If you use any kind of digital camera with interchangeable lenses, you’ve probably heard the term crop factor at some point. But what does that mean? And how is it relevant to you?
First off, if you only plan to use lenses that were made for the type of camera you have, crop factor probably isn’t particularly relevant to you. But sometimes a particular lens mount has some gaps in it, and camera owners will use lenses from other systems with adapters. You may have already guessed that you can’t just simply use a Canon lens on a Nikon body, but even within the same manufacturers, there are often differences that it’s important to be aware of.
Crop factor is a function of sensor size. Here is a breakdown of a few of the most common sensor sizes and how crop factor affects them.
It might seem a little odd that I start with a sensor that has no crop factor. But it’s important to know about full-frame because it’s considered a baseline sensor size for comparison purposes. The sensor in a full-frame digital camera is 36mm x 24mm, which is also the size of a frame of 35mm film. For this reason you’ll sometimes see lens focal lengths described in terms of their “35mm equivalent.” I’ll explain more about what that means when I describe some of those sensor sizes.
The beauty of this is that if you have a Canon or Nikon autofocus film camera, you can use a lot of the same lenses on the full-frame digital cameras by those manufacturers. However, if you want to be sure about the compatibility of particular lenses and bodies, be sure to look up that information. Often the manufacturer’s website will have it.
Usually when you hear talk of a “crop sensor” DSLR, this is the size being discussed. Most entry-level DSLRs have a sensor of this size. As you can see with the image at the top of this post, there are slight differences between manufacturers, but they are not very significant.
APS-C cameras typically have a crop factor of 1.5 or 1.6. This means that a lens made for these cameras is sort of the equivalent of a full-frame lens 1.5 or 1.6 times its size.
For example, many APS-C cameras come with a kit lens that is 18-55mm. This lens covers about the same range as a 27-82.5mm lens (if one existed) would on a 35mm camera. However, don’t try to mount this lens on a full-frame camera and expect to get those kinds of results. Even if the lens will mount, it won’t cover the larger sensor. That said, many full-frame cameras offer an APS-C shooting mode that you can use in a pinch if needed.
So what about the other way around? Since the full-frame sensor is larger, as long as the lens and the camera have the same mount, covering the sensor shouldn’t be a problem, right? Right.
The only thing you have to worry about when mounting a full-frame lens on an APS-C camera is that the lens won’t behave quite the same way. For example, if I take a full-frame 50mm lens and mount it on my APS-C camera, I have to multiply that focal length by the crop factor of my camera, which is 1.5 in this case.
50mm full-frame lens
* 1.5 APS-C crop factor
= 75mm effective focal length
Therefore, that 50mm full-frame lens will behave like a 75mm lens while attached to an APS-C camera.
By the way, if you’re thinking that seems like a great trick for portraits, you’re right. My sister does this with her kids all the time.
Micro Four Thirds
Micro Four Thirds (also known as MFT), is a lens mount for a certain type of mirrorless camera, generally made by Panasonic or Olympus. Any MFT lens will work on any MFT camera, although, as you might expect, each manufacturer does include features that are designed to play well with their own cameras. MFT sensors have a crop factor of 2.
Nikon 1 series
These cameras have a 1″ sensor and a crop factor of 2.7. You can use an adapter to mount APS-C or even full-frame lenses to these cameras, but there’s a good chance you’ll throw off the weight balance doing so, since Nikon 1 cameras are designed to be small and extremely portable. This can be a factor with APS-C cameras as well, but usually not to the same degree.
I hope this cleared up any confusion you might have had about crop factors with lenses. Now you can confidently move between sensor sizes while understanding what the differences are!
Note: this post is slightly edited from the original published version.