Lenses // What do all those letters & numbers mean?

It can be pretty daunting to browse lenses online. Let  alone try to choose one! All those letters and numbers can just look like a huge, confusing jumble of techno babble. So here’s some info I figured out in these past couple years. Now, when I look at lenses, I know exactly what they’re talking about!

Letters ::

Here are some letters you will see often:


EF-S – The name of the mount which is the point of contact between the Canon body and lens (in modern Canon DSLRs) is called EF-S. This mount on a lens is only compatible with Canon cameras produced after 2003 as this is the year the mount was introduced. The reverse of the EF-S is the Canon EF lens. According to Wikipedia: “The ‘S’ in EF-S stands for “short back focus”, which means that the rear element of the lens is closer to the image sensor than on regular 35 mm SLR cameras. The proximity of the rear element to the image sensor greatly enhances the possibilities for wide angle and very wide angle lenses, enabling them to be made smaller, lighter (containing less glass), faster (larger aperture) and less expensive.” For a list of Canon cameras which are compatible with EF-S lenses, check the Wiki entry here. There’s a great list.

EF – The EF lens mount is far older and more established than the above mentioned EF-S. It’s been around since 1987 and is the ‘standard lens mount’ for Canon cameras. ‘EF’ stands for ‘electro focus’ which means that focusing is controlled by a fine motor built within the lens. Now remember above I mentioned the EF-S lens which only came out in 2003? It’s important to note that EF lenses can be put on EF-S cameras (exe: a 500D), although the image will be cropped. So while I have just purchased that lovely new 24-105mm lens, what I’m seeing and photographing is not a true 24 or 105mm because my 7D isn’t a full frame camera. But of course, I don’t know the difference so I don’t really care yet. Now, an EF-S lens cannot go on an EF body. So if I still had that EF-S 18-55mm kit lens that came with my first camera, I wouldn’t be able to use it when I move up to a full-frame some day. Don’t panic! Because when you and I get to the caliber of those cameras, trust me, we probably won’t be using EF-S lenses anymore. None of my current lenses are EF-S and they’re not all particularly luxurious ones either.

IS “Image Stabilisation” is the ‘IS’ you will see in lens names. And boy does it make my world a happier place! Through the invention of a gyroscope and floating element inside the lens, IS minimises camera shake due to unsteady hands, especially at long focal lengths. You may notice that when you use a zoom lens without IS, the images come out blurry/shaky. It’s not easy to zoom way out there and keep a steady hand. So a lens with IS is particularly important with long lenses. Think about it: when is it the hardest to keep the camera still and steady? When you’re using a slow shutter speed, right? Well with IS lenses, you can go a specified amount of ‘stops’ slower than you would without it. So although my 24-105mm can only have a max aperture of f/4, I can use two stops down (slower) shutter speed than I would without IS which helps to compensate for a not-so-wide open aperture. Other brands have IS too.

USM – In lens lingo, USM means ‘ultrasonic motor’. Canon pioneered the ultrasonic motor in the 80’s.


AF-S and AF-D – As far as I can tell from my reading, Nikon, unlike Canon, haven’t changed the mounting ring on their lenses. AF-S lenses have a focusing motor in the lens. AF-D lenses do not and the focusing comes from the camera. The ‘d’ in AF-D stands for ‘distance’ and speaks of the lens being able to communicate information back to the camera about the light situation at a distance. The camera can then evaluate, compensate and expose correctly.

SWM – ‘Silent wave motor”. Nikon’s version of the USM technology above.

VR (Nikon) – “Vibration reduction” is Nikon’s version of Canon’s IS (see above)


HSM – “Hyper sonic motor” (See USM above)

OS – ‘optical stabilisation’ (see IS above)

EX — “Excellence”, professional series. Sigma’s equivalent to the coveted Canon L series.


Minolta cameras take Sony lenses

SSM (Minolta, Sony) – “Supersonic motor”. See USM above.

DT – “Digital Technology”, lenses for APS-C size sensors (what a DSLR is when it isn’t a full frame sensor)

G – “G” Series, Sony professional lenses.

SAM – “Smooth Autofocus Motor”, in-lens motor offered on some entry level lenses since 2009.


SDM (Pentax) – “Supersonic drive motor”. See USM above.

DA – these are the lenses for digital cameras

FA – last of the pre-digital generation. Will only work with 35mm film cameras

D-FA –  35mm film lens, but are also updated to work better with APS-C sensors (digital)


USD (Tamron) – “Ultrasonic silent drive”. See USM above.

