FFE is short for ‘full-frame equivalent’. What does that mean?

As you know, a lens’ focal length (millimetres) does not tell you whether it’s a wide or a tele lens unless you know what system it’s to be used on. On large format a 50 mm lens is extremely wide, on medium format (6×6), it’s a wide lens, on full frame it’s a normal lens, on APS-C, it’s a short tele lens, on (micro) four thirds it’s a proper tele lens, and so on.

Oddly, no… bizarrely, we’re not describing a lens’ field of view by naming its field of view (you might have known that a 50 mm lens on full frame gives you a 45 ° field-of-view, but can you name the field-of view of any other typical focal length?), but are instead talking about millimetres as if they would really tell us anything.

JAPB is all about mixing and matching — using a lens from one system on another system. While most lens hackers keep within one sensor/film size (e.g. APS-C, Full frame, Medium format), the use of lenses from non-conforming film/sensor sizes offers some tantalizing opportunities. Therefore also, we need to have some way of bridging the difference between the fields-of-view afforded by one lens when used on a totally different system.

While imperfect, we’re using the concept of ‘Full-frame-equivalent’, meaning: If this was a lens designed for full frame, and it gave the same field-of-view, what would its focal length (in millimetres) be? Let’s illustrate this by a coupole of examples:

  1. “The full-frame equivalent of an 18 mm APS-C lens is a 28 mm lens”, which means that an 18 millimetre lens on an APS-C body gives roughly the same field-of-view (or viewing angle) as a 28 mm lens would give on a full-frame (36×24 mm) body.
  2. “The full-frame equivalent of an 80 mm medium format lens is a 50 mm lens”, which means that an 80 mm lens on a medium format camera gives roughly the same field-of-view as does a 50 mm lens on a full-frame camera.
  3. “Olympus’ 12-40 mm f/2.8 lens has a full-frame equivalence of 24-80 millimetres”, meaning that the field of view the Olympus 12-40 lens offers the user of a micro four thirds camera body is (roughly) the same as you would get using a 24-80 mm lens on a full-frame camera.

Importantly, full-frame equivalence applies only to field of view. Therefore, while a 17 mm f/1.2 lens designed for micro four thirds gives you the field-of-view of (roughly) 35 mm (FFE), and actually gathers as much light as its f/1.2 designation indicates, it does not give you the depth-of field a 35 mm f/1.2 full-frame lens would.

« Back to Glossary Index