Understanding Crop Factor In Cameras Update 10/2021

crop factors

Even if you’re new to photography, chances are you’ve come across the term “crop factor” while researching or learning the craft. This term appears frequently in product specifications, marketing materials, articles, and books because there are so many different cameras and camera systems available today. You may even hear it in conversations among photographers. If you’re not sure what crop factor means or just want to learn more about it, this article should help you understand it better. As a result, many of the terms and explanations have been simplified for the benefit of newcomers.

1. Background

Due to its widespread use and popularity, 35mm film was the de facto standard before digital. Everyone knew what a 50mm lens on an SLR film camera looked like in terms of field of view and the resulting image, making it simple to understand and discuss different lenses and focal lengths. Digital camera sensor sizes that match the size of 35mm film were impractical due to technological challenges and high manufacturing costs, so camera manufacturers began with smaller sensors in digital SLR cameras. So that people who already invested in a camera system could simply replace their film camera bodies without worrying about repurchasing lenses and accessories, keeping the camera mounts and lenses the same for the transition from film to digital was essential.

A new problem was created when a smaller sensor was used than a 35mm film – both the field of view and the captured images appeared narrower due to the corners of the image frame being “cropped,” or chopped off. Look at the illustration below to see what happens in a camera with a smaller sensor:

crop factors-1.1

Although lenses produce a circular image (often referred to as a “image circle”), the sensor only records a rectangular portion of the scene, meaning that most of the image is wasted. A “full-frame sensor” captures the entire image circle, while a “crop sensor” only captures a portion of the image before discarding or cropping it. It’s important to note that while full-frame sensors are the same physical size as traditional 35mm film (36mm x 24mm), crop sensors are smaller and can vary in size from one system and manufacturer to another. As an example of sensor sizes, here’s one from Wikipedia:

crop factors-1.

Although the terms “full-frame” and “crop sensor” are commonly used to describe digital camera sensors, some manufacturers use a different term for cameras and sensors. When it comes to Nikon cameras, the full-frame ones are referred to as “FX” and the crop-sensor ones as “DX,” while crop-sensor cameras are referred to as “35mm” and “APS-C,” respectively.

For the time being, none of this jargon matters – take another look at the first image and you’ll notice the photos taken on the right side of the camera are the ones you’re looking for. Take note of how drastically different the two images appear. While the full-frame sensor image appears wider, the image captured with the smaller crop sensor appears narrower or more “zoomed in.” Although the focal length and lens may be the same, capturing the same scene with a smaller sensor than full-frame / 35mm film will result in a different, narrower field of view. This is the problem I mentioned earlier.

Using a real photograph as an analogy can help explain how this effect works. Taking an 8×10 photo and cropping it down to a 6×8 with scissors is very similar to using a crop sensor on your camera. However, there’s one thing to keep in mind: depending on your camera’s resolution, the image may appear enlarged. This is nothing to be concerned about for the time being; I will go into more detail about it later.

2. What is Crop Factor ?

When using cameras with different sensor sizes, you’ll notice that your field of view will change and your image will look different. Let’s talk about the crop factor now. What exactly is it, and what does it do for you? Lens manufacturers have devised a simple formula to calculate the “equivalent” focal length of a lens so that photographers can more easily compare the field of view provided by a lens to that of a 35mm or full-frame camera. Due to the cropping and erasing of the image’s corners, a wide-angle lens no longer appears as wide, whereas a telephoto lens brings distant objects closer. The “crop factor” refers to the sensor size as a percentage of the 35mm or full-frame equivalent (see below). The equivalent focal length on 35mm film / full-frame is calculated by multiplying the crop factor number by the lens’s focal length.

Nikon’s “DX” cameras, for example, have a crop factor of 1.5x, so multiplying a 24mm wide-angle lens by this number gives you a 36mm focal length. To put it another way, a 24mm lens on a crop sensor DX camera will have a wider field of view than a 36mm lens on a full-frame camera. You could take the same subject at the same distance with a crop sensor camera equipped with a 24mm lens and a full-frame camera equipped with a 36mm lens and get nearly identical results. Changes in focal length or camera to subject distance can have a drastic effect on perspective, depth of field, and background blur, but that’s another topic we haven’t discussed yet. This does not mean that the images produced would be identical.

