Re: [Leica] DIY Rangefinder adjustments

[John Collier <jbcollier@home.com>]

Here is a message from the archives:

> 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.


>> From: "Craig Roberts" <croberts@zoomtel.com>
>> 
>> Back when I owned an M4 it seems I was required to make rangefinder
>> alignment adjustments fairly frequently.  I have since read that the M4 was
>> purposely built that way, the argument being that the proliferation of Leica
>> dealers and repair persons back then made periodic...annual, for
>> instance..."tweaking" feasible.
>> 
>> At any rate, many years ago my local Leica dealer / repairman taught me how
>> to adjust the rangefinder coincidence at infinity...but I don't remember the
>> procedure.  I'd like to do the same with my M3 since it's slightly out of
>> whack (the rangefinder travels past infinity very slightly), but don't wish
>> to make matters worse by "fiddling".   For that matter, I might be
>> overreacting.  The misalignment at infinity may be so small as to make
>> focusing errors imperceptible anyway (I've never had any experience with the
>> incredibly large and precise M3 viewfinder image).
>> 
>> Any advice?
>> 
>> If rangefinder alignment on the older M-series cameras is user-friendly, how
>> is it done?
>>