Canon 100mm EF macro lens

My Canon Macro Lens EF 100mm 1:2.8 USM

See that lens description in the headline above? That’s what it says (minus the “My”) on my Canon macro lens. If you’re not yet familiar with macro lenses, much of that may not mean anything to you. So, I’m going to break it down piece by piece and explain what each of those words and abbreviations means.


Okay, this one you knew already. It’s simply the brand of the device. It’s still kinda important to note though, because it matches the camera body that I own. Of course, there are other brands that will fit onto my Canon camera too, but Canon attached to Canon does have a nice feel.

Canon 100mm EF macro lens

Macro Lens

These two words really need to be kept together because that’s what this piece of equipment is – a macro lens. It’s not obvious just from glancing at it – unless you’re a real expert with these things – that this is a macro lens. Sure, it’s longer than many, but there are other types of lenses that are not macros and yet are longer than “normal” too.

You can argue with some folks all day about what is and what isn’t a true macro lens. I’m not going to get into that, and I know a lot of other macro photographers don’t bother either. Let’s just agree for now that a macro lens can make really tiny objects look really big.

Nuf said.


This may be the first item in the lens description that puzzled you. “EF” stands for “electro-focus”. This simply means that there’s a tiny motor inside the lens that is dedicated to handling the focusing task for you automatically. This assumes that you have the autofocus (AF) switch actually set to AF. I don’t. I have mine set to MF, which means Manual Focus.

Canon macro autofocus vs manual focus

Why do I insist on doing the focus work myself? Well, when taking macro photos, the target can go in and out of focus with my slightest movement. Or, if I’m shooting flowers outside and there’s the least bit of breeze, the target itself starts to move. This can quickly and easily confuse the autofocus mechanism making the lens jerk in and out (as it’s supposed to) over and over again never giving me a good time to snap the picture.

There is a time when autofocus for macros makes sense. If I’m using a tripod and shooting an object that can’t move on its own, I’d flip the toggle switch to AF and let the lens do its thing. Most of the time, I don’t have that option, so I leave it set at MF.


100 millimeters is the physical length of the lens from front to back. What’s good about a longer lens normally only matters if you’re photographing live subjects like insects. Being alive, the insects are aware of you (generally speaking). The closer you get, the more jittery they become. The longer your lens, the farther away you can stay and still get a great macro shot.

With this 100mm macro lens, I can stay about 6 inches away from my subject and still get one-to-one (aka 1:1) results. I won’t go into the nitty-gritty of 1:1 here. Suffice it to say that I can get a big picture by staying 6 inches away.


This 1:2.8 figure looks similar to the 1:1 just above, but it doesn’t refer to the same thing. Sometimes you’ll see this written as f/2.8. It refers to the “highest” f-stop that you can set the lens to. Again, I won’t get into all the details here, but when I say “highest”, I mean the widest diameter I can set the aperture (opening) of my lens to.

Okay, I’ll get into the math just a little. Notice that the f/2.8 looks like a fraction, where “f” (focal length) is the numerator and 2.8 is the denominator. Hopefully you know that the smaller the denominator, the larger the number. For example, 1/2 is larger than 1/16. Keeping that in mind, it makes sense that a setting of f/2.8 gives you a larger lens opening than f/32.

A larger opening obviously lets in more light, which is usually a good thing. What’s not immediately obvious is that a larger opening also gives me a shorter focal distance, or depth of field. This is what’s so important to macro photographers. Many times I want to open that lens wide to let in a lot of light, but then I can only get a good focus on an extremely thin slice of my subject (from front to back, near to far) making a good chunk of the flower or bug or whatever look out of focus.

I could “stop down” to something like f/32 to get the whole thing in focus, but then I get almost no light entering my lens. I can adjust the ISO setting to compensate, but then it starts to look all grainy. So I go back to my aperture setting and open it up a little more…and ‘round and ‘round we go.

Nuf said on that for now too.


The USM abbreviation stands for Ultrasonic Motor. (Don’t ask me why it’s not just UM. Ask Canon.) This is a mechanism that speeds up the autofocus motor. As such, it doesn’t really matter to me, since I have AF turned off anyway.

Not IS

You may see a lens very similar to mine that also includes “IS” in its description. Such a lens adds “image stabilizing” into the mix. (It also adds to the price of the lens.) Much like AF, this isn’t something I’m very interested in either. As the name suggests, this feature is supposed to help keep the image “still” when my hands move so I can get a focused shot. Most of the time, I can either keep still enough or use other methods to achieve similar, if not better, results.

There are situations where having an IS lens is good, even necessary. It’s just that I don’t find myself in those situations very often.

Other Features of My Macro Lens

There are really just two other things I should mention about my lens. I haven’t discussed them to this point because I almost never use them or even look at them.

The first is the focusing distance range selector switch. I can set this either to 0.31m (to infinity) or 0.48m (to infinity).

I always set it to 0.31 meters. Why would I want to set it to a longer minimum distance? To make my autofocus work faster. But since I don’t use autofocus, it doesn’t make sense to use 0.48 meters.

Canon macro lens distance scale

The other feature is the distance scale. I can see measurements in feet or meters, as well as a one-to-x setting. I never look at this. I think the only reason to do so would be for getting the exact same results with the same target on different occasions. When shooting macros, especially wildlife, this is virtually never going to happen.

Not that it matters, but you may have noticed in the pictures above that this is a red dot lens. My other Canon lens – a zoom EF-S 18-55mm 1:3.5-5.6 IS – is a white square. Go figure.