Back in the days when my only film camera was a Canonet, I went hog wild and bought every damn 48mm filter on eBay
One of those thousands of filters was a set of Vivitar 1, 2, and 3 closeup filters. They came with a huge chart of "rangefinder distance > closeup distance" conversions, but when I'm out and about (or even at home) with these filters I don't want to be looking up charts and stuff
And since I want to be using these closeup filters for CLOSEUP photos (who woulda thought?), I just memorized one conversion: if the Canonet is at minimum focus distance, I use the No.3 closeup at 10" away. This works really well, as you can see in these photos:
So if they work so well on a Canonet, why not try them on ... every other rangefinder I have?
None of these cameras have filter threads, so I literally just hold them right up against the lens (the XA is the most hilarious because the clamshell gets in the way). Again, minimal focusing distance (on most of my rangefinders it's right around 2.8ft) and 10".
XA
Contax T
Polaroid 100 (getting the field of view right was extremely challenging on this one. also, I measured the 10" from the idol's head, so I guess on this camera I should hold it more like 11-12" away)
BTW, it also works well on my Pentax SLR with an adapter ring:
