VF magnification doesn't impact focusing accuracy. Focusing accuracy is dictated by the distance between the beam splitters -which is the same for all M series.
VF magnification doesn't help you focusing. The RF patch is same size and aligning the split image is again independent of magnification.
But finally we all know the M4 was the best.
No, also the magnification of the image is important here, see the difference of the rangefinders on the Leicas II and III with screw mount.
Erik.
It's not just a matter of focusing ease but system accuracy. Erik is right. The screw mount Leicas have a pathetic physical baselength. The only reason they work so well is because the optical magnification is massive.
You are partly right in that the physical baselength is still important Mark. Theoretically, given the choice, a long physical baselength is the superior way to manufacture a highly accurate rangefinder. Why? Because any mechanical means of driving a beam deflector will have manufacturing tolerances. If you take two different systems, one with a moderate degree of magnification but a long physical baselength; the other, vice-versa, the second will have to made to tighter manufacturing tolerances than the first to achieve the same accuracy. Why? Because by using optical magnification to achieve a large effective baselength—it will unavoidably be magnifying any errors induced by production tolerances of the deflector drive system. A point rarely considered.
The screw mount Leicas get away with it because Leitz obviously achieved a level of manufacturing precision sufficient to preserve the accuracy of their rangefinder installations, despite the substantial magnification used and credit to them for that.
But there is more to rangefinder accuracy than even the right degree of manufacturing precision and a large physical baselength. The ratio of gearing of the system greatly impacts accuracy also. Ie the lower geared the beam deflector drive system is, the more accurate it will be.
So...to produce a rangefinder of not just good, or even excellent, but, superlative precision, you need: a huge effective baselength relying more on physical size, than magnification; excellent precision in manufacture equalling, say Leitz, and; a beam deflector that must rotate through the widest possible arc (Ie gearing). Fortunately one manufacturer produced just such a design and it featured a beam deflector which had to travel
four times as far as the screw mount Leica equivalent, which, together with its massive EBL, produced a system of such accuracy it has never been equalled, let alone surpassed.
