Crop factor is one aspect of digital cameras that can confuse beginner photographers. Because so many cameras and lenses are flooding the interchangeable lens market these days, the compatibility and suitability of your photography equipment are critical considerations.
Whether your camera uses a Full-Frame sensor, an APS-C sensor, or something even smaller will sometimes affect which lenses can be mounted on it and what field of view a particular lens will provide.
In this guide:
- Commonly asked questions about crop factor
- Understanding sensor size
- What is focal length?
- How does sensor size affect focal length?
- Real world implications
- Working out the equivalent focal length
- Choosing your lens
Commonly Asked Questions About Crop Factor
Crop factors can significantly impact which lenses work with which cameras. The most commonly asked questions about crop factors are:
- Is this lens compatible with my current camera?
- How will my camera's smaller sensor affect the lens's focal length?
To help you understand digital camera crop factor, we first need to explain camera sensors and the sizes available. For a thorough primer on the different sensor size formats available — from full-frame to APS-C to Micro Four Thirds — it's worth reading that guide alongside this one.
Understanding Sensor Size
One of the essential things to understand about crop factors is that the figures provided are based on the standard size of a full-frame sensor, which matches the width of a piece of 35mm film — measuring 36mm x 24mm.
In addition to 35mm film, medium and large format film stocks offer finer grain, better tonal range, deeper exposure latitude, and greater control over focus and depth of field.
As digital cameras entered the market in the late 20th century, entry-level DSLRs and mirrorless cameras featured smaller sensors, such as the standard APS-C size (15.6 x 23.5mm) or the Canon APS-C variant (14.8 x 22.2mm).
The Canon EOS R and its Full-Frame sensor
The difference in size between sensor formats can significantly impact the portion of a scene captured and the overall image quality. Crop sensors capture a smaller portion of the scene than full-frame sensors — which brings us to focal length, another key consideration for lens compatibility.
What Is Focal Length?
Focal length is the distance between your lens and the camera's image sensor when your subject is in focus. It determines the an