Full-frame equivalent focal length,
made simple
▸ See it in the simulator
Everyone learned focal lengths on full frame — a 50mm "normal," a 24mm "wide," an 85mm "portrait." Put those lenses on a smaller sensor and the framing changes, so we quote a full-frame equivalent: the focal length that would give the same field of view on full frame. It's just a shared yardstick.
That's it. Multiply the lens by the camera's crop factor and you know how it frames in full-frame terms.
| Lens | On Super 35 (1.5×) | On MFT (2.0×) | On Super 16 (3.0×) |
|---|---|---|---|
| 18mm | 27mm | 36mm | 54mm |
| 25mm | 38mm | 50mm | 75mm |
| 35mm | 53mm | 70mm | 105mm |
| 50mm | 75mm | 100mm | 150mm |
Here's where people get burned: equivalence converts field of view, not aperture brightness. An f/2.8 lens exposes at f/2.8 on any sensor — a Micro Four Thirds shooter doesn't lose two stops of light. What does change with a smaller sensor is depth of field: you get more of it at the same equivalent framing. But your exposure meter never cares about crop factor.
Short version: multiply focal by crop for framing. Leave the f-number alone for exposure.
focalcomp shows the effective focal, the full-frame equivalent, and the actual field of view for any camera-and-lens build — and draws it on a fixed scene so you can just see the framing.
Does f/2.8 become f/5.6 on Micro Four Thirds?
No — for exposure it stays f/2.8. The "equivalent aperture" you sometimes see (f/2.8 × crop) only describes depth of field and total light gathered, not the brightness your sensor meters. Set exposure by the real f-number.
Is equivalent focal length the "real" focal length?
No. The lens's real focal length never changes — equivalent is just a translation into full-frame terms so you can picture the framing.
How do I find my camera's crop factor?
It's on every camera page, derived from the real sensor size. Then multiply by your lens.