Yeah, If I were (as an semi-experienced amatuer photographer) to describe focusing with a rangefinder; I would say:
- It is simple in theory
- It is intuitive and obvious
- It helps to have good eyesight
- above all else, it really rewards PRACTICE
When you look through a leica veiwfinder, you see the whole scene before you - and superimposed over it are the bright framelines to help you compose (these are a guide only), and in the middle - the rangefinder patch.
I only have one M lens, a C-Sonnar 50mm f1.5, so this is my point of reference. It has a total focus throw of about 90° from 0.9m-infinity.
At f2.8 focusing on a subject at aboout 2m away, you have about 20cm depth of field. Already getting a sharp subject requires the focusing ring be aligned within a fraction of a degree.
At f1.5 (but otherwise as above) you have 10cm DoF - and the point of sharpest focus shifts towards you by about 15cm
which the rangefinder patch cannot adjust for so you have to "wing it".
I think Bernd said in another thread that rangefinders "Can be a nervous horse to ride on" - I wholehearedly agree.
Hovever,
and this is really important... It's FUN!
The satisfaction of learing how to use a lens, and eke the best out of it in different situations, might not be for everyone - but I think it is for me!
Using a rangefinder is a great teacher, if you can put up with the lessons. And not being at the mercy of autofocus is wonderful, I can completely see how after a few years regular use you would never go back.