[Leica] More fun w/Noctilux and M3

[Chandos Michael Brown <cmbrow@mail.wm.edu>]

Following my earlier posting about the "looseness" of the Noctilux on my 
M3, I spent a pleasant couple of hours fiddling around with both.  I offer 
a few conclusions based on the purely empirical nature of my research.  To wit:

Both the 50/1 and the 75/1.4 exhibit a similar propensity to uncouple from 
the M3.  Through repeated and accurate testing, I determined that there's 
enough play in the M3 lens flange locking mechanism to allow for lateral 
movement of the lens in the mount (rather than the rotating movement that 
mounts and locks the lens).  Often this movement (< .1mm) is sufficient to 
lift machined notch in the lens flange clear of the locking pin, which in 
turn, allow a minor rotation to loosen the lens in the mount.

For the purposes of experimentation, I adjusted the height of the locking 
pin by shimming it w/ a bit of film-stock (it's tougher to describe this 
than to do it).  This modification dramatically improves the security of 
the lens.

This accomplished, I thought to examine the degree of wear in the mount be 
comparing it with an M4P.  The 50/1 and 75/1.4 mount securely to the M4P 
with *no* play whatsoever.  What I notice immediately is this: the M4P 
mount was re-engineered precisely to correct this problem w/ the M3.  The 
M4P beefs up the lug directly beneath the locking pin, in effect, 
increasing the coupled lug-to-flange surface area of the lens/body mounts, 
which, in turn, prevents lateral movement in the lens.  The M3 relies more 
than the M4P on the spring tension of the mount to secure the lens.  I 
don't use an M6, but I assume that it incorporates the M4P design or some 
refinement of it.

Preliminary conclusion:  while the M3 VF is wonderfully well suited to the 
Noctilux, I'm not entirely certain that the mount is robust enough safely 
to accommodate the lens.  I'm not going to stop using it, but I offer these 
observations as a caution . . .

Chandos


Chandos Michael Brown
Assoc. Prof., History and American Studies
College of William and Mary

http://www.wm.edu/CAS/ASP/faculty/brown