Originally posted by clackers Well, the 31 and 77 were designed as 35mm lenses, while the 55 works on FF - see other threads, including photos.
For FoV comparisons to other lenses you might have, divide by 1.5. ☺
Of course, the situation will be more complex than just "this lens on FF looks like that lens on APS-C". Depending on your subject, you'll be either standing at the same point and wondering at the extra real estate on a landscape shot or standing at a different point to frame your subject similarly and wondering at how different the background looks.
The latter, I imagine, is part of the reason some people look a little askance at the aperture equivalence argument in debates about the differences between the two formats.