Put a Helios 44-2 on a Fuji body and it stops being a 58mm lens, at least as far as framing goes. It frames like an 87mm. On an Olympus Micro Four Thirds body it frames like a 116mm. Same glass, same aperture ring, very different lens in practice. Most of the confusion around adapted glass comes from mixing up three separate things: what the sensor crops, what the adapter has to do mechanically, and what a focal reducer changes.