When you buy a new camera, you have a variety of options regarding the sensor size.
Some cameras - typically the more expensive varieties - have what's called a full frame sensor.
Other cameras - usually the consumer-grade types that a lot of beginner photographers purchase - have what's called a crop sensor, which is smaller than a full frame sensor.
As if that's not confusing enough, there are different types of crop sensor cameras, including today's popular APS-C and micro four-thirds formats.
But what the heck does all that mean? And why is it important?
Let's clear things up...
Full Frame vs. Crop Sensor
A full frame sensor is one that's roughly equivalent to the size of a 35mm piece of film. That makes the sensor about 24mm x 36mm in size.
The larger sensor size comes with a few benefits, including higher resolution images, larger pixels for better sharpness, and better low-light performance.
Of course, the larger the sensor, the larger the camera body that's required to house it, so full frame cameras - like the Canon EOS 5D Mark IV shown above - tend to be larger and heavier than their crop sensor counterparts.
And as I alluded to in the introduction, full frame sensors tend to be in more expensive cameras, so budgetary concerns are more of an issue with a full frame camera.
On the other hand, crop sensor cameras are essentially the opposite. They're smaller, more compact, and lighter in weight because of the smaller sensor size.
Additionally, because of the smaller sensor size, the cameras tend to be less expensive, though there are some mid-range models that can be quite pricey.
The smaller sensor means smaller pixels that produce images that aren't the same quality resolution or sharpness. Low-light performance is usually not as good as a full frame camera, either.
That isn't to say that crop sensor cameras are bad - quite the contrary. There are many excellent crop sensor models available, including the Nikon D7200 shown above.
But in a head-to-head matchup of image quality and camera performance, full frame models tend to outperform crop sensor models.
The other thing to know about crop sensor cameras is that the size of the sensor varies from one manufacturer to the next.
For example, a Canon EOS Rebel T6i has a sensor that's 22.3mm x 14.9mm. Conversely, the Nikon D5300's sensor is 23.5xmm x 15.6mm.
Not only can the varying sizes of sensors in crop sensor cameras be on the confusing side, but the size of the sensor also means that different cameras have different focal length multipliers (sometimes called crop factors) as well (more on that below).
Get a few more insights on full frame and crop sensor cameras in the video above from Karl Taylor.
Learn More:
- What You Need to Know About Full Frame vs. Crop Sensor Cameras
- Weighing Your Options: Is a Full Frame Camera Right For You?
Focal Length Multiplier in a Nutshell
As noted above, a lot of cameras today have a cropped sensor, most typically either of the APS-C or micro four-thirds varieties.
This means that their sensors are smaller than the "normal" full frame 35mm equivalent sensor.
That's important because the focal length of a lens is based on that full frame 35mm format. In other words, a 50mm lens behaves like a 50mm lens on a full frame camera and is considered a "normal" or "standard" lens at that focal length.
Similarly, a 24mm lens on a full frame camera behaves like a 24mm lens and represents a common focal length for wide-angle lenses.
Where the focal length multiplier comes into play is in determining the effective focal length of a lens on a crop sensor camera.
The focal length multiplier is a simple formula that takes the size of the camera's sensor into account to determine how the lens will behave on a crop sensor camera.
It's important to understand the focal length multiplier because it can drastically change the effective focal length of a lens that you use.
For example, where a 50mm lens acts like a 50mm lens on a full frame camera, on a crop sensor camera it might behave like an 80mm lens.
That's a huge difference in the way the lens behaves - instead of a standard or normal field of view, you get a short telephoto field of view that has a zoomed in effect.
In other words, if you photograph a landscape with a 50mm lens and a full frame camera, and a friend photographs the same landscape from the exact same spot with the same 50mm lens on a crop sensor camera, your image will have a wider field of view than your friend's. That's all due to the focal length multiplier of the crop sensor camera.
Watch the video above from FocusED to get an overview of crop factor.
Learn More:
- Focal Length and Field of View Explained in 4 Steps
- Camera Lens Terms Explained for Beginner Photographers
Calculating the Focal Length Multiplier
So, the focal length multiplier tells us the effective focal length of a lens on a crop sensor body.
But the focal length multiplier on crop sensor cameras varies from one manufacturer to the next.
For example, Nikon crop sensor cameras have a crop factor of 1.5x, as do Fuji crop sensor cameras. Canon crop sensor cameras have a crop factor of 1.6x, while Olympus crop sensor cameras have a crop factor of 2x.
As a result, you need to multiply the crop factor of your specific camera model by the focal length of the lens to get the effective focal length.
For example, if you're shooting with a Canon crop sensor camera and a 50mm lens, that lens would have an effective focal length of 80mm because of Canon's 1.6x crop factor (50mm x 1.6 = 80mm).
A 50mm lens on an Olympus crop sensor camera would have an effective focal length of 100mm because of Olympus' 2x crop factor (50mm x 22 = 100mm).
It's a simple formula and one that can save you a lot of headaches when purchasing lenses, because looking at the identical images above, you can see how much wider field of view you get with a lens on a full frame camera (the first image) than you do with a crop sensor camera (the second image).
By that I mean that if you want a wide-angle lens for landscape photography with your crop sensor camera, you won't get wide-angle performance from a 24mm lens.
Instead, you'll need an even wider focal length - say 12mm - to get that wide-angle look on a crop sensor camera.
Learn More:
Wrapping It Up
When you're just starting out in photography, all the terms like full frame, crop sensor, focal length multiplier, and so on, can be extremely confusing.
Hopefully, this guide has cleared some of that confusion up for you.
In the end, it's really just about figuring out the crop factor of your specific camera, multiplying it by the focal length of the lens, and getting an effective focal length.
Understanding how a lens will behave on your crop sensor camera will enable you to make a more informed decision when buying a lens and will allow you to get the type of lens you need to take the type of photos you want.
With that, I encourage you to do a little research on your camera model to determine the crop factor, practice getting the effective focal length of various types of lenses, and use that information to get the best lens for the type of work you want to do.