Alan, Matt Alofs went the
DIY eyepiece route.
Have both the Hexar and the R4a, and use 25 and 35mm lenses on both. The full Hexar finder gives a good approximation of 25mm (both cameras have reasonably accurate framelines, i.e., they're not optimistically squeezed in into too high a finder magnification). My 35mm is the f/1.2 version, so I much prefer the Hexar for this, but the R4a will give good results all the time if not focusing particularly close.
The Hexar is better made, but I don't feel there's anything lacking in the Bessa: wind-on isn't as smooth as my old M4, but who cares? Well, probably me, otherwise I'd have sold it by now...
😱
Of the three cameras,
M4: best feel, most accurate focusing, draws most comments from other photographers, most respect from people who know it doesn't have a meter, most incredulity from people who think it's digital
R4a: best for wides, focusing accuracy a grey area for faster and longer lenses, but a stunning achievement for the focal lengths in which RF equipment excels
Hexar: best allrounder, and can shoot ISO 100 in full sun at f/2.8 (sunny 16) without a filter
The Hexar would be the one I'd keep, partly for its top shutter speed and meter, and partly because it's the best fit for the lenses I've chosen. Now if someone would remake it with 21mm framelines and an engraved script on the top plate, they'd have a winner...