Crop Factor Explained: Full Frame vs APS-C vs Micro Four Thirds

Crop factor tells you how much smaller a sensor is than full frame (the 36x24 mm reference from 35 mm film). APS-C is about 1.5x, or 1.6x on Canon; Micro Four Thirds is 2x; a 1-inch sensor is about 2.7x. The multiplier lets you compare lenses and cameras of different formats on one common scale.

Equivalent focal length

Multiply the focal length by the crop factor to get the full-frame-equivalent field of view. A 35 mm lens frames like a 53 mm lens on APS-C, or like a 70 mm lens on Micro Four Thirds. This is why a crop sensor gives extra reach for wildlife: the subject fills more of the frame, even though the lens itself has not changed.

Equivalent aperture - and what it is not

Multiply the f-number by the crop factor to compare depth of field and total light gathered: f/2.8 on Micro Four Thirds behaves like f/5.6 on full frame for background blur. Crucially, this does not change exposure. A 50 mm f/1.8 still meters and exposes at f/1.8 on every format; only depth of field and gathered light scale with the crop factor.

Which format to choose

Bigger sensors gather more light and blur backgrounds more easily; smaller sensors are lighter, cheaper and give more reach and depth of field. None is simply better - it is a trade-off you match to the photography you do.