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CROP FACTOR

ARTICLES > LENSES


Sometimes when an attempt is made to simplify or explain a term or reference point, it can end up complicating the situation. This is exactly what happened – as far as we’re concerned – when Canon introduced the EF-S lens mount. Terms like ‘crop factor’, 'extra reach’ and ‘equivalent focal length’ just aren’t helpful. Here’s why.

BY ROBERT SCOTT, updated 24 May 2022


The EF lens mount was introduced in the same year that the EOS was announced – 1987. EF lenses, like the FD lens system that went before, gave full coverage to 35mm EOS film cameras, then subsequently full-frame – 36 x 24mm sensor – digital cameras.

Then, in 2000, along came a camera with an APS-C 'crop' sensor – the EOS D30. The main reason for the introduction of the smaller sensor was cost – full frame sensors are expensive. Crop refers to the fact that the image you get with the smaller sensor is a cropped part of the image obtained with the full frame sensor.

So what does this all mean for your photography?

Myth-busting

There is a lot of confusion about crop factors, extended reach and telephoto effects when using lenses on APS-C cameras.

First, let’s dispel the myth that the focal length of a lens changes when switched between a full-frame camera and an APS-C camera. It doesn’t.

FACT: Focal length is a characteristic of the lens and is not affected by the camera or sensor size.

Use the same lens on a full frame camera and an APS-C camera, and you end up with results like those below.