Here is a sample list of current cameras that have different crop factors:

+ 1.5x Crop Factor: Nikon DX (Coolpix A, D3300, D5500, D7100); Pentax K-5 II; Sony A5100, A6000; Samsung NX1; Fuji X-A1, X-M1, X-E2, X-T1, X-Pro1

+ 1.6x Crop Factor: Canon Digital Rebel, 70D, 7D Mk II, EOS M2

+ 2.0x Crop Factor / Micro Four Thirds: Olympus OM-D Series; Panasonic DMC Series

+ 2.7x Crop Factor: Nikon CX (J4, S2, AW1, V3); Sony RX100 III, RX 10; Samsung NX Mini

3. How Crop Factor Is Calculated

The math to derive the crop factor is quite simple. Knowing the physical size of the sensor, you first calculate the diagonal using Pythagorean Theorem (a² + b² = c²), then divide the number by the diagonal of the crop sensor. Here is an example on how to derive the crop factor of the Nikon CX sensor:

35mm / Full-frame diagonal: 36² + 24² = 1872, so the diagonal is 43.27 (√1872)
Nikon CX sensor diagonal: 13.20² + 8.80² = 251.68, so the diagonal is 15.86 (√251.68)
Crop Factor: 43.27 / 15.86 = 2.73

So we can see that the crop factor of the Nikon CX sensor is 2.73x, which usually just gets rounded to 2.7x.

4. Common Crop Factors and Equivalent Focal Lengths

Here are the common focal lengths and crop factors, as well as the resulting equivalent focal lengths, to conclude:

35mm 1.5x 1.6x 2.0x 2.7x
14mm 21mm 22.4mm 28mm 37.8mm
18mm 27mm 28.8mm 36mm 48.6mm
24mm 36mm 38.4mm 48mm 64.8mm
35mm 52.5mm 56mm 70mm 94.5mm
50mm 75mm 80mm 100mm 135mm
85mm 127.5mm 136mm 170mm 229.5mm
105mm 157.5mm 168mm 210mm 283.5mm
200mm 300mm 320mm 400mm 540mm

 

This shows that sensor size and crop factor have a significant impact on lens equivalent focal length. The equivalent focal length of a 200mm lens on a small sensor is 540mm thanks to Nikon’s CX cameras’ 2.7x multiplication factor !

5. Equivalent Focal Length

Unfortunately, this is where many photographers become perplexed. Whatever camera sensor you use, the lens’s maximum aperture and maximum focal length will remain constant. When looking at the above table, remember that the smaller sensor does not magically transform your lens into a longer one; rather, it simply crops the image to remove a large portion of it.

crop factors-5

6. Size of Lens and Camera System

Please take a second to notice how much is being shaved off of the first image in this article and the image displayed above. Smaller sensors quickly became popular among manufacturers. It was possible to make smaller, lighter lenses by using less glass because the image circle’s edges were not being used. How come you’re taking up so much room? Initially, this resulted in smaller and lighter lenses, and as technology advanced, new “mirrorless” cameras with crop sensors and smaller lenses were created to be more portable and light weight.

When comparing DSLR lenses, it’s not uncommon to find some that are crop sensor-specific. The smaller image circle of these lenses means that they are incompatible with full-frame cameras. If they are compatible (and have the same lens mount), they will work but will have very dark corners, as shown below:

crop factors-6

Canon EF-S Lens on FX Camera

The addition of abbreviations to lens names was done to make it easier for buyers to distinguish between lenses designed for crop sensors and those not. The following is a list of crop sensor lens abbreviations used by various lens manufacturers:

+ Nikon: DX

+ Canon: EF-S, EF-M

+ Sony / Konica Minolta: DT, E

+ Pentax: DA

+ Samsung: NX

+ Sigma: DC

+ Tamron: Di II

+ Tokina: DX

For example, if you look at a Nikon lens and see “DX” on its label, it indicates that the lens is designed to be used only on crop sensor Nikon DX cameras, while Canon lenses will clearly specify “EF-S” for theirs.

