The Fujifilm X-Pro 1's optical viewfinder mode automatically switches magnification to match the prime lens mounted. There's a "bright frame" electronically drawn as a heads-up display showing the area of the actual frame.
I have the 35mm lens mounted. When I picked up the camera a little bit ago, I discovered that the view through the finder was wider than it has been in my previous few days of using the camera, and that the bright line rectangle was smaller than I was used to. It seems to have switched to a wider view.
After puzzling at the controls and the manual for a while, I couldn't figure it out. I eventually unmounted and remounted the lens, after which everything was back to normal. But the camera seemed to always "know" the right focal length, as it drew the bright frame appropriately.
How did the camera get into this state? A glitch, or something I inadvertently changed? Is it possible to do on purpose? (I can see an advantage in some situations in having less magnification, in order to see more of the surrounding situation.)
I've searched the manual, but found nothing about this. (Unfortunately, the manual is both poorly organized and full of gaps on many points.)