It's been noted already that the different 25mm lenses in the system have slightly different fields of view, with the Olympus 25mm/1.8 having a wider field of view than the others. The question is, what is the "true" focal length that all the 25mm lenses have? I noticed that in theory we already have all the information that we need to calculate the "true" focal length, at least at one focus distance, and that's the minimum focus distance, thanks to our handy Optics 101 formula: Focal Length = Working Distance / (1 + (1 / Magnification)) Here's where it gets weird, though. Using the published data, the results are a little bit out there: Olympus 25mm/1.8 MFD: 238.8mm Magnification: 0.12x FL: 25.6mm Panasonic 25mm/1.7 MFD: 250mm Magnification: 0.14x FL: 30.7mm Panasonic 25mm/1.4 MFD: 300mm Magnification: 0.11x FL: 29.7mm Voigtlander 25mm/0.95 MFD: 170mm Magnification: 0.26 FL: 34.7mm (!) I imagine that there must be some form of focus breathing happening with the Voigtlander especially due to some floating elements or something, but the results are kind of puzzling to me. Especially since they all claim the exact same 47 degree FoV (which is clearly not true). As a bonus, I checked the Sigma and Panasonic 30mm lenses, since the "true" FLs seemed to be clustered around there. Sigma 30mm/2.8 MFD: 300mm Magnification: 0.125x FL: 33.3mm Panasonic 30mm Macro MFD: 105mm Magnification: 1 FL: 52.5mm So obviously the macro is doing special stuff internally to get to 1:1 (which also explains why the lens is 64mm long perhaps?), but it's curious to see the Sigma 30mm so close to the calculated FLs of the Panasonics and the Voigtlander. Anyone got a Sigma 30mm and one of the other lenses to test out the hypothesis a bit more?