The IIIf mated with some Voigtlander Color-Skopars has certainly has become my travel kit. Even though the M is small, it's not that small
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You will often hear the argument that the M has a larger baseline for more accurate focus especially for longer focal lengths and that that lack of framing for anything other than a 50mm is a real drawback.
Obviously, everyone works differently but for me at least ...
- I shoot 90% of monochrome with either a 21mm or 35mm focal length. Both of these can be well zone focused so as to make the focusing question moot.
- Even my in-camera framing on the M bodies is only really approximate. Up very close, it might matter, but for most things, an aux finder is more than good enough. If I really want precision framing, I use an SLR.
The thing I have found is that zone a focused camera with an aux finder gets the equipment out of the way and encourages me to engage spontaneously with the subject. So much so, I use that 21mm Color Skopar on my M bodies with an adapter ring and ... aux finder
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As always, YMMV...