What Do the Numbers on Camera Lens Mean?

The numbers on a camera lens indicate the focal length, aperture, and thread diameter. These numbers can play a significant role in figuring out what a lens’s best use is and its weaknesses.

My name is Caleb, and I have more than five years of experience as a photographer. I’ve mainly specialized in sports photography and shot games across various sports, from the college to the semi-pro level.

In this article, I’ll explain what the numbers on camera lenses mean and what you should look for when buying a lens yourself. If you’re shopping for a lens, and the numbers confuse you, keep reading for a simple explanation.

What do the Numbers on a Camera Lens Mean?

In simple terms, the numbers on a camera lens represent the focal length in millimeters and the max aperture. The focal length tells you how much “zoom” the lens has, while the aperture number, or f-stop, informs you of the maximum aperture.

A smaller number for focal length makes objects appear further away, and you can fit more into the frame. On the other hand, a larger number makes objects appear closer and provides a narrower frame.

You can consider 50mm a baseline of sorts. 50mm lenses offer a view that’s pretty close to the human eye, with lenses above or below that number giving narrower or wider frames, respectively.

Understanding the aperture number is just as simple. The lower the number, the wider the maximum aperture. It’s usually written on the front of the lens near the focal range in a format like 1:2.8 or f/2.8. In this case, the ‘2.8’ is the part we need to pay attention to.

Why Does Max Aperture Matter?

The widest aperture is written on the lens because it’s a pretty important spec. To understand why, you need to know what aperture means in the first place. 

It’s the measurement of how wide the lens opens when you press the shutter button. A wider aperture allows more light into the lens, producing a brighter photo. This is why having a wide maximum aperture is crucial for good night photography.

A wide maximum aperture also ‘freezes’ the subject more. For action or sports photographers, this is essential to getting sharp, non-blurry shots of moving subjects.

F/2.8 is considered a good enough max aperture for professional photographers and those in demanding niches like sports, although many prime lenses can go wider than f/2.8.

Fixed vs. Variable Aperture

You might have noticed that some lenses only list a single number for their maximum aperture, while others list a range. That’s because the aperture can be fixed or variable, depending on the lens.

Lenses with a fixed aperture have a consistent max aperture no matter how zoomed in the lens is. With variable aperture lenses, on the other hand, the maximum aperture decreases when the lens is more zoomed in.

As an example, a lens could have a max aperture of f/3.5-5.6. In that case, the f/3.5 would only apply toward the closer parts of the focal range, while the f/5.6 would apply further out.

Variable aperture lenses are cheaper than their fixed aperture counterparts but have the obvious drawback of worse performance when zoomed in.

Prime Lenses and Zoom Lenses

Just like the aperture can be fixed or variable, so can the focal length. Lenses with a fixed focal length are called prime lenses, while lenses with a variable focal length are zoom lenses.

Prime lenses have a fixed focal distance. For example, you may decide to use a prime lens of 35mm. A lens like this will only shoot with a 35mm focal length.

Zoom lenses have a variable focal range. For example, one common range for zoom lenses is 24-70mm. With a lens like this, you can adjust the focal length freely between those numbers.

Prime Lenses vs. Zoom Lenses: Which One Is Better?

While zoom lenses are the more common option because of their convenience, both types are still usable for many different kinds of photography.

Obviously, zoom lenses carry the advantage of versatility. A single zoom lens may replace three or four prime lenses in your camera bag. You’ll also need a zoom lens if you’re shooting moving subjects.

Prime lenses, on the other hand, sometimes have better image quality. They often have a wider maximum aperture, making them better at low-light shooting than zoom lenses. 

Another advantage on their side is price. Prime lenses trend cheaper, sometimes by a significant margin. The question of which lens type is better largely depends on what kind of photography you’re aiming for and how much you value versatility.

Thread Diameter

You may have noticed another number that we haven’t covered yet. The number is written in millimeters and is usually next to an ‘O’ with a slash running through it. This represents thread diameter.

Thread diameter tells you the circumference of the lens, which you can use to ensure you get the right size lens filter. 

Lenses come in various sizes, and filters aren’t one-size-fits-all, so before buying one, you should check this number and ensure it matches up with the filter you’re considering.

What Are Different Focal Lengths Good For?

Now that you know about wide and narrow lenses, you’re probably wondering when to use either one. Luckily, it’s not that complicated. Wide lenses are best for fitting more into the frame, while narrower lenses are better for shooting from a distance.

For example, if you’re trying to take a shot of an expansive landscape, a 24mm wide lens would allow you to fit more of it within the frame.

In contrast, if you wanted to focus in on a specific subject standing in the distance, a narrower 70-200mm lens would be a better choice. A lens like this makes objects appear closer, letting you take a close-up shot while standing back.

Ultimately, there’s no right or wrong here. Lenses of all focal lengths have their uses, and many photographers carry both wide and narrow lenses in their bag to be prepared for any situation.


Here are some of the frequently asked questions about focal length and aperture.

Is it Better to Have a Higher or Lower Aperture?

In many cases, it’s better to have a lower f-stop number. A lower number means that, when shooting at maximum aperture, you can let more light into the lens. This makes for better low-light performance and helps with sharpness and clarity.

What Does 75-300mm Mean?

75-300mm on a lens would indicate a zoom lens with a variable focal range of 75-300mm. Lenses like this are highly versatile but usually sacrifice a decent amount of performance to achieve that flexibility.

Are Aperture and Focus the Same Thing?

No, they are different concepts. The aperture measures how much the lens blades open to allow in light, while the focus measures how zoomed in the lens is.


The numbers on a camera lens usually indicate the focal range, maximum aperture, and thread diameter. Each number plays its own role in determining how the lens performs, and you can tell a lot about a lens by understanding these numbers.

What kind of lens fits your own photography goals? Let us know in the comments.

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