Full-Frame Equivalent

Full-frame equivalent is a way of expressing the field of view of a lens on a specific sensor size in terms comparable to the 35mm film standard. For M43, the conversion multiplies the native focal length by the 2x crop factor. A 25mm M43 lens has a 50mm full-frame equivalent, meaning it captures the same angle of view as a 50mm lens on a full-frame camera. This value is used when comparing lenses across camera systems with different sensor sizes.

The full-frame equivalent focal length only describes field of view. The other properties of the lens, including its maximum aperture, the amount of light it transmits, and its optical construction, are determined by the actual focal length. A 25mm f/1.4 M43 lens collects the same amount of light as any other 25mm f/1.4 lens. The sensor size determines how much of the image circle is captured, not how bright the image is. Exposure calculations use the actual aperture, not the equivalent.

Depth-of-field equivalence requires applying the crop factor to the aperture as well as the focal length. A 25mm f/1.4 M43 lens gives a 50mm equivalent field of view, but the depth of field is equivalent to approximately f/2.8 on full-frame at the same framing. This is because achieving the same framing at the same distance on M43 requires a shorter focal length, and shorter focal lengths produce deeper depth of field at the same f-stop. The full-frame equivalent aperture for depth-of-field purposes is obtained by multiplying the actual f-number by the crop factor.

Zoom lenses with a focal length range are also described by their equivalent range. A 12-40mm f/2.8 M43 zoom covers a 24-80mm full-frame equivalent range. The full-frame equivalent is a comparison tool, not a specification of the lens itself. Manufacturer datasheets always list the actual focal length. The equivalent is calculated and included in m43lab lens data to help photographers compare M43 lenses with lenses they may be familiar with from other formats.