Understanding Crop Factor

7 March 2019 2:34:54 PM AEDT

With so many cameras and lenses flooding the interchangeable lens market these days, it is easy to become confused when considering compatibility and suitability of equipment. One issue which often trips up beginners is crop factor.

Whether your camera is a Full-Frame Camera, APS-C format camera, or even smaller, will sometimes affect what lenses can be mounted on the camera, and also what field of view a certain lens will provide.

Commonly Asked Questions

  • Is this lens compatible with my current camera?
  • How will the smaller sensor of my camera effect the focal length of the lens?

These are some of the commonly asked questions which we will be attempting to help you answer today.

 

Understanding Crop Factor

Understanding Sensor Size

One of the most important things when understanding crop factor, is that the figures provided are based on the standard sensor size being a full-frame sensor. This is a sensor which is the same width as a piece of 35mm film.

Entry-level DSLRs and Mirrorless cameras generally feature smaller sized sensors, such as the common APS-C sized 15.6 x 23.5mm, or the Canon variant 14.8 x 22.2mm.

 

Understanding Crop Factor

The Canon EOS R and its Full-Frame sensor

What Is Focal Length?

The easiest way to describe focal length is the measurement of the distance between the lens and your camera's image sensor when your subject is in focus. Understanding what this means is less important than understanding what the numbers relate to.

In its most basic form, focal length determines the angle of view of an image, or how much of an image can be captured. A lens with a smaller focal length will have a wider angle of view than a lens with a larger focal length, and will consequently be able to capture more of the scene before you.

How Does Sensor Size Affect Focal Length?

In the pre-digital age, all SLR cameras used the same sized film, which meant when using a lens of the same focal length, all cameras would capture the same field of view (Ignoring Large and Medium Format cameras). With the advent of digital photography, and most modern cameras featuring smaller image sensors, the issue of crop factor was born.

The same lens when mounted on an APS-C camera provided a narrower field of view, compared to if it was mounted on a Full-Frame camera.

Understanding Crop Factor

The Canon EOS 7D Mark II and its APS-C sensor

What Are The Real World Implications?

If you have never used a 35mm film or Full-Frame digital camera, you are likely not bothered by crop factor and the impact it has on the focal length of lenses. If you are coming from a film background, however, or you wish to be on the same page when discussing field of view, it is handy to have a basic understanding.

Working out the equivalent focal length of a lens

There is a formula available for working out the crop factor of your camera based on its sensor size but we will save you the problem and provide some common ones below:

Canon EF-S 1.6x
Canon EF-M 1.6x
Nikon DX 1.5x
Sony E-Mount 1.5x
Pentax DA 1.5x
MFT (Olympus & Panasonic) 2x
Fujifilm XF 1.5x
 

 

Based on the above information, you can work out that mounting a 50mm lens on a Nikon DX camera will provide you with the equivalent focal length of 75mm. (50mm X 1.5 = 75mm).

This setup would provide you with the same field of view as if you mounted a 75mm lens to a full-frame camera.

Choosing your lens accordingly

As a way to combat the effect of crop factor, some camera manufacturers have produced certain lenses which are specifically designed for use on their smaller-format cameras and others which are for full-frame models.

Generally, full-frame compatible lenses will work on smaller-sensor cameras as well, while the lenses designed for smaller sensors will not work of full-frame cameras without issue (Ie. Vignetting, or automatic cropping of the camera's sensor).

In other cases, such as Olympus and Panasonic and their Micro Four Thirds range, lenses have been created with focal lengths that reflect their smaller sensor. An example of this is the Olympus 45mm f1.8mm lens providing a portrait-friendly 90mm equivalent when mounted on compatible cameras.

 

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