What Does 35mm Equivalent Mean? How Sensor Size & Lens Focal Length Combine

You can have 35mm film. You can have a 35mm camera. You can have a 35mm focal length lens. That’s a lot of 35mms. And they don’t all refer to the same thing.

What I’m focusing on here is specifically the term “35mm equivalent.” It’s used when talking about lens focal lengths.

The key thing here is that the 35mm refers to the de facto standard that’s used for full-frame digital cameras. And that happens to be based on 35mm film (which actually measures 24mm x 36mm).

Oddly, it’s a reference to film days, but it’s a term that’s only ever used with digital cameras.

That’s because with digital cameras, 35mm is functionally the same as full-frame. It became a de facto standard that a digital camera full-frame sensor is the same size as a frame of 35mm film. So that became the reference point.

When we talk about the “35mm equivalent,” we’re referring to a way to standardize a lens’s field of view, especially when used on cameras with sensors smaller than the full-frame standard. This term becomes particularly useful because not all digital cameras use full-frame sensors; many employ smaller sensors like APS-C or Micro Four Thirds, which significantly affect how a lens captures the world.

In other words, 35mm equivalent means that the lens provides the same field of view on a camera with a smaller sensor as a 35mm lens would on a full-frame or 35mm film camera.

Here’s where the magic of “35mm equivalent” comes into play: it translates the field of view you’d get with a lens on a smaller sensor camera to what you would expect on a full-frame camera. It’s like a universal translator for understanding how wide or narrow your shots will look across different camera systems.

Practical Examples of Crop Factors

For instance, take the beloved “nifty fifty” 50mm lens. On a full-frame camera, it offers a certain perspective—what you see is what you get, a 50mm field of view. However, place that same lens on an APS-C camera (which has a smaller sensor), and the scene captured narrows, mimicking a zoomed-in effect. This is where the “35mm equivalent” comes in handy.

By applying the sensor’s crop factor (let’s say 1.5x for APS-C cameras), we can calculate the equivalent field of view.¹ Thus, a 50mm lens on an APS-C sensor behaves like a 75mm lens on a full-frame camera, in terms of the scene’s framing.

Here’s a practical example. Both of these were taken with the exact same 50mm ƒ/1.4G lens. It’s a prime lens, so there’s no zoom. The first shot is with a full-frame camera, in which case the crop factor is 1, and the 35mm equivalent focal length is 50mm. The second shot with an APS-C cropped-sensor camera with a crop factor of 1.5, so the 35mm equivalent focal length is 75mm. They’re both taken from exactly the same spot; all I did was take the lens off one camera and put it on the other.

Here’s a different approach. These two photos are taken on the same camera with the same lens (and Nikon Z8 and a Nikon Z 105mm ƒ/2.8 Micro). But they’re using a crop mode on the camera. Many full-frame cameras have the option of shooting (and framing) in the native full-frame or using a crop mode. That’s what I’ve used in this case, on a Nikon body using both the FX and DX shooting crops.

Why 35mm Equivalent is Useful

Ultimately, it just comes down to a way of comparing a lens’s reach on different cameras.

It’s confusing, and there’s a lot of room here for a much more logical and consistent term. But it’s nevertheless useful when comparing lenses across different camera systems or visualizing the expected framing without physically testing the lens. And we can put that comparison to use in a number of ways.

It’s particularly useful when comparing lenses and cameras from different manufacturers, as it provides a standard measure.

It’s also useful for mentally visualizing what perspective to expect when using a particular lens on cameras with different sensor sizes.

In practical terms, that’s very handy when choosing which lens to shoot what. On a cropped-sensor camera, for example, you get more telephoto bang for your buck. So if you’re shooting birds, wildlife, or sports, a 200mm lens will get you closer to the action than that same lens would on a full-frame camera. That means you can have a smaller, lighter (and often less eye-wateringly expensive) lens for the same kind of reach. It can also be a useful trick when you need a bit of extra telephoto reach on a full-frame camera to switch to cropped mode, as I did in the second example above.²

It also works well for macro shooting and is one of the reasons that Olympus Micro Four Thirds cameras are so popular for macro shooters.

The converse is true at the wide-angle end such as for landscape, street, or interior photography. You get a wider view on a full-frame sensor. A 20mm lens on a full-frame camera, for example, will give you a much wider perspective than that same lens on an APS-C camera.

1. The 1.5x crop factor for APS-C is approximate. There can be minor variations in sensor size, and some brands use a slightly different size. Most notably, Canon APS-C sensors are a tiny bit smaller, so they have a crop factor of 1.6x. [↩]
2. Switching between full-frame and cropped mode on a full-frame camera doesn’t get you a different end result than just shooting in full-frame and cropped when editing. But it does help with frame the image, because the viewfinder will also adjust accordingly. And it’s also useful when using dedicated cropped-sensor lenses on full-frame cameras (in which case the camera will often make the switch automatically). [↩]