If you’ve ever looked at a camera lens, you’ll have noticed that they have a series of numbers and letters inscribed on them. This is like the lens’ business card, containing all the important technical data about it. By including these numbers and letters, your lens is letting you know what it’s capable of and how to get the best out of it.

Thumbnail 3 4 Things You Need to Know to Work with Your Lens

Although each brand uses its own nomenclature, you’ll usually find 4 basic specifications on all lenses: millimeters, aperture, motor, and diameter. Let’s take a look at each one and find out where to locate them.

Table of Contents

  1. Millimeters
  2. Aperture
  3. HSM – USM – STM
  4. Diameter
  5. Summary and guide


This specification is easy to identify. You’ll see a number followed by “mm”, as in this example:

DSC00010 4 Things You Need to Know to Work with Your Lens

The millimeters of the lens refer to the focal length that you can attain in your images. In other words, this is the depth of field that you can capture in your photo or video. Hold on, do you need help deciphering this information? To get the best out of your lens and to know which situations require certain settings, first remember that fewer millimeters means a longer focal length, and vice versa.

What does that mean in practice? Let’s go over a couple of examples:

To put it simply, a lens with a longer focal length captures a wider scene than a lens with a shorter focal length. With a longer focal length you’ll be standing further away than when you’re shooting with a shorter focal length.

And since we are talking about moving towards and away from the subject, it’s also important that you know that millimeters are different for prime and zoom lenses.

What is the difference? On a fixed lens, the millimeters are fixed at that specification. It’s as simple as that. 🙂

On a zoom lens, you have a range of millimeters and focal length, indicated by two numbers separated by a dash, as you can see in the example above.


This specification can be found as a proportion on the lens, you will see “1.” followed by other numbers, like this:

DSC00009 Aputure 4 Things You Need to Know to Work with Your Lens

What do these numbers mean? The figure that follows the “1.” indicates the maximum aperture that the lens’ diaphragm allows. As in other aspects of photography (and life), less is more: The smaller the number, the larger the possible aperture of the diaphragm. Check out these examples:

Canon 50 mm comparacion 4 Things You Need to Know to Work with Your Lens

All are 50mm lenses, but differ in their aperture: 1.2, 1.4, and 1.8. All three have fixed millimeters and the aperture varies depending on what you set on your camera, going up to the maximum figure indicated (1.2, 1.4, and 1.8).

In the case of these fixed lenses, the aperture is also fixed. On some zoom lenses, however, the aperture can be variable and, like millimeters, you’ll see it represented as a range, like this:

image 4 Things You Need to Know to Work with Your Lens

On kit lenses, or default lenses of some cameras, the aperture may vary depending on the zoom you use. The more you zoom, the smaller the aperture the lens will allow, meaning less light will enter.

Both larger aperture prime lenses and fixed aperture zoom lenses are much more expensive.


No, the cat didn’t just run across the keyboard! These acronyms show the different types of motor that the lens has. Yes, that’s right – lenses have motors. 😉

DSC00010 STM 4 Things You Need to Know to Work with Your Lens

First of all, here’s what the acronyms stand for:

  • HSM: Hypersonic motor
  • USM: Ultrasonic motor
  • STM: Stepper motor

What does all that mean in practice? In short, HSM and USM motors are intended for professional photography jobs, while STM motors are ideal for hobbyists and video, as they make less noise when you use automatic zoom.


This specification, which is represented by the diameter symbol (Ø), is also measured in millimeters:

DSC00008 4 Things You Need to Know to Work with Your Lens

This measurement is important when you’re buying filters and other accessories since each lens has a different diameter. Even if you have two 50mm lenses, their diameters can vary.

Summary and guide

While some lenses may include more information beyond this data, these are the 4 basic specifications for identifying different lenses. By keeping this information in mind, you’ll have a better idea of how to get the most out of your lenses.

Remember that:

  • The diameter refers to the focal length that the lens allows you. The smaller the number, the greater the possible focal length, and vice versa.
  • Aperture can make all the difference in the price of the lens. A larger aperture or a fixed aperture in zoom lenses means a more expensive lens.
  • If you’re just starting out in photography, an STM motor is more than enough. 😉
  • Before buying filters or accessories, make sure the diameters match!

And so you don’t forget anything, I recommend keeping this guide in your camera bag for easy reference:


Hanns Schmelzer

¡Hola! Soy Hanns. Nací y crecí en Venezuela, pero vivo en Berlín desde 2014. Puedo hablo tres idiomas (alemán / inglés / español), disfruto cocinar y soy un apasionado por los videojuegos. Pero sobre todo, ¡me encanta todo lo que tenga que ver con las imágenes en movimiento!

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