SP — ‘Super Performance’, professional lenses

IF — ‘Internal Focus’

LD — “Low Dispersion” elements

XR — Extra Refractive Index glass

VC — “Vibration Compensation” — in lens image stabilisation (see IS above in the Canon section)

USD — Ultrasonic Silent Drive

Numbers ::

Here’s the fun part. The part that used to make me scratch my head the most. The numbers! When looking at a lens name, there will be two sets of numbers. One tells you the focal length and the other tells you of the aperture capabilities of the lens.


A prime or ‘fixed’ lens is one which doesn’t zoom in and out, but stays fixed at a certain length. Examples of how these look within the names of lenses are: “Canon 50mm f/1.4 USM”. The 50mm part means that the lens stays fixed at 50mm. Other popular ones are 24mm, 85mm or 200mm.


If the name of the lens has two numbers, that means it’s a zoom lens. For example: “18-200mm” means that when the lens is at it’s ‘shortest’ or ‘widest’, it’s an 18mm lens. When fully extended, ‘zoomed’ or ‘long’, it can go up to 200mm. And of course, it can cover anything in between.


The aperture of a lens is measured in f/stops. Remember, aperture is like how wide open the pupils of your eye are. The more wide open (the lower the number) the more light is let in. The higher the number, the more closed the aperture and the less light, thus requiring slower shutter speeds or higher ISOs to properly expose  your photos. Which isn’t ideal for indoors.

So on a prime ‘fixed’ lens, there will be one such number. Exe: 50mm f/1.4. The focal length is 50mm and the most wide open aperture you can get on that lens is 1.4. Canon makes a f/1.2 50mm lens but that’s about as wide open as you’re going to get without spending many thousands on a lens. So 1.4 is pretty good.


On a zoom lens, there’s usually an aperture range (two f/stop numbers) much like the two numbers to tell you the range of the focal length. On the lens which often comes with Canon cameras, the name looks like this: “Canon EF-S 18-200mm f3.5-5.6 IS Lens” 18-200mm is the focal length(s) and the aperture measurements are f/3.5 to f/5.6. Which means that when the lens is at it’s widest (or shortest), the min f/stop can be down to 3.5. When it’s zoomed all the way to 200mm, the min f/stop is f/5.6. Now, f/5.6 is really not a good aperture to ever be using indoors so I traded this lens for a more friendly zoom for weddings which brings me to my next point.

Some zoom lenses only have 1 f/stop in the name, even though it zooms in and out. Exe: “Canon 24-105mm f/4 IS”. This means that no matter what length I’m using this lens on, the aperture can remain at f/4. Which also means that I can set my manual settings and zoom in and out without the exposure of the photo being affected. Which isn’t true of the above mentioned kit lens.


Whew! What an epic post this was. Is anyone even still reading? :) It might just need to be one of those things you refer to when browsing for your next lens. But anyhow, hope it helped!

  • Thank you. This is helpful. It seems to be taking me a long time to understand lenses.

  • Joanne Thomas

    I think that Sony has not changed the mounting ring on their lenses as well. I have a lens I bought for my Nikon EM film camera over 30 years ago and it fits my latest and greatest Nikon camera. I love that I don’t have to buy new lenses every time I upgrade. I will have to get full frame lenses when I upgrade to the D700 however I can still use all my other lense–they just won’t shoot full frame. Likewise I can use the full frame lenses on all my other Nikon cameras it will not take full frame on those.

  • me me! i read to the end!!! it’s great to read photography tips and learn more of the lingo, especially to a hobbyist like me!!

  • Pamela

    Thanks for sharing!! I have lots to learn and your explanations and examples make it easy to understand and comprehend!

  • Simona

    Thank you so much for this article! I’ve been reviewing the Tamron lenses since some reviews state they are just as good as, if not better than some of the Canon lenses. However, it was extremely hard to tell what all the jargon meant, even after viewing their own website, I had no clue for example

    Tamron AF 28-75mm f/2.8 SP XR ZL Di LD Aspherical (IF) for Canon Digital SLR Cameras

    Now I can use your lens lingo to decipher. :-)

  • Simona

    Question. What does the smaller number on the lens mean

    I recently received the 75 – 300 as a gift and it lists

    its has a the macro symbol and next to it reads. 1.5m/4.9ft

    Does that represent the maximum focusing distance to obtain a clear macro picture?

  • Wow, I can tell you put a lot of work into this post and I would like to sincerely thank you. It takes a lot of work putting all that together and I want you to know that your readers really do appreciate it!

