Re: [Leica] Linearity adjustment on M3

[John Collier <jbcollier@shaw.ca>]

Hi Dante,

I guess the first question would be how the camera works with other 
lenses? I have had lenses that were "off" though it is more common for 
the camera to need tweaking. As you have noted, with old lenses or 
cameras, who knows how many times they have been repaired and by whom?

The rangefinder on the M camera has two main horizontal calibration 
adjustments. One is the position of the roller and the other is the 
length of the arm. You set the position of the roller so that everything 
lines up at infinity and then check at 10m and 1m. The roller position 
adjustment is done with the eccentric screw holding the roller to the 
arm.

The length of the arm governs the amount the shaft up to the rangefinder 
rotates for a given roller movement. A long arm gives less shaft 
rotation than a short arm for a given roller movement. The arm attaches 
to shaft with an eccentric pivot for the adjustment. So if you are 
ending up with the actual point of focus in front of the indicated focus 
then you need to shorten the arm to increase the rate of shaft rotation.

Alas I have no advice on the lens adjustment as I have never (Did I say 
never? Well hardly ever.) have had M lenses apart.

Good luck

John Collier

On Sunday, May 5, 2002, at 05:43 PM, dante@umich.edu wrote:

> The specific problem is that the camera seems to line up at infinity 
> (focus
> and RF) but at close distances focuses behind the subject (as in a few 
> feet
> behind).
>
> The only thing I have been able to surmise is that either
>
> (a) the lens (a 50mm Nikon lens) is not collimated or otherwise is now 
> other
> than 51.6mm FL (I did notice that the front group was screwed in a 
> little
> past where the selected aperture matched -- probably the work of that 
> damn
> Canon ND filter); or
>
> (b) the rate of change in the RF mechanism is somehow wrong.
>
> While I would love to believe the problem is (a) (I unscrewed and 
> reseated
> the front group), it had no apparent effect when I did a crude 
> comparison of
> the film-plane focus and the RF (now when the RF says on at 6 feet, you 
> have
> to turn the lens a little more toward infinity to get the film plane to
> focus).  Also, the problem manifested itself with a Leica 35/2 as well.
> Neither lens presented a problem on my Hexar RF.
>
> ???
>
> I just sent it all out to be fixed today, so I guess I'll find out.
>

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