Standard Crop Factor How the Camera Model Affects Your Lenses Toms Guide

“Canon’s DSLRs come in a huge range of prices, from the $400 EOS Rebel T5 to the $6,000 EOS-1D X Mark II. One of the factors that determines price is the size of the sensor. Canon’s top cameras use a sensor about the size of a 35mm film frame in old cameras. However, most of Canon’s DSLRs use a smaller sensor, with the jargony name Canon APS-C. (It’s 38 percent the size of a full-frame sensor, but still huge compared to what your cellphone has.)
Credit: Junko Kimura/GettyThe camera’s sensor size determines how images look. For any given lens, cameras with larger sensors capture wider-angle images; those with smaller sensors capture more zoom. Here’s how that works and what it means for the lenses you buy.
How sensor size determines zoom
In Canon cameras with a full-frame sensor, the lens projects the full width of what it captures onto the sensor. But it can project only the center portion of what it captures onto a smaller APS-C sensor. It’s as if you took the full-frame image and cropped off the edges, thereby zooming in to the narrower portion in the center of the image.
The zoom you get when using a smaller sensor is called the crop factor, calculated as the diagonal measure of the full-frame sensor divided by the diagonal of the APS-C sensor. For Canon cameras, this comes out to 1.60. So, switching a lens from a full-frame to an APS-C Canon camera is like zooming in 60 percent more.

The red frame indicates the crop factor from Full frame to ASP-C sensor. Credit: Canon”

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