100mm and 50mm – What do all the letter mean?

This post is the fourth(? – I have lost count already) in a series about lenses.  For many first time DSLR users, the sheer variety of lenses can be daunting. Furthering the confusion is all the lenses that at first glance seem similar in some respects but vary widely in price.  In this post we will take a look at all those acronyms that follow the basic lens info and break it all down into clear and concise english.

To start we need an example lens and what better place to start than the lens that most first time DSLR buyers get with their camera, the kit lens.  Called the kit lens because you buy the lens and camera together as a kit.

Canon EF-S – Zoom lens – 18mm-55mm – f/3.5-5.6 IS

First the basics- this lens has a focal length range from 18mm to 55mm, about a 3x zoom. If you didn’t know that spend a few minutes reading my focal length lens post.  The aperture is variable from f/2.4 to f/5.6 and I have more information about that in my Aperture Explained post.  Now what is left?

Canon EF-S – Zoom lens – 18mm-55mm – f/3.5-5.6 IS

EF-S and IS

EF-S is the mount of the camera, the connection between the lens and the camera.  Canon has two major mount types: EF-S and EF.   EF lenses work on both full frame cameras like the very expensive 5D MII and crop sensor cameras like the Canon Rebels (e.g. T2i/500D). EF-S lenses only work on the crop sensor cameras.  Nikon equivalent designation for crop sensor cameras is DX, Sigma uses DC and Tamron uses Di-II.

IS is image stabilization – some lenses have tiny gyroscopes that help stabilize the lens, making it easier to get a crisp shot at slower shutter speeds. Remember that the general rule is your shutter speed should be faster than your focal length, meaning if you are shooting at 50mm your shutter speed needs to be above 1/50 of a second to avoid blurring your images.  Image stabilization allows you to break this rule, sometimes by 2-3 stops.  It does not freeze the action of moving objects, only counteracts your slight movements when hand holding the camera. Nikon uses the designation of VR for Vibration reduction, Sigma uses OS = Optical stabilization and Tamron uses VC = Vibration compensation.

Other Canon Acronyms

USM = Ultra Sonic Motor which in plain english means the focusing is very quite and fast
II or III = 2nd or 3rd model of a lens. Just like cameras lenses are upgraded, just not at the same rapid rate newer versions generally perform better, have coated lenses and sometimes the addition of IS
UD = Ultra-low Dispersion which means that lens has at least one piece of glass dedicated to controlling chromatic aberration (purple fringing in your images at high contrast intersections, mostly seen at 100%)
STM = Stepper Motor are better at producing smooth, precise incremental movements, such as those required by contrast detect AF, and AF during video. These lenses are often silent during focusing.

Other Nikon Acronyms

AF-S – silent ultrasonic focusing (fast and quite autofocus)
IF – Lens uses internal focusing rather than moving or turning outer elements similar to RF(rear focusing)
ED – Extra-low Dispersion element(s) used in the lens which means that lens has at least one piece of glass dedicated to controlling chromatic aberration (purple fringing in your images at high contrast intersections, mostly seen at 100%)
SIC – Coating used to prevent lens flare

Other Sigma Acronyms

HSM = Hypersonic Motor (fast and quite autofocus)
IF – Lens uses internal focusing rather than moving or turning outer elements similar to RF(rear focusing)
EX – Better build quality
APO = Apochromatic which means that lens has at least one piece of glass dedicated to controlling chromatic aberration (purple fringing in your images at high contrast intersections, mostly seen at 100%)

Other Tamron Acronyms

USD = Hypersonic Motor (fast and quite autofocus)
SP = Super Performance for Discriminating Shooters at least that is what their marketing department says 😉
XR = (Extra Refractive Index) glass which translates into shorter/smaller lenses
LD = Low Dispersion which means that lens has at least one piece of glass dedicated to controlling chromatic aberration (purple fringing in your images at high contrast intersections, mostly seen at 100%)

Next post in the lens series will be about camera brand versus off camera brand (e.g. a Canon lens vs a Sigma lens), Pro lenses, filter sizes and ??? you tell me what else you want to know about lenses.

Canon Users I have a list of recommended lenses

Nikon Users – I am working on one

Take a moment to like this post if you found it useful. And if you have ANY questions find me on twitter, no question is stupid and I am happy to help.

This post and others like it are supported by your Amazon purchases- Canon shooters go buy a nifty fifty right now

Thanks!

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