[Leica] focus at infinity

[Jim Laurel <jplaurel@microsoft.com>]

Speaking of focus at infinity, which do you trust?  The rangefinder or the
lens' infinity stop?  You'll notice that when you set any M lens at the
infinity stop, the coincident images in the rangefinder patch are just ever
so slightly off.  You just barely back the lens off the infinity stop and
the coincident images line up perfectly.  I'm talking about a difference
equivalent to the width  of a hash mark on the lens barrel.  All my
rangefinders do this, including both M6s and the Mamiya 7 and the dealers
for both cameras tell me it's normal and done to allow for
expansion/contraction of materials in varying temps.  Indeed, on hot days,
this effect seems to be less pronounced than on cold days...

I assume the infinity stop is "true" infinity, right?  This probably doesn't
matter since I can never tell the difference between frames taken at the
infinity stop or backed off to make the rangfinder line up, but would like
to hear the group's comments.

- --Jim Laurel