7. Same Mount, Different Lenses

It’s important to remember that some lenses are only compatible with crop sensor cameras, while others, such as those made for full-frame or older 35mm film cameras, will work on both. Even if a manufacturer’s mount is the same, it is not uncommon for their lenses to be sized differently. Nikon’s F mount, for example, is compatible with both full-frame and DX-format lenses. Also, full-frame lenses will work with Sony mirrorless cameras, which have the same Sony E mount but can use either crop sensor lenses or full-frame lenses. Check out this side-by-by-side comparison of the Sony A7 II and Sony A6000 below:

crop factors-7

Both cameras have the same E-mount, but as you can see, the sensors are vastly different in size. While full-frame “FE” lenses are required for the A7 II, you can use both FE / full-frame lenses and regular E series lenses with a smaller image circle when purchasing lenses for the A6500.

Full-frame lenses are generally the best for digital cameras (with a few exceptions), which is why they are more expensive and tend to retain their value better over time than their smaller counterparts. There are only a few professional-level lenses available from either Nikon or Canon, and the rest of the line is mostly made up of long, slow zooms…

8. Sensor Size vs Resolution

As previously mentioned, I had an 810 printed photo. With scissors, you can create a 68 photo, which is exactly what a crop sensor accomplishes. However, we must not overlook the importance of the sensor resolution. Due to the millions of pixels that make up a digital camera sensor, using a smaller sensor should result in fewer pixels, correct? No, not at all. Two sensors with the same resolution could have physically smaller pixels if the sensor is made (in some cases, a crop sensor could actually have more pixels than a full-frame sensor).

Nikon’s D4 has a 36.0 x 23.9mm full-frame sensor with 16 million pixels, while the D7000 has a 23.6 x 15.6mm sensor with the same number of pixels. While both cameras have the same number of pixels, they differ in terms of pixel size because the sensors are so different in size. When comparing the two cameras, the D4s’ pixels measure 7.3m, while the D7000’s are 4.78m, meaning the D4s’ pixels are closer together. In low-light situations, the Nikon D7000’s image quality simply cannot compete with the Nikon D4’s due to the D7000’s smaller pixels producing more noise and a reduced dynamic range. So, instead of talking about sensor sizes, manufacturers prefer to use the term “megapixels.” Instead of emphasizing the small sensor, they want you to focus on the flashy megapixel count. No matter how high the resolution of your phone camera is, that doesn’t mean you’ll get the same quality images as you would with a DSLR.

Modern crop sensors, on the other hand, have improved dramatically in their ability to handle noise, especially at low to medium ISO settings. You won’t be able to tell the difference between full-frame and 1.5-1.6x crop sensors when shooting in good lighting. Crop sensor cameras, then, have a distinct advantage in this situation. If two cameras with different sensor sizes but the same resolution perform similarly in daylight, the camera with the smaller sensor may actually be advantageous for getting closer to the action. Image cropping and magnification are both happening at the same time. Going back to our 8×10 printed photo example, consider cutting the corners off to make a 6×8, but then scanning and printing the new image to make it an 8×10 size. That’s essentially what’s happening here.

Long lenses used on crop sensor cameras give sports and wildlife photographers more “reach,” so they may prefer this setup. A 300mm lens on a crop sensor camera, for example, has the same field of view as a 450mm lens on a 35mm / full-frame camera. There is a significant increase in reach if low-light performance is not an issue. Naturally, this assumes the lens is capable of resolving that much detail in the first place. Because they weren’t built for high-resolution sensors, some older lenses may be unable to resolve enough detail to give you a greater field of view….

This article should have made Crop Factor a little more understandable. But don’t let the technicalities get in your way – learn to make the most of your current equipment and put your energy into creating better images. Remember that most modern cameras are fantastic, so the only thing standing in your way of taking photos of professional quality is yourself…