Crop Factor APS-C vs Full Frame

Crop Factor: APS-C vs Full Frame

Crop factor compares the diagonal of a full-frame sensor (36×24 mm) against the diagonal of a smaller one: crop = diagonal_FF ÷ diagonal_sensor. You'll run into a handful of common numbers. Canon APS-C is 1.6×, while Nikon, Sony and Fuji APS-C sit at 1.5×. Micro Four Thirds is 2.0×, and medium format drops below 1.0×.

To get the equivalent focal length, use f_equiv = f_real × crop. Put a 50 mm lens on a Nikon APS-C body and it frames like a 50 × 1.5 = 75 mm would on full frame. Bigger sensors also give shallower apparent depth of field at the same framing. People sometimes write this as LSE (Light Stops Equivalent), multiplying the aperture by the crop factor so you can line up exposure and bokeh across formats.

Applications

Handy if you're switching systems, mixing cameras on the same video shoot, weighing up prime focal lengths before buying a lens, or working out field of view for astrophotography. The crop factor also matters when you're reading EXIF data or building a rig that mixes full-frame and crop bodies.

FAQ

Why is Canon APS-C 1.6× instead of 1.5×? Canon's APS-C sensor is a touch smaller (~22.3×14.9 mm) than the one Nikon, Sony and Fuji use (~23.6×15.7 mm), and that smaller area pushes the crop ratio up.

Does crop factor change the aperture? The physical f-number stays put, but depth of field and the total light collected both scale with sensor area. If you want to reproduce a full-frame look, multiply focal length and aperture by the crop factor.

What is 35 mm equivalent on Micro Four Thirds? Just multiply by 2.0×. A 17 mm M4/3 lens covers the same field of view as a 34 mm on full frame.