  • Marta

    Wow! This a very useful explanation… I love it…
    Thanks for making my life easier!

  • Nikki

    Thanks for listing all these abbreviations and numbers! Nice to see the different brands together. By the way, FA lenses can be used on Pentax dslrs (at least no one told my camera it couldn’t–they work well, and the aperture control and metering function too.)

  • Laura

    Thank you so much for posting this! It was very easy to read and understand. I’d love to hear what some of the other letters mean sometime. For example, take this lens:

    Nikon 70-300mm f/4.5-5.6G ED IF AF-S VR

    What do ED and IF stand for??

  • I just reread this post and I have two questions:
    1. the USM for Canon – you told what it is, but is it really important? Does it make photos that much better?
    2. Why would EF-S lenses not work on a full-frame camera? Are full frame cameras produced after 2003 not using the whatever s thingy? I kinda lost that. Does it have to do with exactly what is a full frame?

  • Peter Pechacek

    @ Laura
    The ED stands for “Extra Low Dispersion”, which means there are specially shaped pieces of glass inside that help reduce chromatic aberrations which are bits of colored fringing in the image.

    The IF is for “internal focus” which means that the lens uses lens elements internally to adjust the focus compared to some lenses using the front piece of glass as the focus lens. It’s usually a good thing to have IF.

  • Peter Pechacek

    @ Texan Mama
    1. The USM is important because lenses that have that feature have a quieter or silent focusing motor. This can be important for quiet events like wedding ceremonies or even nature photography so you do not scare the animals.

    2. Because the EF-S lenses are built specifically for the smaller sensor cameras, the rear housing “sits” closer to the sensor than an EF lens would for a full frame cam. If you were to use an EF-S lens on a full frame camera, the rear housing would be in the way of the mirror that moves.

    You could modify some of the EF-S lenses to not interfere with the mirror or you could attach an extension tube; but then there is the other issue of vignetting (dark edges) in your image and not being able to focus to infinity.

  • Peter Pechacek

    @ Texan Mama
    Also USM lenses are faster at focusing.

  • Eric81

    Thanks for keeping it neat and simple.

  • Tina

    Thank you.  This is a very helpful articles as are all your others.  Thanks for taking the time to do these.

  • Gerty Mitchell

    oh my this is so helpful! and in words I can understand!!! I am still at a loss however as to what the focal length means. I get the the numbers mean the zoom OUT and zoom IN values, but how do I use that information when I choose which lens to buy. Any tips?

  • elizabethhalford

    Hi Gerty! Come back for tomorrow’s blog post all about focal length ;)

  • Kay

    thank you so much I was wondering what all those letters mean , then this post came up to my google search~ This is so helpful, thanks again.

  • Mpres

    This is so helpful! Just got a new dslr and was getting so confused looking at potential lenses! Thanks!

  • emris

    Thank you so much!

  • You are an amazing inspiration!

  • Karthick

    Very nice.. have been looking for this info for a long time now

  • suzanne L Kish

    I enjoyed your blog. Found it on Pineinterest.

  • Michelle

    Thank you sooo much!!! So helpful!

  • Dalila

    This was very helpful!! Thank you!! :)

  • Kenyarta Hart

    Thank you i have been shotting for a while most of what you wrote i knew but i was a little confused about the difeference between the EF-S and EF series lenses but now i am not. And yes ppl are still reading this blog it is very informative and a need to know for photographers looking to shoot M. Again, thank you for this information.

  • Kenyarta Hart

    thank you

  • Confido

    Hi. Does the old Minolta 70-210mm beercan qualify as a 1f/stop lens?

  • Z

    Thanks so much. Very very helpful.

  • Giles

    I know this is an old blog, but I’ve just been looking at different cameras… already worked out I wanted to get one that takes different lenses, so I can specifically get a macro lens to go with it, but hadn’t got a clue what all the numbers meant, what with canon having so many choices of lenses. Your description has certainly helped me get a better understanding and now I know what I’m looking at.

  • Beginner Photographer 101

    so a nikon 18-105mm f/3.5-5.6 ED is a lens that zooms anywhere from 18-105mm and aperature varies depending on zoom anywhere from 3.5 f/stops to 5.6 f/stops. Right?

    Now what does the ED stand for?

  • Neamatullah Neamat

    Thank you very much.

  • Beanz

    Super helpful. Thanks!

  • Ryan Amm

    Thank you, now i have some understanding for how the camera stuff works