Hi Peter,
The RF base is shorter on the Barnack-like early Canon RF's. That reduces the accuracy, but has no practical effect when used with the lenses for which they were designed. The cameras were made slightly larger, because of design changes to the shutter crates, the hinged back, etc. That allowed a longer effective baselength for the RF, which was of importance principally with the very fast lenses. The 7series has the longest RF base, and focuses the 0.95 nicely. Wide open that lens has a DOF measured in mm.... Not much room for error.
The II-III-IV series takes a bit of getting used to, because of the bottom loading. They are very small, and very nicely made. The V-VI series, and the P are a bit larger, have a hinged back, and some individual design quirks, like the trigger wind on the VI-T, versus the lever wind on the VI-L.
The articles on the Cameraquest site give a great deal of background on these cameras, and are very helpful.
Any of the bodies, in good shape, will give a good account of itself. They are fine picture-takers. The older ones may need a CLA, and some of the newer ones, as well. There are several techs who can work magic, for a fee.
The P is popular (strange.. that's what the P stood for), has a classically beautiful design, and may be a bit pricey. The 7series is not as highly regarded, but are versatile examples of the last of Canon's design efforts in the RF family. Properly functioning, they are fine cameras.
Read a lot, check over the forum articles by Peter Dechert here on RFF, go to the Canon Museum, and read, read, read. You'll learn a lot, and the good news is that the cameras are relatively cheap now, and easy to find, as well. With the switch to digital, our film stuff is not well regarded in the outside world. Better for buyers that way...
These cameras will do anything the contemporary Leica bodies could do, for a lot less money. That is even more true of the lenses...
Harry
