How do I convert a focal length between two different camera systems?

Multiply your source focal length by its sensor's crop factor, then divide by the target sensor's crop factor. A 50mm lens on APS-C (1.53x computed crop factor) converts to roughly 38.4mm on Micro Four Thirds (1.9994x): 50 × 1.53 ÷ 2.0 ≈ 38.4mm — the real Micro Four Thirds focal length that reproduces the same field of view, routing through full frame's shared 76.7mm-equivalent reference internally even though you never have to write that intermediate number down yourself.

Why Full Frame Is the Reference Point, Not a Detour

Every sensor format's crop factor is defined relative to full frame specifically, so converting between two other formats genuinely does route through that shared reference internally, even if you skip writing out the intermediate full-frame-equivalent number by hand. Trying to derive a direct APS-C-to-Micro-Four-Thirds ratio without going through full frame is mathematically equivalent, but far more error-prone to do by hand, since it's easy to invert a ratio or mix up which crop factor belongs to which format.

The Direction Matters, and It's Easy to Invert by Accident

Converting from a smaller-crop-factor format to a larger one lengthens the equivalent focal length; converting the other direction shortens it. A common mistake is dividing when you should multiply, or vice versa, especially when converting to or from a medium-format sensor whose crop factor sits below 1.0 — always sanity-check that a conversion toward a physically smaller sensor produces a shorter real focal length, and toward a larger sensor produces a longer one.

Skip the manual arithmetic and get the exact figure between any two formats in the Crop-Factor & Equivalence Converter, pre-filled with APS-C to Micro Four Thirds.