Archived posting to the Leica Users Group, 2001/06/06

[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]

Subject: Re: [Leica] Rangefinder calibration
From: John Collier <jbcollier@powersurfr.com>
Date: Wed, 06 Jun 2001 21:09:52 -0600

Two sequential messages from the archives on rangefinder adjustment:

- ----------
From: Rick Dykstra <rdandcb@cybermac.com.au>
Reply-To: leica-users@mejac.palo-alto.ca.us
Date: Mon, 15 May 2000 10:55:37 +1000
To: leica-users <leica-users@mejac.palo-alto.ca.us>
Subject: [Leica] rangefinder adjustment - long

Hi folks.  On the topic of rangefinder adjustment .....

It's one thing to calibrate the lens to the rangefinder, but it would be
nice to know that the subject is then focussed on the film plane. To
check that, a focussing screen resting on the film guides is needed.
More on this later.

When I look through the lens mount of an upside down M6, I see three
slotted screws. The following describes what I think they're for.

The screw closest to the lens mount supports a roller that rides on the
lens' cam as the lens is focussed. This screw appears to be
eccentrically mounted on the rangefinder arm. Turning this screw would
adjust the relationship between the lens' cam and the rangefinder. This
looks like the screw for fine adjustments to the way the rangefinder
reads the lens' cam.

The second screw in from the lens mount holds the rangefinder arm onto a
swivelling pin that descends from the optical unit.  Between this
screw's head and the rangefinder arm is an eccentric washer, that itself
sits within a recess of the rangefinder arm.  I see two possibilities
here.  If this second screw was partially tightened, then the eccentric
washer, upon being rotated clockwise, would serve to hold the arm in the
right place before the screw is fully tightened.  On the other hand, if
the rangefinder arm has a slotted hole, then the eccentric washer could
be rotated to lengthen or shorten the extension of the rangefinder arm
from its pivoting point.  I think the former of the two possibilities is
the correct one.  This second screw and the eccentric washer look like
they're for rough setup adjustment of the rangefinder, with the
eccentric roller screw (the first screw) being for fine adjustment.

The third screw in from the lens mount is also surrounded by an
eccentric washer. Lying against the washer is a metal arm with a twist
in, held by and pivoting from the second screw.  This arm comes into
contact with the third screw's eccentric washer when the rangefinder arm
moves all the way forward, such as when the lens is removed. Loosening
the screw and turning the washer would adjust the forward most limit of
the rangefinder arm's movement, and might protect other elements within
the rangefinder system from being knocked around when the lens is
removed.  
 
***

So, if an M6 rangefinder does not show correct focus when the lens is
focussed at the film plane, to my way of looking at those screws, its
the first screw, the one with the roller, that should be adjusted.  I'd
leave the other two alone.

A while back someone on list pulled from the archives a description of
how to bend a pair of slotted screwdrivers for this adjustment job.  One
ends up with the screwdriver tip in line with the right angle bend and
the other with its tip square on.  Someone else recently mentioned that
the arm should be supported when the roller screw is being adjusted. The
adjustment itself - trial and error!

In making an adjustment, one could either set the lens to infinity and
adjust the rangefinder to suit, accessing from the back with the lens
attached if feeling confident.  Or, focus the lens on an object up close
by viewing a focussing screen sitting against the film guides and then
take the screen away, stick the screwdriver in from the back and adjust
the rangefinder to suit.  Leica workshops have a jig, a lens and I think
a focussing screen for doing the latter.  With the adjustment done for
up close focussing, intermediate and infinity focussing is then
assessed.  If the rangefinder is out at infinity, then it would appear
to be the lens that's at fault.  Uh oh.


How does all that sound?  I'll stand by while you get to work with your
screwdrivers. On your cameras! Or, send 'em to me and I'll have a go.
So far, mine haven't needed adjusting, but you can see I'm looking
forward to the day that they do!

Rick Dykstra

- ----------
From: John Collier <jbcollier@home.com>
Date: Mon, 15 May 2000 00:17:07 -0600
To: <leica-users@mejac.palo-alto.ca.us>
Subject: Re: [Leica] rangefinder adjustment - long - longer!

The three screws are almost exactly as you described. The third screw with
the eccentric behind the rangefinder's arm limits the "inward" travel of the
rangefinder arm and the thin "flap" off the rangefinder pivot that contacts
this same third adjustment limits the "outward" travel. So we can limit the
rangefinder's movement, not something that we need lose sleep over, and we
can also adjust the roller's vertical position by bending the arm. These
adjustments are factory set and only need readjusting after catastrophic
events such as we have nightmares about. Let us disregard them. The roller
is indeed on a eccentric screw and it does the fine adjustment of the
rangefinder's arm rotational position. The rangefinder arm is attached to
the rangefinder mechanism at the pivot end by yet another eccentric. This
one has a lock screw and the eccentric is adjusted by moving the slotted
tab. This adjusts the range of rotation a given lens cam movement will
impart by changing the length of the arm. A shorter arm gives more rotation
and a longer arm gives less rotation. One checks the rangefinder at
infinity, at 10 meters and at 1 meter. One has to adjust the length of the
arm so that when the roller eccentric adjustment is done to give correct
indication at infinity, the other two are correct as well. It is a Zen
thing. The factory and distributors do not use lenses to do this but a
special jig with a mount for the camera and a target with all the various
marks so you can do the above adjustments and more. The rangefinder arm is
worked with a special tool that mounts on the lens bayonets and has stops
for each of the three measuring points. Cool. The more I learn about this
the more inclined I am to leave it alone ;-). One could easily rig up
targets at fixed distances but one would have to use a ground glass to
compare focus between the rangefinder and the film plane. I hope this has
helped to clear things up somewhat. After a good solid whack, it is not
unusual for the infinity indication to be off. Commonly people then reset
the roller position to correct things. I do not know what actually gets
shifted but it is reasonable to assume that range of rotational movement
does not need to be changed, so we do not have to adjust the length of the
arm, but that the infinity just needs to be reset by adjusting the roller. A
very long winded reply to say: Yes, tweak the roller eccentric for minor in
service adjustments.

John Collier