Focal length converter

This page is a summary. For anything more specific, ask: /ask/what-is-50mm-f1-8-on-aps-c-in-full-frame, or any question as words after /ask/.

A focal length is a property of the lens, but how much of the scene it shows depends on the sensor behind it. A 50mm lens frames like a 75mm on full frame when it sits in front of an APS-C sensor, and like a 100mm in front of Micro Four Thirds. To compare lenses across systems, convert them to the same format; full frame is the usual reference.

How it works

Multiply the focal length by the sensor's crop factor to get its full-frame equivalent. To go between two smaller formats, multiply by the first crop factor and divide by the second. Crop factors are measured on the sensor diagonal, so formats with a different shape (4:3 against 3:2) frame slightly differently across the width.

Aperture and depth of field

The f-number sets exposure, and that doesn't change with sensor size: f/2.8 gives the same brightness on a phone as on medium format. Depth of field does change. At the same framing, multiply the f-number by the crop factor to get the full-frame aperture with the same depth of field: f/1.8 on APS-C gives about the background blur of f/2.7 on full frame, and f/1.8 on Micro Four Thirds about that of f/3.6.

Ask it

The converter also answers questions at /ask/: try /ask/what-is-25mm-on-micro-four-thirds-in-full-frame, or name a camera, as in /ask/56mm-on-the-fujifilm-x-t5-full-frame-equivalent. Every camera in the gear catalogue knows its sensor size.

Crop factors