What Does the mm Mean on a Camera Lens?

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We’re a little biased, but we think photography is one of the best hobbies in the world. With just a little practice, you can quickly start capturing the world around you in all its glory. Nothing helps you appreciate your surroundings more than a good photo shoot.

One thing that we don’t love about this hobby, however, is how intimidating it can seem to newbies. For example – what does the ‘mm’ mean on a camera lens? Why are there so many different measurements floating around?

If you’re wondering how to read camera lens specs then you’ve come to the right place. On this page, we’ll run through what the mm measurements on lenses are actually referring to. We’ll explore some of the most common examples and bring you up to speed on the basics.

Read on to up your photography game.

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What Does Lens Size Mean – Focal Length

So what kind of measurement is ‘mm’ referring to anyway? The first thing to explain is that this is a measurement in millimeters. Older lenses and formats could sometimes use measurements in cm or even inches, but this is increasingly rare. Millimeters has been the industry standard for many years now.

So what are we actually measuring in millimeters? The answer is focal length. These numbers tell you about the effective focal length of any lens you’re considering. While there’s a whole lot of optical science involved with focal length, it’s not too difficult to get to grips with the basics.

The focal length of a lens tells you how well it will perform in certain situations. It explains the following:

  • How much you’ll be able to fit into frame
  • How far away you’ll have to be from your subject(s)
  • How big objects will appear in the shot (magnification)
  • How much ‘wiggle room’ you’ll have to keep things in focus

Higher focal lengths (eg 300mm) offer a narrower field of view and higher levels of magnification (things appear bigger in the frame). The same is true in reverse – smaller focal lengths deliver wider viewing angles with lower magnification.

You’ll be buying lenses with different ‘mm’ numbers depending on the type of photography you want to do. A macro lens will have a very different focal length to a telephoto lens, for example.

What do the Numbers on a Camera Lens Mean – Prime Lenses Explained

So why do some lenses have just one ‘mm’ number (eg – 35mm) while others offer a range (eg – 75mm-300mm). The answer is that some lenses can zoom and some are fixed at one focal length. When a lens is fixed to one focusing distance, it’s called a prime lens.

As a general rule, these lenses can offer higher levels of optical performance and sharpness vs a zooming lens. What they lack, however, is the versatility that many people need when working.

You won’t be able to zoom in to your subject at all. You’ll have to physically move closer or further away if you want to tweak your shot.

A zoom lens is different in that it offers users a range within which a photo can be successfully focused. A 75mm-300mm lens, for example, can keep subjects in focus anywhere within this range.

What Does ‘35mm Lens’ Mean?

35mm is one of the most common focal lengths for camera lenses. The format is very well suited to street photography and can make for a great all-rounder travel lens. It’s worth keeping the following in mind about 35mm lenses:

  • They offer wide viewing angles (good for group photos)
  • They must be kept fairly close to their subject(s)
  • Can be great for macro/ close-up shots
  • Can’t zoom

What Does ‘50mm Lens’ Mean?

Another super common focal length you’ll see for modern lenses is 50mm. These products are often referred to affectionately as ‘nifty fifties’ thanks to their versatility. A 50mm lens is a little narrower than a 35mm option but offers significantly more wiggle room when setting up your shot.

If you’re set on buying a prime lens, we strongly recommend considering a 50mm product. They’re super versatile and tend to offer excellent levels of optical performance. The ubiquity of this focal length also means that there’s tons of choice out there when it comes to the specific lens you choose.

How to Read Camera Lens Specs

For better or worse, focal length isn’t the only thing you’ll have to think about when looking at lenses. This section is designed to introduce you to some other common terms, settings and confusing letters that could trip you up if you’re not familiar with them.

The main thing to keep in mind is that none of this is rocket science. Anyone can get into photography – don’t let the snobs online put you off. All you need to do is read up on some of the basics.

Aperture Ratios

When looking at different lenses online, you might have noticed terms like this: “1:2.8” or “f/2.8.” So what on earth is this referring to? The answer is aperture. The terms we just introduced are describing the maximum aperture of a lens.

In other words, it tells us how wide the opening of a lens is capable of going. When looking at zoom lenses, you’ll probably see an aperture range. In much the same way that the focal length of a zoom lens is represented by a range, the same is true of that lens’s aperture.

For example, the following – “f/2.8-5.6” or “1:2.8-5.6” tells us that a lens offers a max aperture range between f/2.8 and f/5.6. Your aperture setting determines how much light can enter your lens when shooting.

Understanding the aperture offered by a given lens will go a long way in helping you take better photos.

What Does ‘Ø’ Mean?

While this symbol can seem super intimidating to the uninitiated, it’s just referring to the diameter of a lens. A Ø77mm lens, for example, will have a front screw mount 77mm in diameter. This tells you which cameras and other accessories it’s likely to be compatible with.

What Does AF/MF Mean?

Have you been working with your lens and noticed a switch labelled “AF/MF”? Don’t worry – this one’s super simple. This switch allows users to toggle between the autofocus and manual focus modes on your camera.

It’s found most often on Nikon and Canon DSLRs but is fairly ubiquitous. Once you’re ready to take your photography to the next level, try switching to manual mode for your focus to get the sharpness just right.

What Do “IS” and “VR” Mean?

These stand for image stabilization and vibration reduction respectively. Most modern lenses come with technologies built in that are designed to reduce the results of camera shake and keep images free from noise.

Look for “IS,” “VR,” “Image Stabilization” or “Vibration Reduction” near the glass of your lens to make sure you’ll have this feature at your disposal.

What Does “Mark II/III” Mean?

You see this one a lot with lenses, especially with products from Canon’s EOS line. This is referring to the version of a specific lens. “Mark II” is more recent than the original, and so on.

Conclusion

We hope this page has cleared up any confusion. The world of photography can be a confusing place for the uninitiated. The thing to keep in mind, however, is that you don’t have to be an expert to take gorgeous photos.

Check out the other guides and explanations on this site to continue growing as a photographer.

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