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Lens FAQ: What Does a Lens Name Mean and Why are Some Lenses White?

What’s in a lens name? Why are some lenses white and some “decorated” with a red ring? Unravel the “secret code” on your lens in this article.

- Unravelling a lens name
- Red rings and green rings
- White lenses
- More about the different parts of a lens name


What’s in a lens name?

The very first thing that helps us differentiate one lens from another is its name.

Most lenses have the lens name printed on the front of the lens, although on some lenses, they may be printed elsewhere such as on the top of the lens barrel or near the mount.

The string of numbers and symbols on the lens may look confusing, but they mostly follow the same format:

A) Mount/Lens series
1: Lens series (Can be EF, EF-S, EF-M, TS-E, MP-E)

B) Focal length 
2: Focal length range (full-frame equivalent)

C) Maximum aperture range
3: Maximum aperture value/aperture range

D) Type of lens
4: Indicates a professional grade (L-series) lens
5: Indicates built-in image stabilisation
6: Lens generation number (Indicates new version of existing lens)
7: Type of AF motor (Can also be ‘STM’)

Other information you might also see in D):
- “Macro” (e.g. RF35mm f/1.8 Macro IS STM): Indicates a lens capable of at least 0.5x magnification
- “Fisheye” (e.g. EF8-15mm f/4L Fisheye USM): Indicates a special kind of ultra-wide-angle lens. More information here.

Click the links above to read more about each detail.


Red rings, green rings: Not just for decoration

Lenses have status symbols too! A red ring around the lens barrel indicates that the lens is an L-series lens. ‘L’ stands for ‘Luxury’, but L-series lenses are more than just that: they are built to provide reliability, durability, and the highest possible image quality, meeting the needs of professional users who earn a living with their gear.

This includes:
- Weather sealing: Dust and droplet-resistant design for better durability in challenging weather conditions.
- Higher quality optics: Special glass and coatings correct lens aberrations, ghosting, and flaring and ensure the best optical performance.

A green ring around the lens barrel indicates that the lens is equipped with Diffractive Optics, or DO lens elements. DO lens elements are a special type of glass that makes use of light diffraction to reduce chromatic aberrations, and using them helps to make telephoto lenses lighter.

Two much beloved examples are:
- EF70-300mm f/4.5-5.6 DO IS USM
- EF400mm f/4 DO IS II USM

Know this: Some lenses use DO lens elements but don’t have the green ring, such as the RF600mm f/11 IS STM and RF800mm f/11 IS STM.


What’s so special about white lenses?

If you see a white lens, it is probably an L-series telephoto zoom or super telephoto lens. These lenses are mainly used in sports, wildlife, and landscape photography, which often involve shooting for long hours under the hot sun. The highly reflective white heat shield coating protects against infrared rays in sunlight and helps to prevent heat from building up inside the lens, ensuring stable image quality.

Learn more about the story behind Canon’s white lenses in this article


More about the details in a lens name

1. Lens series

Currently, there are six existing lens series. Four are autofocus lens series:
i) RF: RF mount, designed for the EOS R mirrorless camera system.
ii) EF: EF mount, designed for full-frame DSLR cameras.
iii) EF-S: Derived from the EF mount; but designed for DSLR cameras with the smaller APS-C format image sensor.
iv) EF-M:  Another derivative of the EF mount, designed for use with the small and light EOS M mirrorless camera series.

The remaining two lens series are special manual focus lenses that use the EF mount:
v) TS-E: Tilt-shift lenses
vi) MP-E: MP stands for “Macro Photo”. It refers to the MP-E65mm f/2.8 1-5x Macro Photo, a special macro lens that supports up to 5x magnification

2. Focal length range (full-frame equivalent)

This indicates the angle of view that the lens provides. When the lens is mounted on a camera with an APS-C image sensor, the effective focal length is 1.6x the number stated. For example, the angles of view available on the EF-M15-45mm is equivalent to 24-72mm on a full-frame camera.

On some lenses, the focal length is also clearly indicated on the top of the lens barrel for easier identification.

Also see:
Professional Composition Techniques (3): Making Good Use of Lenses

3. Maximum aperture value
This indicates the widest that the hole in your lens can be opened (= the aperture diameter). It is usually expressed as an f-number (also known as ‘focal ratio’). 

On a variable aperture zoom lens, it is shown as a range of f-numbers. The smaller f-number is the maximum aperture at the wide-angle end, whereas the larger f-number is the maximum aperture at the telephoto end.

This tells us that on the RF24-105mm f/4-7.1 IS STM, the maximum aperture is f/4 at the 24mm wide-angle end, and f/7.1 at the 105mm telephoto end.

How the maximum aperture affects your shots 

When shooting in dim or dark conditions, a large aperture (“fast”) lens can take in more light, letting you shoot with a faster shutter speed and lower ISO speed. On mirrorless cameras and during Live View shooting on DSLR cameras, more light reaching the image sensor also helps AF performance in low light. 

As aperture is related to the depth of field, a larger maximum aperture also means more intense bokeh, which is why fast lenses are often favoured for portraiture.

Also seeCan A Fast Lens Really Make It Easier To See Through The Viewfinder?

Know this: The maximum aperture is sometimes written as a ratio, e.g. “1:4”

In other words, this is the inverse of the f-number. It is simply another way to indicate the maximum aperture.

Find out more about aperture in:
[Lesson 3] Learning about Aperture

4. L-series lenses
See Red rings, green rings: Not just for decoration

5. IS: Built-in image stabilisation

“IS” stands for “Image Stabilizer. In-lens IS is also known as Optical IS, and it detects camera shake and moves the corrective optics to compensate, resulting in sharper images even when you are shooting handheld.

While the image stabilisation effect depends on the scene and the lens, recent lenses can achieve as much as up to 5 shutter speed stops’ equivalent image stabilisation or more. Some RF lenses also support Coordinated Control IS, which works with the In-Body IS on compatible cameras to achieve even stronger image stabilisation effects.

6. Lens generation number

When a new lens has the same mount, focal length(s), aperture, IS or non-IS status, L-lens status, and motor as an existing model, it is considered a new generation of the lens and will carry a generation number in Roman numerals, e.g., EF400mm f/2.8L IS III USM.

First-generation lenses will not have the generation number indicated.

7. AF drive motor

There are two main types of motors use to drive the lens’ AF system.


Canon was the first camera manufacturer to successfully commercialise USM (Ultrasonic Motors), which converts ultrasonic vibrations to move the focusing group in a lens. They are known for their fast AF drive.

There are different types of USMs which you can read about here. The newest type is the Nano USM, which combines the seed of traditional USMs with the seamlessness, silence, and precision of STMs.


Stepping motors (STMs) debuted in 2012. They are known to have smoother, quieter AF drive than the older type of USMs, making them ideal for video. 

Read more about USM and STM technologies here



In the next article, we explore the different switches and controls you may find on your lens barrel.

To learn more about lenses and how to use them, check out:
In Focus: Lens Basics


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