Different lenses will have different numbers on them, but regardless of which numbers are on a lens, they can still be pretty confusing if you’re not sure what they all mean. Fortunately, it’s not too difficult to figure out! Let’s take a few minutes to look at those numbers and decipher their meaning.
We’ll use the Nikon 18-55mm kit lens as an example for this post, but once we break down the numbers on the lens and examine what they mean, it’ll be pretty easy for you translate those curious numbers on whichever lens you happen to shoot with.
Focal Length: 18-55mm
Looking at the image above, find the sequence of numbers that are just under the Nikon DX logo. See where it says, AF-S NIKKOR 18-55mm 1:3.5-5.6G? The 18-55mm is the focal length of the lens. In this case, we’re looking at a zoom lens which has a range of focal lengths that are 18mm at the widest, but can zoomed all the way to 55mm. If you have a prime lens (one that doesn’t zoom), you’ll most likely only see one number there meaning your focal length is fixed to that length. For example, 50mm, 105mm, etc.)
You’ve probably already put together that the “mm” stands for millimeter, but if you’re curious about what that’s actually measuring it’s measuring the distance between your camera’s sensor and the point of convergence of the lens. When zoomed all the way out to 18mm, the point of convergence of the lens above will be 18 millimeters away from the camera’s sensor. As you zoom out, the point of convergence moves farther from the sensor (and that increased distance is what creates the zoom effect).
Another point of interest while we’re talking about focal length, is that if you use a lens intended for use on full frame cameras on a crop sensor/APS-C camera, the focal length of the lens will increase by approx. 1.5 times (depending on the camera you are using).
Maximum Aperture: 1:3.5-5.6
The set of numbers that follow the focal length reveal the maximum possible aperture (or f number) for that lens. The 1: that appears before the 3.5 is there because we measure f stops in ratios, you can typically disregard the 1: altogether. The next numbers we see are 3.5-5.6. That is the range of maximum apertures the lens is capable of depending on what focal length you are shooting at. In this case, if you are shooting with the Nikon 18-55 at the widest possible focal length of 18mm, the maximum (widest) aperture you can open the lens up to is f3.5. As you zoom the lens to longer focal lengths, the maximum aperture will decrease. The 5.6 on this lens tells us that at it’s longest focal length of 55mm, the widest you will be able to open your aperture to is f5.6.
Remember, the smaller the f number, the larger the aperture is. The larger the aperture, the more light it lets through. F 3.5 is a larger opening than f5.6, thus f3.5 lets more light into the camera, which makes it a “faster” lens. Lenses with small apertures are generally more desirable for this reason and some lenses will have apertures as wide as f.1,2 or even f .8!
Minimum Focusing Distance: ∞0.28m/0.92ft
Looking at the photo just above, find the series of numbers that are on the bottom left of the front of the lens–the sequence that begins with the infinity symbol (∞). The numbers next to the infinity symbol are the minimum focusing distance of the lens. in other words, this specific lens is capable of focusing on an object that is anywhere from 0.28 meters (or 0.92 feet) away from the camera to infinity.
Filter Size: Ø52
If you see an “Ø” character followed by a number, that number measures the diameter of the lens itself. Mores specifically, it measures the very end of the lens, which is useful to know because this number will also be the size of any lens caps or screw on filters that will the lens. For the Nikon 18-55mm DX, the lens cap size is 52.
Now, What Do Those Letters Mean?!
You’ve probably also noticed a bunch of seemingly random letters grouped in with all those numbers. Depending on which lens you have you’re likely to see letters like VR, IS, USM, and lots of other possible combinations. Of course, all these letters have specific meanings, but this is where things start getting a little tricky to explain. Each brand of lens (Nikon, Canon, Sigma, Tamron, etc…) will all have their own set of abbreviations, as will different models. The abbreviations stand for a variety of things ranging from whether or not they have image stabilization, whether they were designed for use with full frame or crop sensors, the type of glass used, etc.
The best way to find out what the abbreviations on your lens mean is to look them up the manufacturers website or consult the manual that came with the lens. Since most people will only have one or two different brands of lenses, the abbreviations are fairly simple to memorize.