Re: [Leica] Rangefinder precision

[TTAbrahams@aol.com]

Mark wrote:
 >So you have lenses dedicated to certain cameras but work ok on other 
cameras?
 >Or only work on certain cameras?
>Can I get my one camera to work perfectly on all my lenese. 
>I missed my focus on a bunch of 135 APO headshots recently and although
>I could have been otherwise delirious I was wondering if my focus
>adjustments were somehow out of wack. I was stopped down to f11 in the 
studio.
>Mark Rabiner


Mark, At f11 you should have had no problem, even with the 135/3,4. I have 
found that some of the really fast lenses need a bit of "tweaking" of the 
camera to perform well wide open. The M3/Nocti combo is a good case in point. 
At 1-1,5 meter at f1, the depth of field is minuscule and I have adjusted the 
rangefinder to give me that dead on. The 75/1,4 tends to have a bias, either 
it is perfect at the 2-4 meter range and slightly off at longer distance, or 
off by a couple of inches in the close range. There is a way to do this, 
either by adjusting the rangefinder close focus setting (that's the easy way) 
or by adding or subtracting material from the focus cam of the lens (the hard 
way). You can check it by sticking the camera on a tripod, remove the back 
door and insert a groundglass on the filmrails of the body. Measure off from 
the filmplane of the camera (I use the slightly dangerous procedure of 
running a tape from the film rail, through the lens mount to a post (white) 
that is placed on the floor. Measure of 1meter exactly (at f1 your depth of 
field is counted in mm at 1meter), put the lens in place, place groundglass 
on rail and check that the lens is focussed at 1meter on the barrel and that 
the post is sharp in the rangefinder patch. If it is sharp, you are home 
free, if not, you have to have the rangefinder close focus cam adjusted (and 
also the rest of the rangefinder corrected, any adjustment on the close focus 
cam will affect the rest of the focus-mechanism). Oh, you should leave the 
shutter on B for this and use a cable release with a VERY secure clamp on the 
release. The sound of a Leica shutter hitting a steel measuring tape is 
rather unnerving to say the least. 
 It is usually not necessary to perform this procedure on the slower lenses 
or with the 35/1,4 and 50/1,4; there is enough leeway in the depth of field 
to compensate. The Noctilux and the 75/1,4 does not allow any slop if they 
are used wide open.
 I have done this procedure several times over the years, but I will only do 
it on my own cameras or my own lenses. One of the more harrowing processes is 
to add material to the focus-cam of the Noctilux. This was done using 
silver-solder and a jeweller's soldering torch and the cam was later filed to 
fit perfectly. The flame of the torch is VERY close to the rear element of 
the Noctilux! (a winecork was inserted to absorb some of the heat and also to 
protect the rear element). I had someone else do it and I have still not 
worked up the nerve to do it to my latest  Noctilux and M6TTL HM. One day I 
will try it though.
All the best and stay focussed,
Tom A