Archived posting to the Leica Users Group, 2002/04/27

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Subject: [Leica] Film register problems for everyone?!
From: "" <>
Date: Sat, 27 Apr 2002 11:47:14 -0400

I was discussing the issue of film-flange register with a certain repair
wizard who lives up on a mountain. The question was how you would check
film-flange register on a given camera/lens combination. The conversation
started with my idea of having my Hexar RF tested against a selection of
lenses and concluded with my wondering if it was my M3 instead that needed
to be checked.

First, besides telling me that as a real world test it is impossible to do
because the film starts to bow inward after a minute (relative humidity
changing); he also shared this interesting insight: Leica late LTM (IIIc and
on) and M bodies contract over time, enough to cause the body focus to
change. This is the same principle which makes boring out old engine blocks
more attractive than using new ones; the cylinders keep their shape. If I
recall, he called it "seasoning" of the alloy.

To be fair, this isn't just Leica, but anything with a diecast chassis (ever
wonder why old SLRs sometimes focus a hair past infinity?). Leitz perceived
this to be such a problem in the screwmount era that it advertised that they
were made of metal stampings to improve precision and stability. Then they
started die-casting and the party line became that die-casting was better
(in reality, die-casting allows smaller tolerances but apparently does
nothing to promote stability).

Second, register problems do not manifest themselves with lenses like the
Summilux 75 close-up, but rather with fast, wide lenses at infinity. Wide
lenses have very little focus travel at the longer distances, and if there
is a register problem (like body focus being too long), the lens will fall
well short of focusing at infinity or focus well past it. This would tend to
suggest that a lot of the people with troublesome Summilux 75s and Leica M6s
close up are having rangefinder or lens problems, not register problems.
Having used a 21/2.8 both on my M3 and my Hexar, both seem to be fine at
f/2.8 at infinity at 50x. My interlocutor said that that fact suggested that
it was unnecessary to test either camera.

My personal conclusion from this is that is that a lot of old M cameras
probably have less than ideal body focus and that the modern Ms (of whatever
brand) are heading that way. It also makes me think twice about all of this
(probably manufactured) argument about the Hexar RF's register distance
being slightly longer, (1) because most people who have complained about
focusing problems have complained about long lenses not focusing
(=rangefinder alignment); (2) because the Leica frame of reference on any
camera before the M6 (1985) is a moving (contracting) target; and (3) given
the nominal dimensions of the Hexar FFR (28.00 +/- 0.03mm) vs. the Leica M
(27.95 +/- 0.01), it seems just as likely that after 10 years, a Hexar RF
could have a FFR closer to Leica spec than a Leica does.

I suspect that the Hexar RF is now mfd to the same FFR as the Leica (27.95
to the inner rails). because it seems that everyone who has had real
register problems has had a low-S/N Hexar. Even then, the majority of
complaints I have seen have centered around focusing long and/or fast normal
lenses.  I surmise that Konica figured out the problem fairly early on.

The solution to all of this seems to be checking body focus (on any camera)
every 10 years or so.

- ------------
Dante Stella

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