packs a Micro USM inside it. Notice how the name does not mention micro—this is because there are labels on USMs and Micro USMs as USM.
STM: STM stands for Stepper Motor. The STM is specially designed to decrease autofocus pulsations and unwanted backdrops at the time of recording. These days, it is quite common to find STM motors in cheap lenses from Canon. STM was first seen in the EF-M 22mm f/2 STMs. Nowadays, most of the EF-M lenses use Stepper Motors. Some EF-S lenses went through restructurings to include the STM motor. STM lenses have fly-by-wire technology. This means that whenever you are rotating the focus wheel, the elements do not move themselves but rather instructs the AF motor inside to mobilize.
AFD: A Canon Lens with a motor that focuses automatically. Compared to a USM, it is much slower-paced and noisy. Moreover, it doesn’t have an override for the manual focus in AFD lenses. Old school lenses usually have AFD motors. Lenses with no markings on them usually have either an AFD or a Micro Motor.
MM: Micro Motor is smaller than the AFD motor and is used in cheap Canon lenses. An example of MM is the EF-S 18-55mm f/3.5-5.6 IS II kit lens. Similar to the AFD, it doesn’t have an override for full-time manual mode. Additionally, it is brassier in operation compared to a USM. However, since the kit is light-weight and the internal motor is compact, this makes noise not much of an issue.
PZ: PZ means that the motor is out-and-out, which gives users the ability to adjust different focal lengths. The only EF lens I have seen to go with this lens is the 35-80mm f/4-5.6 PZ.
IS: IS stands for Image Stabilizer which mobilizes the lens’ optics to prevent movement made by the hand. This in turn provides shriller results when you are using a slower shutter speed.
Understanding some specialized Lens
Macro: Macro lenses have designation focuses that can zoom into short distances. This affords 1:1 magnification and is great for taking up-close and zoomed-in images.
Compact Macro: This is very similar to any regular macro lens. I have seen only one Compact Macro lens so far—the EF 50mm f/2.5 Compact Macro lens. There is a devoted converter, Canon Life-Size Converter EF, available for this lens. This converter upsurges the working distance and enables you to get magnifications with a ratio of 1:1.
MP-E: Similar to the Compact Macro lens, there is only a single lens with MP-E designation. It is called MP-E 62mm f/2.8 1-5x Macro lens. This lens gives you exceptional magnification. This lens can focus with magnifications beyond regular macro capabilities. The lens has only manual-focus and cannot focus everywhere. On the plus side, MP-E has 1:1/5:1 magnification.
TS-E: TS-E are lenses with which tilt-able variations can be made. These lenses are primarily used for portraits, landscapes, architecture photography, etc. These lenses do not usually have automatic focus. Also, they are quite exotic and expensive.
DO: DO stands for Diffractive Optics. The DO lenses have advanced glass parts that diffract light better than any regular glass. For this reason, DO lenses are usually smaller in size than any other lens having the same specifications. A popular lens from the DO series is the telephoto EF (400mm f/4 DO IS USM). The lens has of similar build quality to any L series lens, but instead of having a red ring, there is a green marker.
Softfocus: As the name Softfocus suggests, these lenses have an optical formula used to get milder results. These lenses were popular choices a long ago among photographers who wanted to capture portraits that concealed skin flaws and produced a “pensive” and radiant effect in films. Needless to say, these lenses have lost their popularity. These days you can achieve a soft-focus upshot with an editing software if you wish. The only EF lens I know of with Softfocus, is the 135mm f/2.8 with Softfocus.
I would advise that before opting for a lens for any camera, be it beginner's level or professional, you should know your priority of lens and for which purpose you need to use it for, whehther it wide-angle, macro, soft focus, etc., especially if you’re not buying multiple types of lenses in a single purchase. You generally can’t find the older version in stores, and so, there’s no way to make a mistake on that front, but you have to watch out in second-hand stores and in reviews, where you can run into models from various periods. Do look for best deals online, comparing the prices of the selected version for the best purchase.